[PATCH v2 00/47] use refcount+RCU method to implement lockless slab shrink

[PATCH v2 00/47] use refcount+RCU method to implement lockless slab shrink

[Qi Zheng]

Hi all,

1. Background
=============

We used to implement the lockless slab shrink with SRCU [1], but then kernel
test robot reported -88.8% regression in stress-ng.ramfs.ops_per_sec test
case [2], so we reverted it [3].

This patch series aims to re-implement the lockless slab shrink using the
refcount+RCU method proposed by Dave Chinner [4].

[1]. https://lore.kernel.org/lkml/20230313112819.38938-1-zhengqi.arch@bytedance.com/
[2]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/
[3]. https://lore.kernel.org/all/20230609081518.3039120-1-qi.zheng@linux.dev/
[4]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/

2. Implementation
=================

Currently, the shrinker instances can be divided into the following three types:

a) global shrinker instance statically defined in the kernel, such as
   workingset_shadow_shrinker.

b) global shrinker instance statically defined in the kernel modules, such as
   mmu_shrinker in x86.

c) shrinker instance embedded in other structures.

For case a, the memory of shrinker instance is never freed. For case b, the
memory of shrinker instance will be freed after synchronize_rcu() when the
module is unloaded. For case c, the memory of shrinker instance will be freed
along with the structure it is embedded in.

In preparation for implementing lockless slab shrink, we need to dynamically
allocate those shrinker instances in case c, then the memory can be dynamically
freed alone by calling kfree_rcu().

This patchset adds the following new APIs for dynamically allocating shrinker,
and add a private_data field to struct shrinker to record and get the original
embedded structure.

1. shrinker_alloc()
2. shrinker_free_non_registered()
3. shrinker_register()
4. shrinker_unregister()

In order to simplify shrinker-related APIs and make shrinker more independent of
other kernel mechanisms, this patchset uses the above APIs to convert all
shrinkers (including case a and b) to dynamically allocated, and then remove all
existing APIs. This will also have another advantage mentioned by Dave Chinner:

```
The other advantage of this is that it will break all the existing out of tree
code and third party modules using the old API and will no longer work with a
kernel using lockless slab shrinkers. They need to break (both at the source and
binary levels) to stop bad things from happening due to using uncoverted
shrinkers in the new setup.
```

Then we free the shrinker by calling kfree_rcu(), and use rcu_read_{lock,unlock}()
to ensure that the shrinker instance is valid. And the shrinker::refcount
mechanism ensures that the shrinker instance will not be run again after
unregistration. So the structure that records the pointer of shrinker instance
can be safely freed without waiting for the RCU read-side critical section.

In this way, while we implement the lockless slab shrink, we don't need to be
blocked in unregister_shrinker() to wait RCU read-side critical section.

PATCH 1: move shrinker-related code into a separate file
PATCH 2: remove redundant shrinker_rwsem in debugfs operations
PATCH 3: add infrastructure for dynamically allocating shrinker
PATCH 4 ~ 21: dynamically allocate the shrinker instances in case a and b
PATCH 22 ~ 40: dynamically allocate the shrinker instances in case c
PATCH 41: remove old APIs
PATCH 42: introduce pool_shrink_rwsem to implement private synchronize_shrinkers()
PATCH 43: add a secondary array for shrinker_info::{map, nr_deferred}
PATCH 44 ~ 45: implement the lockless slab shrink
PATCH 46 ~ 47: convert shrinker_rwsem to mutex

3. Testing
==========

3.1 slab shrink stress test
---------------------------

We can reproduce the down_read_trylock() hotspot through the following script:

```

DIR="/root/shrinker/memcg/mnt"

do_create()
{
    mkdir -p /sys/fs/cgroup/memory/test
    echo 4G > /sys/fs/cgroup/memory/test/memory.limit_in_bytes
    for i in `seq 0 $1`;
    do
        mkdir -p /sys/fs/cgroup/memory/test/$i;
        echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
        mkdir -p $DIR/$i;
    done
}

do_mount()
{
    for i in `seq $1 $2`;
    do
        mount -t tmpfs $i $DIR/$i;
    done
}

do_touch()
{
    for i in `seq $1 $2`;
    do
        echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
        dd if=/dev/zero of=$DIR/$i/file$i bs=1M count=1 &
    done
}

case "$1" in
  touch)
    do_touch $2 $3
    ;;
  test)
    do_create 4000
    do_mount 0 4000
    do_touch 0 3000
    ;;
  *)
    exit 1
    ;;
esac
```

Save the above script, then run test and touch commands. Then we can use the
following perf command to view hotspots:

perf top -U -F 999

1) Before applying this patchset:

  40.44%  [kernel]            [k] down_read_trylock
  17.59%  [kernel]            [k] up_read
  13.64%  [kernel]            [k] pv_native_safe_halt
  11.90%  [kernel]            [k] shrink_slab
   8.21%  [kernel]            [k] idr_find
   2.71%  [kernel]            [k] _find_next_bit
   1.36%  [kernel]            [k] shrink_node
   0.81%  [kernel]            [k] shrink_lruvec
   0.80%  [kernel]            [k] __radix_tree_lookup
   0.50%  [kernel]            [k] do_shrink_slab
   0.21%  [kernel]            [k] list_lru_count_one
   0.16%  [kernel]            [k] mem_cgroup_iter

2) After applying this patchset:

  60.17%  [kernel]           [k] shrink_slab
  20.42%  [kernel]           [k] pv_native_safe_halt
   3.03%  [kernel]           [k] do_shrink_slab
   2.73%  [kernel]           [k] shrink_node
   2.27%  [kernel]           [k] shrink_lruvec
   2.00%  [kernel]           [k] __rcu_read_unlock
   1.92%  [kernel]           [k] mem_cgroup_iter
   0.98%  [kernel]           [k] __rcu_read_lock
   0.91%  [kernel]           [k] osq_lock
   0.63%  [kernel]           [k] mem_cgroup_calculate_protection
   0.55%  [kernel]           [k] shrinker_put
   0.46%  [kernel]           [k] list_lru_count_one

We can see that the first perf hotspot becomes shrink_slab, which is what we
expect.

3.2 registeration and unregisteration stress test
-------------------------------------------------

Run the command below to test:

stress-ng --timeout 60 --times --verify --metrics-brief --ramfs 9 &

1) Before applying this patchset:

setting to a 60 second run per stressor
dispatching hogs: 9 ramfs
stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
                          (secs)    (secs)    (secs)   (real time) (usr+sys time)
ramfs            735238     60.00     12.37    363.70     12253.05        1955.08
for a 60.01s run time:
   1440.27s available CPU time
     12.36s user time   (  0.86%)
    363.70s system time ( 25.25%)
    376.06s total time  ( 26.11%)
load average: 10.79 4.47 1.69
passed: 9: ramfs (9)
failed: 0
skipped: 0
successful run completed in 60.01s (1 min, 0.01 secs)

2) After applying this patchset:

setting to a 60 second run per stressor
dispatching hogs: 9 ramfs
stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
                          (secs)    (secs)    (secs)   (real time) (usr+sys time)
ramfs            746677     60.00     12.22    367.75     12443.70        1965.13
for a 60.01s run time:
   1440.26s available CPU time
     12.21s user time   (  0.85%)
    367.75s system time ( 25.53%)
    379.96s total time  ( 26.38%)
load average: 8.37 2.48 0.86
passed: 9: ramfs (9)
failed: 0
skipped: 0
successful run completed in 60.01s (1 min, 0.01 secs)

We can see that the ops/s has hardly changed.

This series is based on next-20230711, and the [PATCH v2 05/49] depends on the
patch: https://lore.kernel.org/lkml/20230625154937.64316-1-qi.zheng@linux.dev/.

Comments and suggestions are welcome.

Thanks,
Qi

Changelog in v1 -> v2:
 - implement the new APIs and convert all shrinkers to use it.
   (suggested by Dave Chinner)
 - fix UAF in PATCH [05/29] (pointed by Steven Price)
 - add a secondary array for shrinker_info::{map, nr_deferred}
 - re-implement the lockless slab shrink
   (Since unifying the processing of global and memcg slab shrink needs to
    modify the startup sequence (As I mentioned in https://lore.kernel.org/lkml/38b14080-4ce5-d300-8a0a-c630bca6806b@bytedance.com/),
    I finally choose to process them separately.)
 - collect Acked-bys

Qi Zheng (47):
  mm: vmscan: move shrinker-related code into a separate file
  mm: shrinker: remove redundant shrinker_rwsem in debugfs operations
  mm: shrinker: add infrastructure for dynamically allocating shrinker
  kvm: mmu: dynamically allocate the x86-mmu shrinker
  binder: dynamically allocate the android-binder shrinker
  drm/ttm: dynamically allocate the drm-ttm_pool shrinker
  xenbus/backend: dynamically allocate the xen-backend shrinker
  erofs: dynamically allocate the erofs-shrinker
  f2fs: dynamically allocate the f2fs-shrinker
  gfs2: dynamically allocate the gfs2-glock shrinker
  gfs2: dynamically allocate the gfs2-qd shrinker
  NFSv4.2: dynamically allocate the nfs-xattr shrinkers
  nfs: dynamically allocate the nfs-acl shrinker
  nfsd: dynamically allocate the nfsd-filecache shrinker
  quota: dynamically allocate the dquota-cache shrinker
  ubifs: dynamically allocate the ubifs-slab shrinker
  rcu: dynamically allocate the rcu-lazy shrinker
  rcu: dynamically allocate the rcu-kfree shrinker
  mm: thp: dynamically allocate the thp-related shrinkers
  sunrpc: dynamically allocate the sunrpc_cred shrinker
  mm: workingset: dynamically allocate the mm-shadow shrinker
  drm/i915: dynamically allocate the i915_gem_mm shrinker
  drm/msm: dynamically allocate the drm-msm_gem shrinker
  drm/panfrost: dynamically allocate the drm-panfrost shrinker
  dm: dynamically allocate the dm-bufio shrinker
  dm zoned: dynamically allocate the dm-zoned-meta shrinker
  md/raid5: dynamically allocate the md-raid5 shrinker
  bcache: dynamically allocate the md-bcache shrinker
  vmw_balloon: dynamically allocate the vmw-balloon shrinker
  virtio_balloon: dynamically allocate the virtio-balloon shrinker
  mbcache: dynamically allocate the mbcache shrinker
  ext4: dynamically allocate the ext4-es shrinker
  jbd2,ext4: dynamically allocate the jbd2-journal shrinker
  nfsd: dynamically allocate the nfsd-client shrinker
  nfsd: dynamically allocate the nfsd-reply shrinker
  xfs: dynamically allocate the xfs-buf shrinker
  xfs: dynamically allocate the xfs-inodegc shrinker
  xfs: dynamically allocate the xfs-qm shrinker
  zsmalloc: dynamically allocate the mm-zspool shrinker
  fs: super: dynamically allocate the s_shrink
  mm: shrinker: remove old APIs
  drm/ttm: introduce pool_shrink_rwsem
  mm: shrinker: add a secondary array for shrinker_info::{map,
    nr_deferred}
  mm: shrinker: make global slab shrink lockless
  mm: shrinker: make memcg slab shrink lockless
  mm: shrinker: hold write lock to reparent shrinker nr_deferred
  mm: shrinker: convert shrinker_rwsem to mutex

 arch/x86/kvm/mmu/mmu.c                        |  18 +-
 drivers/android/binder_alloc.c                |  31 +-
 drivers/gpu/drm/i915/gem/i915_gem_shrinker.c  |  30 +-
 drivers/gpu/drm/i915/i915_drv.h               |   2 +-
 drivers/gpu/drm/msm/msm_drv.c                 |   4 +-
 drivers/gpu/drm/msm/msm_drv.h                 |   4 +-
 drivers/gpu/drm/msm/msm_gem_shrinker.c        |  36 +-
 drivers/gpu/drm/panfrost/panfrost_device.h    |   2 +-
 drivers/gpu/drm/panfrost/panfrost_drv.c       |   6 +-
 drivers/gpu/drm/panfrost/panfrost_gem.h       |   2 +-
 .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |  32 +-
 drivers/gpu/drm/ttm/ttm_pool.c                |  38 +-
 drivers/md/bcache/bcache.h                    |   2 +-
 drivers/md/bcache/btree.c                     |  27 +-
 drivers/md/bcache/sysfs.c                     |   3 +-
 drivers/md/dm-bufio.c                         |  26 +-
 drivers/md/dm-cache-metadata.c                |   2 +-
 drivers/md/dm-zoned-metadata.c                |  28 +-
 drivers/md/raid5.c                            |  25 +-
 drivers/md/raid5.h                            |   2 +-
 drivers/misc/vmw_balloon.c                    |  38 +-
 drivers/virtio/virtio_balloon.c               |  25 +-
 drivers/xen/xenbus/xenbus_probe_backend.c     |  17 +-
 fs/btrfs/super.c                              |   2 +-
 fs/erofs/utils.c                              |  20 +-
 fs/ext4/ext4.h                                |   2 +-
 fs/ext4/extents_status.c                      |  22 +-
 fs/f2fs/super.c                               |  32 +-
 fs/gfs2/glock.c                               |  20 +-
 fs/gfs2/main.c                                |   6 +-
 fs/gfs2/quota.c                               |  26 +-
 fs/gfs2/quota.h                               |   3 +-
 fs/jbd2/journal.c                             |  27 +-
 fs/kernfs/mount.c                             |   2 +-
 fs/mbcache.c                                  |  23 +-
 fs/nfs/nfs42xattr.c                           |  87 +-
 fs/nfs/super.c                                |  20 +-
 fs/nfsd/filecache.c                           |  22 +-
 fs/nfsd/netns.h                               |   4 +-
 fs/nfsd/nfs4state.c                           |  20 +-
 fs/nfsd/nfscache.c                            |  31 +-
 fs/proc/root.c                                |   2 +-
 fs/quota/dquot.c                              |  17 +-
 fs/super.c                                    |  39 +-
 fs/ubifs/super.c                              |  22 +-
 fs/xfs/xfs_buf.c                              |  25 +-
 fs/xfs/xfs_buf.h                              |   2 +-
 fs/xfs/xfs_icache.c                           |  26 +-
 fs/xfs/xfs_mount.c                            |   4 +-
 fs/xfs/xfs_mount.h                            |   2 +-
 fs/xfs/xfs_qm.c                               |  26 +-
 fs/xfs/xfs_qm.h                               |   2 +-
 include/linux/fs.h                            |   2 +-
 include/linux/jbd2.h                          |   2 +-
 include/linux/memcontrol.h                    |  12 +-
 include/linux/shrinker.h                      |  54 +-
 kernel/rcu/tree.c                             |  21 +-
 kernel/rcu/tree_nocb.h                        |  19 +-
 mm/Makefile                                   |   4 +-
 mm/huge_memory.c                              |  69 +-
 mm/shrinker.c                                 | 772 ++++++++++++++++++
 mm/shrinker_debug.c                           |  76 +-
 mm/vmscan.c                                   | 701 ----------------
 mm/workingset.c                               |  26 +-
 mm/zsmalloc.c                                 |  28 +-
 net/sunrpc/auth.c                             |  19 +-
 66 files changed, 1516 insertions(+), 1225 deletions(-)
 create mode 100644 mm/shrinker.c

-- 
2.30.2

[PATCH v2 01/47] mm: vmscan: move shrinker-related code into a separate file

[Qi Zheng]

The mm/vmscan.c file is too large, so separate the shrinker-related
code from it into a separate file. No functional changes.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 include/linux/shrinker.h |   3 +
 mm/Makefile              |   4 +-
 mm/shrinker.c            | 707 +++++++++++++++++++++++++++++++++++++++
 mm/vmscan.c              | 701 --------------------------------------
 4 files changed, 712 insertions(+), 703 deletions(-)
 create mode 100644 mm/shrinker.c

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 224293b2dd06..961cb84e51f5 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -96,6 +96,9 @@ struct shrinker {
  */
 #define SHRINKER_NONSLAB	(1 << 3)
 
+unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
+			  int priority);
+
 extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
 					    const char *fmt, ...);
 extern void register_shrinker_prepared(struct shrinker *shrinker);
diff --git a/mm/Makefile b/mm/Makefile
index 678530a07326..891899186608 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -48,8 +48,8 @@ endif
 
 obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page-writeback.o folio-compat.o \
-			   readahead.o swap.o truncate.o vmscan.o shmem.o \
-			   util.o mmzone.o vmstat.o backing-dev.o \
+			   readahead.o swap.o truncate.o vmscan.o shrinker.o \
+			   shmem.o util.o mmzone.o vmstat.o backing-dev.o \
 			   mm_init.o percpu.o slab_common.o \
 			   compaction.o show_mem.o\
 			   interval_tree.o list_lru.o workingset.o \
diff --git a/mm/shrinker.c b/mm/shrinker.c
new file mode 100644
index 000000000000..0a32ef42f2a7
--- /dev/null
+++ b/mm/shrinker.c
@@ -0,0 +1,707 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/memcontrol.h>
+#include <linux/rwsem.h>
+#include <linux/shrinker.h>
+#include <trace/events/vmscan.h>
+
+LIST_HEAD(shrinker_list);
+DECLARE_RWSEM(shrinker_rwsem);
+
+#ifdef CONFIG_MEMCG
+static int shrinker_nr_max;
+
+/* The shrinker_info is expanded in a batch of BITS_PER_LONG */
+static inline int shrinker_map_size(int nr_items)
+{
+	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
+}
+
+static inline int shrinker_defer_size(int nr_items)
+{
+	return (round_up(nr_items, BITS_PER_LONG) * sizeof(atomic_long_t));
+}
+
+void free_shrinker_info(struct mem_cgroup *memcg)
+{
+	struct mem_cgroup_per_node *pn;
+	struct shrinker_info *info;
+	int nid;
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		info = rcu_dereference_protected(pn->shrinker_info, true);
+		kvfree(info);
+		rcu_assign_pointer(pn->shrinker_info, NULL);
+	}
+}
+
+int alloc_shrinker_info(struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+	int nid, size, ret = 0;
+	int map_size, defer_size = 0;
+
+	down_write(&shrinker_rwsem);
+	map_size = shrinker_map_size(shrinker_nr_max);
+	defer_size = shrinker_defer_size(shrinker_nr_max);
+	size = map_size + defer_size;
+	for_each_node(nid) {
+		info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid);
+		if (!info) {
+			free_shrinker_info(memcg);
+			ret = -ENOMEM;
+			break;
+		}
+		info->nr_deferred = (atomic_long_t *)(info + 1);
+		info->map = (void *)info->nr_deferred + defer_size;
+		info->map_nr_max = shrinker_nr_max;
+		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
+	}
+	up_write(&shrinker_rwsem);
+
+	return ret;
+}
+
+static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
+						     int nid)
+{
+	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
+					 lockdep_is_held(&shrinker_rwsem));
+}
+
+static int expand_one_shrinker_info(struct mem_cgroup *memcg,
+				    int map_size, int defer_size,
+				    int old_map_size, int old_defer_size,
+				    int new_nr_max)
+{
+	struct shrinker_info *new, *old;
+	struct mem_cgroup_per_node *pn;
+	int nid;
+	int size = map_size + defer_size;
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		old = shrinker_info_protected(memcg, nid);
+		/* Not yet online memcg */
+		if (!old)
+			return 0;
+
+		/* Already expanded this shrinker_info */
+		if (new_nr_max <= old->map_nr_max)
+			continue;
+
+		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
+		if (!new)
+			return -ENOMEM;
+
+		new->nr_deferred = (atomic_long_t *)(new + 1);
+		new->map = (void *)new->nr_deferred + defer_size;
+		new->map_nr_max = new_nr_max;
+
+		/* map: set all old bits, clear all new bits */
+		memset(new->map, (int)0xff, old_map_size);
+		memset((void *)new->map + old_map_size, 0, map_size - old_map_size);
+		/* nr_deferred: copy old values, clear all new values */
+		memcpy(new->nr_deferred, old->nr_deferred, old_defer_size);
+		memset((void *)new->nr_deferred + old_defer_size, 0,
+		       defer_size - old_defer_size);
+
+		rcu_assign_pointer(pn->shrinker_info, new);
+		kvfree_rcu(old, rcu);
+	}
+
+	return 0;
+}
+
+static int expand_shrinker_info(int new_id)
+{
+	int ret = 0;
+	int new_nr_max = round_up(new_id + 1, BITS_PER_LONG);
+	int map_size, defer_size = 0;
+	int old_map_size, old_defer_size = 0;
+	struct mem_cgroup *memcg;
+
+	if (!root_mem_cgroup)
+		goto out;
+
+	lockdep_assert_held(&shrinker_rwsem);
+
+	map_size = shrinker_map_size(new_nr_max);
+	defer_size = shrinker_defer_size(new_nr_max);
+	old_map_size = shrinker_map_size(shrinker_nr_max);
+	old_defer_size = shrinker_defer_size(shrinker_nr_max);
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		ret = expand_one_shrinker_info(memcg, map_size, defer_size,
+					       old_map_size, old_defer_size,
+					       new_nr_max);
+		if (ret) {
+			mem_cgroup_iter_break(NULL, memcg);
+			goto out;
+		}
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
+out:
+	if (!ret)
+		shrinker_nr_max = new_nr_max;
+
+	return ret;
+}
+
+void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
+{
+	if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
+		struct shrinker_info *info;
+
+		rcu_read_lock();
+		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+		if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
+			/* Pairs with smp mb in shrink_slab() */
+			smp_mb__before_atomic();
+			set_bit(shrinker_id, info->map);
+		}
+		rcu_read_unlock();
+	}
+}
+
+static DEFINE_IDR(shrinker_idr);
+
+static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+{
+	int id, ret = -ENOMEM;
+
+	if (mem_cgroup_disabled())
+		return -ENOSYS;
+
+	down_write(&shrinker_rwsem);
+	/* This may call shrinker, so it must use down_read_trylock() */
+	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
+	if (id < 0)
+		goto unlock;
+
+	if (id >= shrinker_nr_max) {
+		if (expand_shrinker_info(id)) {
+			idr_remove(&shrinker_idr, id);
+			goto unlock;
+		}
+	}
+	shrinker->id = id;
+	ret = 0;
+unlock:
+	up_write(&shrinker_rwsem);
+	return ret;
+}
+
+static void unregister_memcg_shrinker(struct shrinker *shrinker)
+{
+	int id = shrinker->id;
+
+	BUG_ON(id < 0);
+
+	lockdep_assert_held(&shrinker_rwsem);
+
+	idr_remove(&shrinker_idr, id);
+}
+
+static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
+				   struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+
+	info = shrinker_info_protected(memcg, nid);
+	return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
+}
+
+static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
+				  struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+
+	info = shrinker_info_protected(memcg, nid);
+	return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
+}
+
+void reparent_shrinker_deferred(struct mem_cgroup *memcg)
+{
+	int i, nid;
+	long nr;
+	struct mem_cgroup *parent;
+	struct shrinker_info *child_info, *parent_info;
+
+	parent = parent_mem_cgroup(memcg);
+	if (!parent)
+		parent = root_mem_cgroup;
+
+	/* Prevent from concurrent shrinker_info expand */
+	down_read(&shrinker_rwsem);
+	for_each_node(nid) {
+		child_info = shrinker_info_protected(memcg, nid);
+		parent_info = shrinker_info_protected(parent, nid);
+		for (i = 0; i < child_info->map_nr_max; i++) {
+			nr = atomic_long_read(&child_info->nr_deferred[i]);
+			atomic_long_add(nr, &parent_info->nr_deferred[i]);
+		}
+	}
+	up_read(&shrinker_rwsem);
+}
+#else
+static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+{
+	return -ENOSYS;
+}
+
+static void unregister_memcg_shrinker(struct shrinker *shrinker)
+{
+}
+
+static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
+				   struct mem_cgroup *memcg)
+{
+	return 0;
+}
+
+static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
+				  struct mem_cgroup *memcg)
+{
+	return 0;
+}
+#endif /* CONFIG_MEMCG */
+
+static long xchg_nr_deferred(struct shrinker *shrinker,
+			     struct shrink_control *sc)
+{
+	int nid = sc->nid;
+
+	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
+		nid = 0;
+
+	if (sc->memcg &&
+	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
+		return xchg_nr_deferred_memcg(nid, shrinker,
+					      sc->memcg);
+
+	return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
+}
+
+
+static long add_nr_deferred(long nr, struct shrinker *shrinker,
+			    struct shrink_control *sc)
+{
+	int nid = sc->nid;
+
+	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
+		nid = 0;
+
+	if (sc->memcg &&
+	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
+		return add_nr_deferred_memcg(nr, nid, shrinker,
+					     sc->memcg);
+
+	return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
+}
+
+#define SHRINK_BATCH 128
+
+static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
+				    struct shrinker *shrinker, int priority)
+{
+	unsigned long freed = 0;
+	unsigned long long delta;
+	long total_scan;
+	long freeable;
+	long nr;
+	long new_nr;
+	long batch_size = shrinker->batch ? shrinker->batch
+					  : SHRINK_BATCH;
+	long scanned = 0, next_deferred;
+
+	freeable = shrinker->count_objects(shrinker, shrinkctl);
+	if (freeable == 0 || freeable == SHRINK_EMPTY)
+		return freeable;
+
+	/*
+	 * copy the current shrinker scan count into a local variable
+	 * and zero it so that other concurrent shrinker invocations
+	 * don't also do this scanning work.
+	 */
+	nr = xchg_nr_deferred(shrinker, shrinkctl);
+
+	if (shrinker->seeks) {
+		delta = freeable >> priority;
+		delta *= 4;
+		do_div(delta, shrinker->seeks);
+	} else {
+		/*
+		 * These objects don't require any IO to create. Trim
+		 * them aggressively under memory pressure to keep
+		 * them from causing refetches in the IO caches.
+		 */
+		delta = freeable / 2;
+	}
+
+	total_scan = nr >> priority;
+	total_scan += delta;
+	total_scan = min(total_scan, (2 * freeable));
+
+	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
+				   freeable, delta, total_scan, priority);
+
+	/*
+	 * Normally, we should not scan less than batch_size objects in one
+	 * pass to avoid too frequent shrinker calls, but if the slab has less
+	 * than batch_size objects in total and we are really tight on memory,
+	 * we will try to reclaim all available objects, otherwise we can end
+	 * up failing allocations although there are plenty of reclaimable
+	 * objects spread over several slabs with usage less than the
+	 * batch_size.
+	 *
+	 * We detect the "tight on memory" situations by looking at the total
+	 * number of objects we want to scan (total_scan). If it is greater
+	 * than the total number of objects on slab (freeable), we must be
+	 * scanning at high prio and therefore should try to reclaim as much as
+	 * possible.
+	 */
+	while (total_scan >= batch_size ||
+	       total_scan >= freeable) {
+		unsigned long ret;
+		unsigned long nr_to_scan = min(batch_size, total_scan);
+
+		shrinkctl->nr_to_scan = nr_to_scan;
+		shrinkctl->nr_scanned = nr_to_scan;
+		ret = shrinker->scan_objects(shrinker, shrinkctl);
+		if (ret == SHRINK_STOP)
+			break;
+		freed += ret;
+
+		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
+		total_scan -= shrinkctl->nr_scanned;
+		scanned += shrinkctl->nr_scanned;
+
+		cond_resched();
+	}
+
+	/*
+	 * The deferred work is increased by any new work (delta) that wasn't
+	 * done, decreased by old deferred work that was done now.
+	 *
+	 * And it is capped to two times of the freeable items.
+	 */
+	next_deferred = max_t(long, (nr + delta - scanned), 0);
+	next_deferred = min(next_deferred, (2 * freeable));
+
+	/*
+	 * move the unused scan count back into the shrinker in a
+	 * manner that handles concurrent updates.
+	 */
+	new_nr = add_nr_deferred(next_deferred, shrinker, shrinkctl);
+
+	trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
+	return freed;
+}
+
+#ifdef CONFIG_MEMCG
+static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
+			struct mem_cgroup *memcg, int priority)
+{
+	struct shrinker_info *info;
+	unsigned long ret, freed = 0;
+	int i;
+
+	if (!mem_cgroup_online(memcg))
+		return 0;
+
+	if (!down_read_trylock(&shrinker_rwsem))
+		return 0;
+
+	info = shrinker_info_protected(memcg, nid);
+	if (unlikely(!info))
+		goto unlock;
+
+	for_each_set_bit(i, info->map, info->map_nr_max) {
+		struct shrink_control sc = {
+			.gfp_mask = gfp_mask,
+			.nid = nid,
+			.memcg = memcg,
+		};
+		struct shrinker *shrinker;
+
+		shrinker = idr_find(&shrinker_idr, i);
+		if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
+			if (!shrinker)
+				clear_bit(i, info->map);
+			continue;
+		}
+
+		/* Call non-slab shrinkers even though kmem is disabled */
+		if (!memcg_kmem_online() &&
+		    !(shrinker->flags & SHRINKER_NONSLAB))
+			continue;
+
+		ret = do_shrink_slab(&sc, shrinker, priority);
+		if (ret == SHRINK_EMPTY) {
+			clear_bit(i, info->map);
+			/*
+			 * After the shrinker reported that it had no objects to
+			 * free, but before we cleared the corresponding bit in
+			 * the memcg shrinker map, a new object might have been
+			 * added. To make sure, we have the bit set in this
+			 * case, we invoke the shrinker one more time and reset
+			 * the bit if it reports that it is not empty anymore.
+			 * The memory barrier here pairs with the barrier in
+			 * set_shrinker_bit():
+			 *
+			 * list_lru_add()     shrink_slab_memcg()
+			 *   list_add_tail()    clear_bit()
+			 *   <MB>               <MB>
+			 *   set_bit()          do_shrink_slab()
+			 */
+			smp_mb__after_atomic();
+			ret = do_shrink_slab(&sc, shrinker, priority);
+			if (ret == SHRINK_EMPTY)
+				ret = 0;
+			else
+				set_shrinker_bit(memcg, nid, i);
+		}
+		freed += ret;
+
+		if (rwsem_is_contended(&shrinker_rwsem)) {
+			freed = freed ? : 1;
+			break;
+		}
+	}
+unlock:
+	up_read(&shrinker_rwsem);
+	return freed;
+}
+#else /* !CONFIG_MEMCG */
+static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
+			struct mem_cgroup *memcg, int priority)
+{
+	return 0;
+}
+#endif /* CONFIG_MEMCG */
+
+/**
+ * shrink_slab - shrink slab caches
+ * @gfp_mask: allocation context
+ * @nid: node whose slab caches to target
+ * @memcg: memory cgroup whose slab caches to target
+ * @priority: the reclaim priority
+ *
+ * Call the shrink functions to age shrinkable caches.
+ *
+ * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
+ * unaware shrinkers will receive a node id of 0 instead.
+ *
+ * @memcg specifies the memory cgroup to target. Unaware shrinkers
+ * are called only if it is the root cgroup.
+ *
+ * @priority is sc->priority, we take the number of objects and >> by priority
+ * in order to get the scan target.
+ *
+ * Returns the number of reclaimed slab objects.
+ */
+unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
+			  int priority)
+{
+	unsigned long ret, freed = 0;
+	struct shrinker *shrinker;
+
+	/*
+	 * The root memcg might be allocated even though memcg is disabled
+	 * via "cgroup_disable=memory" boot parameter.  This could make
+	 * mem_cgroup_is_root() return false, then just run memcg slab
+	 * shrink, but skip global shrink.  This may result in premature
+	 * oom.
+	 */
+	if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
+		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
+
+	if (!down_read_trylock(&shrinker_rwsem))
+		goto out;
+
+	list_for_each_entry(shrinker, &shrinker_list, list) {
+		struct shrink_control sc = {
+			.gfp_mask = gfp_mask,
+			.nid = nid,
+			.memcg = memcg,
+		};
+
+		ret = do_shrink_slab(&sc, shrinker, priority);
+		if (ret == SHRINK_EMPTY)
+			ret = 0;
+		freed += ret;
+		/*
+		 * Bail out if someone want to register a new shrinker to
+		 * prevent the registration from being stalled for long periods
+		 * by parallel ongoing shrinking.
+		 */
+		if (rwsem_is_contended(&shrinker_rwsem)) {
+			freed = freed ? : 1;
+			break;
+		}
+	}
+
+	up_read(&shrinker_rwsem);
+out:
+	cond_resched();
+	return freed;
+}
+
+/*
+ * Add a shrinker callback to be called from the vm.
+ */
+static int __prealloc_shrinker(struct shrinker *shrinker)
+{
+	unsigned int size;
+	int err;
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+		err = prealloc_memcg_shrinker(shrinker);
+		if (err != -ENOSYS)
+			return err;
+
+		shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
+	}
+
+	size = sizeof(*shrinker->nr_deferred);
+	if (shrinker->flags & SHRINKER_NUMA_AWARE)
+		size *= nr_node_ids;
+
+	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
+	if (!shrinker->nr_deferred)
+		return -ENOMEM;
+
+	return 0;
+}
+
+#ifdef CONFIG_SHRINKER_DEBUG
+int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	va_list ap;
+	int err;
+
+	va_start(ap, fmt);
+	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
+	va_end(ap);
+	if (!shrinker->name)
+		return -ENOMEM;
+
+	err = __prealloc_shrinker(shrinker);
+	if (err) {
+		kfree_const(shrinker->name);
+		shrinker->name = NULL;
+	}
+
+	return err;
+}
+#else
+int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	return __prealloc_shrinker(shrinker);
+}
+#endif
+
+void free_prealloced_shrinker(struct shrinker *shrinker)
+{
+#ifdef CONFIG_SHRINKER_DEBUG
+	kfree_const(shrinker->name);
+	shrinker->name = NULL;
+#endif
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+		down_write(&shrinker_rwsem);
+		unregister_memcg_shrinker(shrinker);
+		up_write(&shrinker_rwsem);
+		return;
+	}
+
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+}
+
+void register_shrinker_prepared(struct shrinker *shrinker)
+{
+	down_write(&shrinker_rwsem);
+	list_add_tail(&shrinker->list, &shrinker_list);
+	shrinker->flags |= SHRINKER_REGISTERED;
+	shrinker_debugfs_add(shrinker);
+	up_write(&shrinker_rwsem);
+}
+
+static int __register_shrinker(struct shrinker *shrinker)
+{
+	int err = __prealloc_shrinker(shrinker);
+
+	if (err)
+		return err;
+	register_shrinker_prepared(shrinker);
+	return 0;
+}
+
+#ifdef CONFIG_SHRINKER_DEBUG
+int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	va_list ap;
+	int err;
+
+	va_start(ap, fmt);
+	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
+	va_end(ap);
+	if (!shrinker->name)
+		return -ENOMEM;
+
+	err = __register_shrinker(shrinker);
+	if (err) {
+		kfree_const(shrinker->name);
+		shrinker->name = NULL;
+	}
+	return err;
+}
+#else
+int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
+{
+	return __register_shrinker(shrinker);
+}
+#endif
+EXPORT_SYMBOL(register_shrinker);
+
+/*
+ * Remove one
+ */
+void unregister_shrinker(struct shrinker *shrinker)
+{
+	struct dentry *debugfs_entry;
+	int debugfs_id;
+
+	if (!(shrinker->flags & SHRINKER_REGISTERED))
+		return;
+
+	down_write(&shrinker_rwsem);
+	list_del(&shrinker->list);
+	shrinker->flags &= ~SHRINKER_REGISTERED;
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
+	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
+	up_write(&shrinker_rwsem);
+
+	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
+
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+}
+EXPORT_SYMBOL(unregister_shrinker);
+
+/**
+ * synchronize_shrinkers - Wait for all running shrinkers to complete.
+ *
+ * This is equivalent to calling unregister_shrink() and register_shrinker(),
+ * but atomically and with less overhead. This is useful to guarantee that all
+ * shrinker invocations have seen an update, before freeing memory, similar to
+ * rcu.
+ */
+void synchronize_shrinkers(void)
+{
+	down_write(&shrinker_rwsem);
+	up_write(&shrinker_rwsem);
+}
+EXPORT_SYMBOL(synchronize_shrinkers);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4039620d30fe..07bc58af6f26 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -35,7 +35,6 @@
 #include <linux/cpuset.h>
 #include <linux/compaction.h>
 #include <linux/notifier.h>
-#include <linux/rwsem.h>
 #include <linux/delay.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
@@ -188,246 +187,7 @@ struct scan_control {
  */
 int vm_swappiness = 60;
 
-LIST_HEAD(shrinker_list);
-DECLARE_RWSEM(shrinker_rwsem);
-
 #ifdef CONFIG_MEMCG
-static int shrinker_nr_max;
-
-/* The shrinker_info is expanded in a batch of BITS_PER_LONG */
-static inline int shrinker_map_size(int nr_items)
-{
-	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
-}
-
-static inline int shrinker_defer_size(int nr_items)
-{
-	return (round_up(nr_items, BITS_PER_LONG) * sizeof(atomic_long_t));
-}
-
-static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
-						     int nid)
-{
-	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
-					 lockdep_is_held(&shrinker_rwsem));
-}
-
-static int expand_one_shrinker_info(struct mem_cgroup *memcg,
-				    int map_size, int defer_size,
-				    int old_map_size, int old_defer_size,
-				    int new_nr_max)
-{
-	struct shrinker_info *new, *old;
-	struct mem_cgroup_per_node *pn;
-	int nid;
-	int size = map_size + defer_size;
-
-	for_each_node(nid) {
-		pn = memcg->nodeinfo[nid];
-		old = shrinker_info_protected(memcg, nid);
-		/* Not yet online memcg */
-		if (!old)
-			return 0;
-
-		/* Already expanded this shrinker_info */
-		if (new_nr_max <= old->map_nr_max)
-			continue;
-
-		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
-		if (!new)
-			return -ENOMEM;
-
-		new->nr_deferred = (atomic_long_t *)(new + 1);
-		new->map = (void *)new->nr_deferred + defer_size;
-		new->map_nr_max = new_nr_max;
-
-		/* map: set all old bits, clear all new bits */
-		memset(new->map, (int)0xff, old_map_size);
-		memset((void *)new->map + old_map_size, 0, map_size - old_map_size);
-		/* nr_deferred: copy old values, clear all new values */
-		memcpy(new->nr_deferred, old->nr_deferred, old_defer_size);
-		memset((void *)new->nr_deferred + old_defer_size, 0,
-		       defer_size - old_defer_size);
-
-		rcu_assign_pointer(pn->shrinker_info, new);
-		kvfree_rcu(old, rcu);
-	}
-
-	return 0;
-}
-
-void free_shrinker_info(struct mem_cgroup *memcg)
-{
-	struct mem_cgroup_per_node *pn;
-	struct shrinker_info *info;
-	int nid;
-
-	for_each_node(nid) {
-		pn = memcg->nodeinfo[nid];
-		info = rcu_dereference_protected(pn->shrinker_info, true);
-		kvfree(info);
-		rcu_assign_pointer(pn->shrinker_info, NULL);
-	}
-}
-
-int alloc_shrinker_info(struct mem_cgroup *memcg)
-{
-	struct shrinker_info *info;
-	int nid, size, ret = 0;
-	int map_size, defer_size = 0;
-
-	down_write(&shrinker_rwsem);
-	map_size = shrinker_map_size(shrinker_nr_max);
-	defer_size = shrinker_defer_size(shrinker_nr_max);
-	size = map_size + defer_size;
-	for_each_node(nid) {
-		info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid);
-		if (!info) {
-			free_shrinker_info(memcg);
-			ret = -ENOMEM;
-			break;
-		}
-		info->nr_deferred = (atomic_long_t *)(info + 1);
-		info->map = (void *)info->nr_deferred + defer_size;
-		info->map_nr_max = shrinker_nr_max;
-		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
-	}
-	up_write(&shrinker_rwsem);
-
-	return ret;
-}
-
-static int expand_shrinker_info(int new_id)
-{
-	int ret = 0;
-	int new_nr_max = round_up(new_id + 1, BITS_PER_LONG);
-	int map_size, defer_size = 0;
-	int old_map_size, old_defer_size = 0;
-	struct mem_cgroup *memcg;
-
-	if (!root_mem_cgroup)
-		goto out;
-
-	lockdep_assert_held(&shrinker_rwsem);
-
-	map_size = shrinker_map_size(new_nr_max);
-	defer_size = shrinker_defer_size(new_nr_max);
-	old_map_size = shrinker_map_size(shrinker_nr_max);
-	old_defer_size = shrinker_defer_size(shrinker_nr_max);
-
-	memcg = mem_cgroup_iter(NULL, NULL, NULL);
-	do {
-		ret = expand_one_shrinker_info(memcg, map_size, defer_size,
-					       old_map_size, old_defer_size,
-					       new_nr_max);
-		if (ret) {
-			mem_cgroup_iter_break(NULL, memcg);
-			goto out;
-		}
-	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
-out:
-	if (!ret)
-		shrinker_nr_max = new_nr_max;
-
-	return ret;
-}
-
-void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
-{
-	if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
-		struct shrinker_info *info;
-
-		rcu_read_lock();
-		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
-		if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
-			/* Pairs with smp mb in shrink_slab() */
-			smp_mb__before_atomic();
-			set_bit(shrinker_id, info->map);
-		}
-		rcu_read_unlock();
-	}
-}
-
-static DEFINE_IDR(shrinker_idr);
-
-static int prealloc_memcg_shrinker(struct shrinker *shrinker)
-{
-	int id, ret = -ENOMEM;
-
-	if (mem_cgroup_disabled())
-		return -ENOSYS;
-
-	down_write(&shrinker_rwsem);
-	/* This may call shrinker, so it must use down_read_trylock() */
-	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
-	if (id < 0)
-		goto unlock;
-
-	if (id >= shrinker_nr_max) {
-		if (expand_shrinker_info(id)) {
-			idr_remove(&shrinker_idr, id);
-			goto unlock;
-		}
-	}
-	shrinker->id = id;
-	ret = 0;
-unlock:
-	up_write(&shrinker_rwsem);
-	return ret;
-}
-
-static void unregister_memcg_shrinker(struct shrinker *shrinker)
-{
-	int id = shrinker->id;
-
-	BUG_ON(id < 0);
-
-	lockdep_assert_held(&shrinker_rwsem);
-
-	idr_remove(&shrinker_idr, id);
-}
-
-static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
-				   struct mem_cgroup *memcg)
-{
-	struct shrinker_info *info;
-
-	info = shrinker_info_protected(memcg, nid);
-	return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
-}
-
-static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
-				  struct mem_cgroup *memcg)
-{
-	struct shrinker_info *info;
-
-	info = shrinker_info_protected(memcg, nid);
-	return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
-}
-
-void reparent_shrinker_deferred(struct mem_cgroup *memcg)
-{
-	int i, nid;
-	long nr;
-	struct mem_cgroup *parent;
-	struct shrinker_info *child_info, *parent_info;
-
-	parent = parent_mem_cgroup(memcg);
-	if (!parent)
-		parent = root_mem_cgroup;
-
-	/* Prevent from concurrent shrinker_info expand */
-	down_read(&shrinker_rwsem);
-	for_each_node(nid) {
-		child_info = shrinker_info_protected(memcg, nid);
-		parent_info = shrinker_info_protected(parent, nid);
-		for (i = 0; i < child_info->map_nr_max; i++) {
-			nr = atomic_long_read(&child_info->nr_deferred[i]);
-			atomic_long_add(nr, &parent_info->nr_deferred[i]);
-		}
-	}
-	up_read(&shrinker_rwsem);
-}
 
 /* Returns true for reclaim through cgroup limits or cgroup interfaces. */
 static bool cgroup_reclaim(struct scan_control *sc)
@@ -468,27 +228,6 @@ static bool writeback_throttling_sane(struct scan_control *sc)
 	return false;
 }
 #else
-static int prealloc_memcg_shrinker(struct shrinker *shrinker)
-{
-	return -ENOSYS;
-}
-
-static void unregister_memcg_shrinker(struct shrinker *shrinker)
-{
-}
-
-static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
-				   struct mem_cgroup *memcg)
-{
-	return 0;
-}
-
-static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
-				  struct mem_cgroup *memcg)
-{
-	return 0;
-}
-
 static bool cgroup_reclaim(struct scan_control *sc)
 {
 	return false;
@@ -557,39 +296,6 @@ static void flush_reclaim_state(struct scan_control *sc)
 	}
 }
 
-static long xchg_nr_deferred(struct shrinker *shrinker,
-			     struct shrink_control *sc)
-{
-	int nid = sc->nid;
-
-	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
-		nid = 0;
-
-	if (sc->memcg &&
-	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
-		return xchg_nr_deferred_memcg(nid, shrinker,
-					      sc->memcg);
-
-	return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
-}
-
-
-static long add_nr_deferred(long nr, struct shrinker *shrinker,
-			    struct shrink_control *sc)
-{
-	int nid = sc->nid;
-
-	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
-		nid = 0;
-
-	if (sc->memcg &&
-	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
-		return add_nr_deferred_memcg(nr, nid, shrinker,
-					     sc->memcg);
-
-	return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
-}
-
 static bool can_demote(int nid, struct scan_control *sc)
 {
 	if (!numa_demotion_enabled)
@@ -671,413 +377,6 @@ static unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru,
 	return size;
 }
 
-/*
- * Add a shrinker callback to be called from the vm.
- */
-static int __prealloc_shrinker(struct shrinker *shrinker)
-{
-	unsigned int size;
-	int err;
-
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
-		err = prealloc_memcg_shrinker(shrinker);
-		if (err != -ENOSYS)
-			return err;
-
-		shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
-	}
-
-	size = sizeof(*shrinker->nr_deferred);
-	if (shrinker->flags & SHRINKER_NUMA_AWARE)
-		size *= nr_node_ids;
-
-	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
-	if (!shrinker->nr_deferred)
-		return -ENOMEM;
-
-	return 0;
-}
-
-#ifdef CONFIG_SHRINKER_DEBUG
-int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	va_list ap;
-	int err;
-
-	va_start(ap, fmt);
-	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
-	va_end(ap);
-	if (!shrinker->name)
-		return -ENOMEM;
-
-	err = __prealloc_shrinker(shrinker);
-	if (err) {
-		kfree_const(shrinker->name);
-		shrinker->name = NULL;
-	}
-
-	return err;
-}
-#else
-int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	return __prealloc_shrinker(shrinker);
-}
-#endif
-
-void free_prealloced_shrinker(struct shrinker *shrinker)
-{
-#ifdef CONFIG_SHRINKER_DEBUG
-	kfree_const(shrinker->name);
-	shrinker->name = NULL;
-#endif
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
-		down_write(&shrinker_rwsem);
-		unregister_memcg_shrinker(shrinker);
-		up_write(&shrinker_rwsem);
-		return;
-	}
-
-	kfree(shrinker->nr_deferred);
-	shrinker->nr_deferred = NULL;
-}
-
-void register_shrinker_prepared(struct shrinker *shrinker)
-{
-	down_write(&shrinker_rwsem);
-	list_add_tail(&shrinker->list, &shrinker_list);
-	shrinker->flags |= SHRINKER_REGISTERED;
-	shrinker_debugfs_add(shrinker);
-	up_write(&shrinker_rwsem);
-}
-
-static int __register_shrinker(struct shrinker *shrinker)
-{
-	int err = __prealloc_shrinker(shrinker);
-
-	if (err)
-		return err;
-	register_shrinker_prepared(shrinker);
-	return 0;
-}
-
-#ifdef CONFIG_SHRINKER_DEBUG
-int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	va_list ap;
-	int err;
-
-	va_start(ap, fmt);
-	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
-	va_end(ap);
-	if (!shrinker->name)
-		return -ENOMEM;
-
-	err = __register_shrinker(shrinker);
-	if (err) {
-		kfree_const(shrinker->name);
-		shrinker->name = NULL;
-	}
-	return err;
-}
-#else
-int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	return __register_shrinker(shrinker);
-}
-#endif
-EXPORT_SYMBOL(register_shrinker);
-
-/*
- * Remove one
- */
-void unregister_shrinker(struct shrinker *shrinker)
-{
-	struct dentry *debugfs_entry;
-	int debugfs_id;
-
-	if (!(shrinker->flags & SHRINKER_REGISTERED))
-		return;
-
-	down_write(&shrinker_rwsem);
-	list_del(&shrinker->list);
-	shrinker->flags &= ~SHRINKER_REGISTERED;
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		unregister_memcg_shrinker(shrinker);
-	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
-	up_write(&shrinker_rwsem);
-
-	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
-
-	kfree(shrinker->nr_deferred);
-	shrinker->nr_deferred = NULL;
-}
-EXPORT_SYMBOL(unregister_shrinker);
-
-/**
- * synchronize_shrinkers - Wait for all running shrinkers to complete.
- *
- * This is equivalent to calling unregister_shrink() and register_shrinker(),
- * but atomically and with less overhead. This is useful to guarantee that all
- * shrinker invocations have seen an update, before freeing memory, similar to
- * rcu.
- */
-void synchronize_shrinkers(void)
-{
-	down_write(&shrinker_rwsem);
-	up_write(&shrinker_rwsem);
-}
-EXPORT_SYMBOL(synchronize_shrinkers);
-
-#define SHRINK_BATCH 128
-
-static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
-				    struct shrinker *shrinker, int priority)
-{
-	unsigned long freed = 0;
-	unsigned long long delta;
-	long total_scan;
-	long freeable;
-	long nr;
-	long new_nr;
-	long batch_size = shrinker->batch ? shrinker->batch
-					  : SHRINK_BATCH;
-	long scanned = 0, next_deferred;
-
-	freeable = shrinker->count_objects(shrinker, shrinkctl);
-	if (freeable == 0 || freeable == SHRINK_EMPTY)
-		return freeable;
-
-	/*
-	 * copy the current shrinker scan count into a local variable
-	 * and zero it so that other concurrent shrinker invocations
-	 * don't also do this scanning work.
-	 */
-	nr = xchg_nr_deferred(shrinker, shrinkctl);
-
-	if (shrinker->seeks) {
-		delta = freeable >> priority;
-		delta *= 4;
-		do_div(delta, shrinker->seeks);
-	} else {
-		/*
-		 * These objects don't require any IO to create. Trim
-		 * them aggressively under memory pressure to keep
-		 * them from causing refetches in the IO caches.
-		 */
-		delta = freeable / 2;
-	}
-
-	total_scan = nr >> priority;
-	total_scan += delta;
-	total_scan = min(total_scan, (2 * freeable));
-
-	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
-				   freeable, delta, total_scan, priority);
-
-	/*
-	 * Normally, we should not scan less than batch_size objects in one
-	 * pass to avoid too frequent shrinker calls, but if the slab has less
-	 * than batch_size objects in total and we are really tight on memory,
-	 * we will try to reclaim all available objects, otherwise we can end
-	 * up failing allocations although there are plenty of reclaimable
-	 * objects spread over several slabs with usage less than the
-	 * batch_size.
-	 *
-	 * We detect the "tight on memory" situations by looking at the total
-	 * number of objects we want to scan (total_scan). If it is greater
-	 * than the total number of objects on slab (freeable), we must be
-	 * scanning at high prio and therefore should try to reclaim as much as
-	 * possible.
-	 */
-	while (total_scan >= batch_size ||
-	       total_scan >= freeable) {
-		unsigned long ret;
-		unsigned long nr_to_scan = min(batch_size, total_scan);
-
-		shrinkctl->nr_to_scan = nr_to_scan;
-		shrinkctl->nr_scanned = nr_to_scan;
-		ret = shrinker->scan_objects(shrinker, shrinkctl);
-		if (ret == SHRINK_STOP)
-			break;
-		freed += ret;
-
-		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
-		total_scan -= shrinkctl->nr_scanned;
-		scanned += shrinkctl->nr_scanned;
-
-		cond_resched();
-	}
-
-	/*
-	 * The deferred work is increased by any new work (delta) that wasn't
-	 * done, decreased by old deferred work that was done now.
-	 *
-	 * And it is capped to two times of the freeable items.
-	 */
-	next_deferred = max_t(long, (nr + delta - scanned), 0);
-	next_deferred = min(next_deferred, (2 * freeable));
-
-	/*
-	 * move the unused scan count back into the shrinker in a
-	 * manner that handles concurrent updates.
-	 */
-	new_nr = add_nr_deferred(next_deferred, shrinker, shrinkctl);
-
-	trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
-	return freed;
-}
-
-#ifdef CONFIG_MEMCG
-static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
-			struct mem_cgroup *memcg, int priority)
-{
-	struct shrinker_info *info;
-	unsigned long ret, freed = 0;
-	int i;
-
-	if (!mem_cgroup_online(memcg))
-		return 0;
-
-	if (!down_read_trylock(&shrinker_rwsem))
-		return 0;
-
-	info = shrinker_info_protected(memcg, nid);
-	if (unlikely(!info))
-		goto unlock;
-
-	for_each_set_bit(i, info->map, info->map_nr_max) {
-		struct shrink_control sc = {
-			.gfp_mask = gfp_mask,
-			.nid = nid,
-			.memcg = memcg,
-		};
-		struct shrinker *shrinker;
-
-		shrinker = idr_find(&shrinker_idr, i);
-		if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
-			if (!shrinker)
-				clear_bit(i, info->map);
-			continue;
-		}
-
-		/* Call non-slab shrinkers even though kmem is disabled */
-		if (!memcg_kmem_online() &&
-		    !(shrinker->flags & SHRINKER_NONSLAB))
-			continue;
-
-		ret = do_shrink_slab(&sc, shrinker, priority);
-		if (ret == SHRINK_EMPTY) {
-			clear_bit(i, info->map);
-			/*
-			 * After the shrinker reported that it had no objects to
-			 * free, but before we cleared the corresponding bit in
-			 * the memcg shrinker map, a new object might have been
-			 * added. To make sure, we have the bit set in this
-			 * case, we invoke the shrinker one more time and reset
-			 * the bit if it reports that it is not empty anymore.
-			 * The memory barrier here pairs with the barrier in
-			 * set_shrinker_bit():
-			 *
-			 * list_lru_add()     shrink_slab_memcg()
-			 *   list_add_tail()    clear_bit()
-			 *   <MB>               <MB>
-			 *   set_bit()          do_shrink_slab()
-			 */
-			smp_mb__after_atomic();
-			ret = do_shrink_slab(&sc, shrinker, priority);
-			if (ret == SHRINK_EMPTY)
-				ret = 0;
-			else
-				set_shrinker_bit(memcg, nid, i);
-		}
-		freed += ret;
-
-		if (rwsem_is_contended(&shrinker_rwsem)) {
-			freed = freed ? : 1;
-			break;
-		}
-	}
-unlock:
-	up_read(&shrinker_rwsem);
-	return freed;
-}
-#else /* CONFIG_MEMCG */
-static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
-			struct mem_cgroup *memcg, int priority)
-{
-	return 0;
-}
-#endif /* CONFIG_MEMCG */
-
-/**
- * shrink_slab - shrink slab caches
- * @gfp_mask: allocation context
- * @nid: node whose slab caches to target
- * @memcg: memory cgroup whose slab caches to target
- * @priority: the reclaim priority
- *
- * Call the shrink functions to age shrinkable caches.
- *
- * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
- * unaware shrinkers will receive a node id of 0 instead.
- *
- * @memcg specifies the memory cgroup to target. Unaware shrinkers
- * are called only if it is the root cgroup.
- *
- * @priority is sc->priority, we take the number of objects and >> by priority
- * in order to get the scan target.
- *
- * Returns the number of reclaimed slab objects.
- */
-static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
-				 struct mem_cgroup *memcg,
-				 int priority)
-{
-	unsigned long ret, freed = 0;
-	struct shrinker *shrinker;
-
-	/*
-	 * The root memcg might be allocated even though memcg is disabled
-	 * via "cgroup_disable=memory" boot parameter.  This could make
-	 * mem_cgroup_is_root() return false, then just run memcg slab
-	 * shrink, but skip global shrink.  This may result in premature
-	 * oom.
-	 */
-	if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
-		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
-
-	if (!down_read_trylock(&shrinker_rwsem))
-		goto out;
-
-	list_for_each_entry(shrinker, &shrinker_list, list) {
-		struct shrink_control sc = {
-			.gfp_mask = gfp_mask,
-			.nid = nid,
-			.memcg = memcg,
-		};
-
-		ret = do_shrink_slab(&sc, shrinker, priority);
-		if (ret == SHRINK_EMPTY)
-			ret = 0;
-		freed += ret;
-		/*
-		 * Bail out if someone want to register a new shrinker to
-		 * prevent the registration from being stalled for long periods
-		 * by parallel ongoing shrinking.
-		 */
-		if (rwsem_is_contended(&shrinker_rwsem)) {
-			freed = freed ? : 1;
-			break;
-		}
-	}
-
-	up_read(&shrinker_rwsem);
-out:
-	cond_resched();
-	return freed;
-}
-
 static unsigned long drop_slab_node(int nid)
 {
 	unsigned long freed = 0;
-- 
2.30.2

[PATCH v2 02/47] mm: shrinker: remove redundant shrinker_rwsem in debugfs operations

[Qi Zheng]

The debugfs_remove_recursive() will wait for debugfs_file_put() to return,
so the shrinker will not be freed when doing debugfs operations (such as
shrinker_debugfs_count_show() and shrinker_debugfs_scan_write()), so there
is no need to hold shrinker_rwsem during debugfs operations.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/shrinker_debug.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 3ab53fad8876..f1becfd45853 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -55,11 +55,6 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
 	if (!count_per_node)
 		return -ENOMEM;
 
-	ret = down_read_killable(&shrinker_rwsem);
-	if (ret) {
-		kfree(count_per_node);
-		return ret;
-	}
 	rcu_read_lock();
 
 	memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;
@@ -92,7 +87,6 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
 	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 
 	rcu_read_unlock();
-	up_read(&shrinker_rwsem);
 
 	kfree(count_per_node);
 	return ret;
@@ -117,7 +111,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 	struct mem_cgroup *memcg = NULL;
 	int nid;
 	char kbuf[72];
-	ssize_t ret;
 
 	read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
 	if (copy_from_user(kbuf, buf, read_len))
@@ -146,12 +139,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 		return -EINVAL;
 	}
 
-	ret = down_read_killable(&shrinker_rwsem);
-	if (ret) {
-		mem_cgroup_put(memcg);
-		return ret;
-	}
-
 	sc.nid = nid;
 	sc.memcg = memcg;
 	sc.nr_to_scan = nr_to_scan;
@@ -159,7 +146,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
 
 	shrinker->scan_objects(shrinker, &sc);
 
-	up_read(&shrinker_rwsem);
 	mem_cgroup_put(memcg);
 
 	return size;
-- 
2.30.2

[PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Qi Zheng]

Currently, the shrinker instances can be divided into the following three
types:

a) global shrinker instance statically defined in the kernel, such as
   workingset_shadow_shrinker.

b) global shrinker instance statically defined in the kernel modules, such
   as mmu_shrinker in x86.

c) shrinker instance embedded in other structures.

For case a, the memory of shrinker instance is never freed. For case b,
the memory of shrinker instance will be freed after synchronize_rcu() when
the module is unloaded. For case c, the memory of shrinker instance will
be freed along with the structure it is embedded in.

In preparation for implementing lockless slab shrink, we need to
dynamically allocate those shrinker instances in case c, then the memory
can be dynamically freed alone by calling kfree_rcu().

So this commit adds the following new APIs for dynamically allocating
shrinker, and add a private_data field to struct shrinker to record and
get the original embedded structure.

1. shrinker_alloc()

Used to allocate shrinker instance itself and related memory, it will
return a pointer to the shrinker instance on success and NULL on failure.

2. shrinker_free_non_registered()

Used to destroy the non-registered shrinker instance.

3. shrinker_register()

Used to register the shrinker instance, which is same as the current
register_shrinker_prepared().

4. shrinker_unregister()

Used to unregister and free the shrinker instance.

In order to simplify shrinker-related APIs and make shrinker more
independent of other kernel mechanisms, subsequent submissions will use
the above API to convert all shrinkers (including case a and b) to
dynamically allocated, and then remove all existing APIs.

This will also have another advantage mentioned by Dave Chinner:

```
The other advantage of this is that it will break all the existing
out of tree code and third party modules using the old API and will
no longer work with a kernel using lockless slab shrinkers. They
need to break (both at the source and binary levels) to stop bad
things from happening due to using uncoverted shrinkers in the new
setup.
```

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 include/linux/shrinker.h |   6 +++
 mm/shrinker.c            | 113 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 961cb84e51f5..296f5e163861 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -70,6 +70,8 @@ struct shrinker {
 	int seeks;	/* seeks to recreate an obj */
 	unsigned flags;
 
+	void *private_data;
+
 	/* These are for internal use */
 	struct list_head list;
 #ifdef CONFIG_MEMCG
@@ -98,6 +100,10 @@ struct shrinker {
 
 unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
 			  int priority);
+struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...);
+void shrinker_free_non_registered(struct shrinker *shrinker);
+void shrinker_register(struct shrinker *shrinker);
+void shrinker_unregister(struct shrinker *shrinker);
 
 extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
 					    const char *fmt, ...);
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 0a32ef42f2a7..d820e4cc5806 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -548,6 +548,119 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
 	return freed;
 }
 
+struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...)
+{
+	struct shrinker *shrinker;
+	unsigned int size;
+	va_list __maybe_unused ap;
+	int err;
+
+	shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL);
+	if (!shrinker)
+		return NULL;
+
+#ifdef CONFIG_SHRINKER_DEBUG
+	va_start(ap, fmt);
+	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
+	va_end(ap);
+	if (!shrinker->name)
+		goto err_name;
+#endif
+	shrinker->flags = flags;
+
+	if (flags & SHRINKER_MEMCG_AWARE) {
+		err = prealloc_memcg_shrinker(shrinker);
+		if (err == -ENOSYS)
+			shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
+		else if (err == 0)
+			goto done;
+		else
+			goto err_flags;
+	}
+
+	/*
+	 * The nr_deferred is available on per memcg level for memcg aware
+	 * shrinkers, so only allocate nr_deferred in the following cases:
+	 *  - non memcg aware shrinkers
+	 *  - !CONFIG_MEMCG
+	 *  - memcg is disabled by kernel command line
+	 */
+	size = sizeof(*shrinker->nr_deferred);
+	if (flags & SHRINKER_NUMA_AWARE)
+		size *= nr_node_ids;
+
+	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
+	if (!shrinker->nr_deferred)
+		goto err_flags;
+
+done:
+	return shrinker;
+
+err_flags:
+#ifdef CONFIG_SHRINKER_DEBUG
+	kfree_const(shrinker->name);
+	shrinker->name = NULL;
+err_name:
+#endif
+	kfree(shrinker);
+	return NULL;
+}
+EXPORT_SYMBOL(shrinker_alloc);
+
+void shrinker_free_non_registered(struct shrinker *shrinker)
+{
+#ifdef CONFIG_SHRINKER_DEBUG
+	kfree_const(shrinker->name);
+	shrinker->name = NULL;
+#endif
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+		down_write(&shrinker_rwsem);
+		unregister_memcg_shrinker(shrinker);
+		up_write(&shrinker_rwsem);
+	}
+
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+
+	kfree(shrinker);
+}
+EXPORT_SYMBOL(shrinker_free_non_registered);
+
+void shrinker_register(struct shrinker *shrinker)
+{
+	down_write(&shrinker_rwsem);
+	list_add_tail(&shrinker->list, &shrinker_list);
+	shrinker->flags |= SHRINKER_REGISTERED;
+	shrinker_debugfs_add(shrinker);
+	up_write(&shrinker_rwsem);
+}
+EXPORT_SYMBOL(shrinker_register);
+
+void shrinker_unregister(struct shrinker *shrinker)
+{
+	struct dentry *debugfs_entry;
+	int debugfs_id;
+
+	if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))
+		return;
+
+	down_write(&shrinker_rwsem);
+	list_del(&shrinker->list);
+	shrinker->flags &= ~SHRINKER_REGISTERED;
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
+	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
+	up_write(&shrinker_rwsem);
+
+	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
+
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+
+	kfree(shrinker);
+}
+EXPORT_SYMBOL(shrinker_unregister);
+
 /*
  * Add a shrinker callback to be called from the vm.
  */
-- 
2.30.2

[PATCH v2 04/47] kvm: mmu: dynamically allocate the x86-mmu shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the x86-mmu shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 arch/x86/kvm/mmu/mmu.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index ec169f5c7dce..ab405e0a8954 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6847,11 +6847,7 @@ static unsigned long mmu_shrink_count(struct shrinker *shrink,
 	return percpu_counter_read_positive(&kvm_total_used_mmu_pages);
 }
 
-static struct shrinker mmu_shrinker = {
-	.count_objects = mmu_shrink_count,
-	.scan_objects = mmu_shrink_scan,
-	.seeks = DEFAULT_SEEKS * 10,
-};
+static struct shrinker *mmu_shrinker;
 
 static void mmu_destroy_caches(void)
 {
@@ -6984,10 +6980,16 @@ int kvm_mmu_vendor_module_init(void)
 	if (percpu_counter_init(&kvm_total_used_mmu_pages, 0, GFP_KERNEL))
 		goto out;
 
-	ret = register_shrinker(&mmu_shrinker, "x86-mmu");
-	if (ret)
+	mmu_shrinker = shrinker_alloc(0, "x86-mmu");
+	if (!mmu_shrinker)
 		goto out_shrinker;
 
+	mmu_shrinker->count_objects = mmu_shrink_count;
+	mmu_shrinker->scan_objects = mmu_shrink_scan;
+	mmu_shrinker->seeks = DEFAULT_SEEKS * 10;
+
+	shrinker_register(mmu_shrinker);
+
 	return 0;
 
 out_shrinker:
@@ -7009,7 +7011,7 @@ void kvm_mmu_vendor_module_exit(void)
 {
 	mmu_destroy_caches();
 	percpu_counter_destroy(&kvm_total_used_mmu_pages);
-	unregister_shrinker(&mmu_shrinker);
+	shrinker_unregister(mmu_shrinker);
 }
 
 /*
-- 
2.30.2

[PATCH v2 05/47] binder: dynamically allocate the android-binder shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the android-binder shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/android/binder_alloc.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index e3db8297095a..019981d65e1e 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -1053,11 +1053,7 @@ binder_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 			    NULL, sc->nr_to_scan);
 }
 
-static struct shrinker binder_shrinker = {
-	.count_objects = binder_shrink_count,
-	.scan_objects = binder_shrink_scan,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *binder_shrinker;
 
 /**
  * binder_alloc_init() - called by binder_open() for per-proc initialization
@@ -1077,19 +1073,30 @@ void binder_alloc_init(struct binder_alloc *alloc)
 
 int binder_alloc_shrinker_init(void)
 {
-	int ret = list_lru_init(&binder_alloc_lru);
+	int ret;
 
-	if (ret == 0) {
-		ret = register_shrinker(&binder_shrinker, "android-binder");
-		if (ret)
-			list_lru_destroy(&binder_alloc_lru);
+	ret = list_lru_init(&binder_alloc_lru);
+	if (ret)
+		return ret;
+
+	binder_shrinker = shrinker_alloc(0, "android-binder");
+	if (!binder_shrinker) {
+		list_lru_destroy(&binder_alloc_lru);
+		return -ENOMEM;
 	}
-	return ret;
+
+	binder_shrinker->count_objects = binder_shrink_count;
+	binder_shrinker->scan_objects = binder_shrink_scan;
+	binder_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(binder_shrinker);
+
+	return 0;
 }
 
 void binder_alloc_shrinker_exit(void)
 {
-	unregister_shrinker(&binder_shrinker);
+	shrinker_unregister(binder_shrinker);
 	list_lru_destroy(&binder_alloc_lru);
 }
 
-- 
2.30.2

[PATCH v2 06/47] drm/ttm: dynamically allocate the drm-ttm_pool shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the drm-ttm_pool shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/gpu/drm/ttm/ttm_pool.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index cddb9151d20f..e1eb73d0b72a 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -73,7 +73,7 @@ static struct ttm_pool_type global_dma32_uncached[MAX_ORDER + 1];
 
 static spinlock_t shrinker_lock;
 static struct list_head shrinker_list;
-static struct shrinker mm_shrinker;
+static struct shrinker *mm_shrinker;
 
 /* Allocate pages of size 1 << order with the given gfp_flags */
 static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags,
@@ -734,8 +734,8 @@ static int ttm_pool_debugfs_shrink_show(struct seq_file *m, void *data)
 	struct shrink_control sc = { .gfp_mask = GFP_NOFS };
 
 	fs_reclaim_acquire(GFP_KERNEL);
-	seq_printf(m, "%lu/%lu\n", ttm_pool_shrinker_count(&mm_shrinker, &sc),
-		   ttm_pool_shrinker_scan(&mm_shrinker, &sc));
+	seq_printf(m, "%lu/%lu\n", ttm_pool_shrinker_count(mm_shrinker, &sc),
+		   ttm_pool_shrinker_scan(mm_shrinker, &sc));
 	fs_reclaim_release(GFP_KERNEL);
 
 	return 0;
@@ -779,10 +779,17 @@ int ttm_pool_mgr_init(unsigned long num_pages)
 			    &ttm_pool_debugfs_shrink_fops);
 #endif
 
-	mm_shrinker.count_objects = ttm_pool_shrinker_count;
-	mm_shrinker.scan_objects = ttm_pool_shrinker_scan;
-	mm_shrinker.seeks = 1;
-	return register_shrinker(&mm_shrinker, "drm-ttm_pool");
+	mm_shrinker = shrinker_alloc(0, "drm-ttm_pool");
+	if (!mm_shrinker)
+		return -ENOMEM;
+
+	mm_shrinker->count_objects = ttm_pool_shrinker_count;
+	mm_shrinker->scan_objects = ttm_pool_shrinker_scan;
+	mm_shrinker->seeks = 1;
+
+	shrinker_register(mm_shrinker);
+
+	return 0;
 }
 
 /**
@@ -802,6 +809,6 @@ void ttm_pool_mgr_fini(void)
 		ttm_pool_type_fini(&global_dma32_uncached[i]);
 	}
 
-	unregister_shrinker(&mm_shrinker);
+	shrinker_unregister(mm_shrinker);
 	WARN_ON(!list_empty(&shrinker_list));
 }
-- 
2.30.2

[PATCH v2 07/47] xenbus/backend: dynamically allocate the xen-backend shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the xen-backend shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/xen/xenbus/xenbus_probe_backend.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index da96c260e26b..b4c3cf27af30 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -284,10 +284,7 @@ static unsigned long backend_shrink_memory_count(struct shrinker *shrinker,
 	return 0;
 }
 
-static struct shrinker backend_memory_shrinker = {
-	.count_objects = backend_shrink_memory_count,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *backend_memory_shrinker;
 
 static int __init xenbus_probe_backend_init(void)
 {
@@ -305,8 +302,16 @@ static int __init xenbus_probe_backend_init(void)
 
 	register_xenstore_notifier(&xenstore_notifier);
 
-	if (register_shrinker(&backend_memory_shrinker, "xen-backend"))
-		pr_warn("shrinker registration failed\n");
+	backend_memory_shrinker = shrinker_alloc(0, "xen-backend");
+	if (!backend_memory_shrinker) {
+		pr_warn("shrinker allocation failed\n");
+		return 0;
+	}
+
+	backend_memory_shrinker->count_objects = backend_shrink_memory_count;
+	backend_memory_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(backend_memory_shrinker);
 
 	return 0;
 }
-- 
2.30.2

[PATCH v2 08/47] erofs: dynamically allocate the erofs-shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the erofs-shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/erofs/utils.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index cc6fb9e98899..389de06e1065 100644
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -270,19 +270,25 @@ static unsigned long erofs_shrink_scan(struct shrinker *shrink,
 	return freed;
 }
 
-static struct shrinker erofs_shrinker_info = {
-	.scan_objects = erofs_shrink_scan,
-	.count_objects = erofs_shrink_count,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *erofs_shrinker_info;
 
 int __init erofs_init_shrinker(void)
 {
-	return register_shrinker(&erofs_shrinker_info, "erofs-shrinker");
+	erofs_shrinker_info = shrinker_alloc(0, "erofs-shrinker");
+	if (!erofs_shrinker_info)
+		return -ENOMEM;
+
+	erofs_shrinker_info->count_objects = erofs_shrink_count;
+	erofs_shrinker_info->scan_objects = erofs_shrink_scan;
+	erofs_shrinker_info->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(erofs_shrinker_info);
+
+	return 0;
 }
 
 void erofs_exit_shrinker(void)
 {
-	unregister_shrinker(&erofs_shrinker_info);
+	shrinker_unregister(erofs_shrinker_info);
 }
 #endif	/* !CONFIG_EROFS_FS_ZIP */
-- 
2.30.2

[PATCH v2 09/47] f2fs: dynamically allocate the f2fs-shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the f2fs-shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/f2fs/super.c | 32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index ca31163da00a..8b08473db358 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -83,11 +83,27 @@ void f2fs_build_fault_attr(struct f2fs_sb_info *sbi, unsigned int rate,
 #endif
 
 /* f2fs-wide shrinker description */
-static struct shrinker f2fs_shrinker_info = {
-	.scan_objects = f2fs_shrink_scan,
-	.count_objects = f2fs_shrink_count,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *f2fs_shrinker_info;
+
+static int f2fs_init_shrinker(void)
+{
+	f2fs_shrinker_info = shrinker_alloc(0, "f2fs-shrinker");
+	if (!f2fs_shrinker_info)
+		return -ENOMEM;
+
+	f2fs_shrinker_info->count_objects = f2fs_shrink_count;
+	f2fs_shrinker_info->scan_objects = f2fs_shrink_scan;
+	f2fs_shrinker_info->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(f2fs_shrinker_info);
+
+	return 0;
+}
+
+static void f2fs_exit_shrinker(void)
+{
+	shrinker_unregister(f2fs_shrinker_info);
+}
 
 enum {
 	Opt_gc_background,
@@ -4941,7 +4957,7 @@ static int __init init_f2fs_fs(void)
 	err = f2fs_init_sysfs();
 	if (err)
 		goto free_garbage_collection_cache;
-	err = register_shrinker(&f2fs_shrinker_info, "f2fs-shrinker");
+	err = f2fs_init_shrinker();
 	if (err)
 		goto free_sysfs;
 	err = register_filesystem(&f2fs_fs_type);
@@ -4986,7 +5002,7 @@ static int __init init_f2fs_fs(void)
 	f2fs_destroy_root_stats();
 	unregister_filesystem(&f2fs_fs_type);
 free_shrinker:
-	unregister_shrinker(&f2fs_shrinker_info);
+	f2fs_exit_shrinker();
 free_sysfs:
 	f2fs_exit_sysfs();
 free_garbage_collection_cache:
@@ -5018,7 +5034,7 @@ static void __exit exit_f2fs_fs(void)
 	f2fs_destroy_post_read_processing();
 	f2fs_destroy_root_stats();
 	unregister_filesystem(&f2fs_fs_type);
-	unregister_shrinker(&f2fs_shrinker_info);
+	f2fs_exit_shrinker();
 	f2fs_exit_sysfs();
 	f2fs_destroy_garbage_collection_cache();
 	f2fs_destroy_extent_cache();
-- 
2.30.2

[PATCH v2 10/47] gfs2: dynamically allocate the gfs2-glock shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the gfs2-glock shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/gfs2/glock.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 1438e7465e30..77da354667d9 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -2046,11 +2046,7 @@ static unsigned long gfs2_glock_shrink_count(struct shrinker *shrink,
 	return vfs_pressure_ratio(atomic_read(&lru_count));
 }
 
-static struct shrinker glock_shrinker = {
-	.seeks = DEFAULT_SEEKS,
-	.count_objects = gfs2_glock_shrink_count,
-	.scan_objects = gfs2_glock_shrink_scan,
-};
+static struct shrinker *glock_shrinker;
 
 /**
  * glock_hash_walk - Call a function for glock in a hash bucket
@@ -2472,13 +2468,19 @@ int __init gfs2_glock_init(void)
 		return -ENOMEM;
 	}
 
-	ret = register_shrinker(&glock_shrinker, "gfs2-glock");
-	if (ret) {
+	glock_shrinker = shrinker_alloc(0, "gfs2-glock");
+	if (!glock_shrinker) {
 		destroy_workqueue(glock_workqueue);
 		rhashtable_destroy(&gl_hash_table);
-		return ret;
+		return -ENOMEM;
 	}
 
+	glock_shrinker->count_objects = gfs2_glock_shrink_count;
+	glock_shrinker->scan_objects = gfs2_glock_shrink_scan;
+	glock_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(glock_shrinker);
+
 	for (i = 0; i < GLOCK_WAIT_TABLE_SIZE; i++)
 		init_waitqueue_head(glock_wait_table + i);
 
@@ -2487,7 +2489,7 @@ int __init gfs2_glock_init(void)
 
 void gfs2_glock_exit(void)
 {
-	unregister_shrinker(&glock_shrinker);
+	shrinker_unregister(glock_shrinker);
 	rhashtable_destroy(&gl_hash_table);
 	destroy_workqueue(glock_workqueue);
 }
-- 
2.30.2

[PATCH v2 11/47] gfs2: dynamically allocate the gfs2-qd shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the gfs2-qd shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/gfs2/main.c  |  6 +++---
 fs/gfs2/quota.c | 26 ++++++++++++++++++++------
 fs/gfs2/quota.h |  3 ++-
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/fs/gfs2/main.c b/fs/gfs2/main.c
index afcb32854f14..e47b1cc79f59 100644
--- a/fs/gfs2/main.c
+++ b/fs/gfs2/main.c
@@ -147,7 +147,7 @@ static int __init init_gfs2_fs(void)
 	if (!gfs2_trans_cachep)
 		goto fail_cachep8;
 
-	error = register_shrinker(&gfs2_qd_shrinker, "gfs2-qd");
+	error = gfs2_qd_shrinker_init();
 	if (error)
 		goto fail_shrinker;
 
@@ -196,7 +196,7 @@ static int __init init_gfs2_fs(void)
 fail_wq2:
 	destroy_workqueue(gfs_recovery_wq);
 fail_wq1:
-	unregister_shrinker(&gfs2_qd_shrinker);
+	gfs2_qd_shrinker_exit();
 fail_shrinker:
 	kmem_cache_destroy(gfs2_trans_cachep);
 fail_cachep8:
@@ -229,7 +229,7 @@ static int __init init_gfs2_fs(void)
 
 static void __exit exit_gfs2_fs(void)
 {
-	unregister_shrinker(&gfs2_qd_shrinker);
+	gfs2_qd_shrinker_exit();
 	gfs2_glock_exit();
 	gfs2_unregister_debugfs();
 	unregister_filesystem(&gfs2_fs_type);
diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
index 704192b73605..bc9883cea847 100644
--- a/fs/gfs2/quota.c
+++ b/fs/gfs2/quota.c
@@ -186,13 +186,27 @@ static unsigned long gfs2_qd_shrink_count(struct shrinker *shrink,
 	return vfs_pressure_ratio(list_lru_shrink_count(&gfs2_qd_lru, sc));
 }
 
-struct shrinker gfs2_qd_shrinker = {
-	.count_objects = gfs2_qd_shrink_count,
-	.scan_objects = gfs2_qd_shrink_scan,
-	.seeks = DEFAULT_SEEKS,
-	.flags = SHRINKER_NUMA_AWARE,
-};
+static struct shrinker *gfs2_qd_shrinker;
+
+int gfs2_qd_shrinker_init(void)
+{
+	gfs2_qd_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE, "gfs2-qd");
+	if (!gfs2_qd_shrinker)
+		return -ENOMEM;
+
+	gfs2_qd_shrinker->count_objects = gfs2_qd_shrink_count;
+	gfs2_qd_shrinker->scan_objects = gfs2_qd_shrink_scan;
+	gfs2_qd_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(gfs2_qd_shrinker);
 
+	return 0;
+}
+
+void gfs2_qd_shrinker_exit(void)
+{
+	shrinker_unregister(gfs2_qd_shrinker);
+}
 
 static u64 qd2index(struct gfs2_quota_data *qd)
 {
diff --git a/fs/gfs2/quota.h b/fs/gfs2/quota.h
index 21ada332d555..f9cb863373f7 100644
--- a/fs/gfs2/quota.h
+++ b/fs/gfs2/quota.h
@@ -59,7 +59,8 @@ static inline int gfs2_quota_lock_check(struct gfs2_inode *ip,
 }
 
 extern const struct quotactl_ops gfs2_quotactl_ops;
-extern struct shrinker gfs2_qd_shrinker;
+int gfs2_qd_shrinker_init(void);
+void gfs2_qd_shrinker_exit(void);
 extern struct list_lru gfs2_qd_lru;
 extern void __init gfs2_quota_hash_init(void);
 
-- 
2.30.2

[PATCH v2 12/47] NFSv4.2: dynamically allocate the nfs-xattr shrinkers

[Qi Zheng]

Use new APIs to dynamically allocate the nfs-xattr shrinkers.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/nfs/nfs42xattr.c | 87 +++++++++++++++++++++++----------------------
 1 file changed, 44 insertions(+), 43 deletions(-)

diff --git a/fs/nfs/nfs42xattr.c b/fs/nfs/nfs42xattr.c
index 911f634ba3da..3604342e0f77 100644
--- a/fs/nfs/nfs42xattr.c
+++ b/fs/nfs/nfs42xattr.c
@@ -796,28 +796,9 @@ static unsigned long nfs4_xattr_cache_scan(struct shrinker *shrink,
 static unsigned long nfs4_xattr_entry_scan(struct shrinker *shrink,
 					   struct shrink_control *sc);
 
-static struct shrinker nfs4_xattr_cache_shrinker = {
-	.count_objects	= nfs4_xattr_cache_count,
-	.scan_objects	= nfs4_xattr_cache_scan,
-	.seeks		= DEFAULT_SEEKS,
-	.flags		= SHRINKER_MEMCG_AWARE,
-};
-
-static struct shrinker nfs4_xattr_entry_shrinker = {
-	.count_objects	= nfs4_xattr_entry_count,
-	.scan_objects	= nfs4_xattr_entry_scan,
-	.seeks		= DEFAULT_SEEKS,
-	.batch		= 512,
-	.flags		= SHRINKER_MEMCG_AWARE,
-};
-
-static struct shrinker nfs4_xattr_large_entry_shrinker = {
-	.count_objects	= nfs4_xattr_entry_count,
-	.scan_objects	= nfs4_xattr_entry_scan,
-	.seeks		= 1,
-	.batch		= 512,
-	.flags		= SHRINKER_MEMCG_AWARE,
-};
+static struct shrinker *nfs4_xattr_cache_shrinker;
+static struct shrinker *nfs4_xattr_entry_shrinker;
+static struct shrinker *nfs4_xattr_large_entry_shrinker;
 
 static enum lru_status
 cache_lru_isolate(struct list_head *item,
@@ -943,7 +924,7 @@ nfs4_xattr_entry_scan(struct shrinker *shrink, struct shrink_control *sc)
 	struct nfs4_xattr_entry *entry;
 	struct list_lru *lru;
 
-	lru = (shrink == &nfs4_xattr_large_entry_shrinker) ?
+	lru = (shrink == nfs4_xattr_large_entry_shrinker) ?
 	    &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;
 
 	freed = list_lru_shrink_walk(lru, sc, entry_lru_isolate, &dispose);
@@ -971,7 +952,7 @@ nfs4_xattr_entry_count(struct shrinker *shrink, struct shrink_control *sc)
 	unsigned long count;
 	struct list_lru *lru;
 
-	lru = (shrink == &nfs4_xattr_large_entry_shrinker) ?
+	lru = (shrink == nfs4_xattr_large_entry_shrinker) ?
 	    &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;
 
 	count = list_lru_shrink_count(lru, sc);
@@ -991,18 +972,34 @@ static void nfs4_xattr_cache_init_once(void *p)
 	INIT_LIST_HEAD(&cache->dispose);
 }
 
-static int nfs4_xattr_shrinker_init(struct shrinker *shrinker,
-				    struct list_lru *lru, const char *name)
+typedef unsigned long (*count_objects_cb)(struct shrinker *s,
+					  struct shrink_control *sc);
+typedef unsigned long (*scan_objects_cb)(struct shrinker *s,
+					 struct shrink_control *sc);
+
+static int nfs4_xattr_shrinker_init(struct shrinker **shrinker,
+				    struct list_lru *lru, const char *name,
+				    count_objects_cb count,
+				    scan_objects_cb scan, long batch, int seeks)
 {
-	int ret = 0;
+	int ret;
 
-	ret = register_shrinker(shrinker, name);
-	if (ret)
+	*shrinker = shrinker_alloc(SHRINKER_MEMCG_AWARE, name);
+	if (!*shrinker)
+		return -ENOMEM;
+
+	ret = list_lru_init_memcg(lru, *shrinker);
+	if (ret) {
+		shrinker_free_non_registered(*shrinker);
 		return ret;
+	}
 
-	ret = list_lru_init_memcg(lru, shrinker);
-	if (ret)
-		unregister_shrinker(shrinker);
+	(*shrinker)->count_objects = count;
+	(*shrinker)->scan_objects = scan;
+	(*shrinker)->batch = batch;
+	(*shrinker)->seeks = seeks;
+
+	shrinker_register(*shrinker);
 
 	return ret;
 }
@@ -1010,7 +1007,7 @@ static int nfs4_xattr_shrinker_init(struct shrinker *shrinker,
 static void nfs4_xattr_shrinker_destroy(struct shrinker *shrinker,
 					struct list_lru *lru)
 {
-	unregister_shrinker(shrinker);
+	shrinker_unregister(shrinker);
 	list_lru_destroy(lru);
 }
 
@@ -1026,27 +1023,31 @@ int __init nfs4_xattr_cache_init(void)
 		return -ENOMEM;
 
 	ret = nfs4_xattr_shrinker_init(&nfs4_xattr_cache_shrinker,
-				       &nfs4_xattr_cache_lru,
-				       "nfs-xattr_cache");
+				       &nfs4_xattr_cache_lru, "nfs-xattr_cache",
+				       nfs4_xattr_cache_count,
+				       nfs4_xattr_cache_scan, 0, DEFAULT_SEEKS);
 	if (ret)
 		goto out1;
 
 	ret = nfs4_xattr_shrinker_init(&nfs4_xattr_entry_shrinker,
-				       &nfs4_xattr_entry_lru,
-				       "nfs-xattr_entry");
+				       &nfs4_xattr_entry_lru, "nfs-xattr_entry",
+				       nfs4_xattr_entry_count,
+				       nfs4_xattr_entry_scan, 512, DEFAULT_SEEKS);
 	if (ret)
 		goto out2;
 
 	ret = nfs4_xattr_shrinker_init(&nfs4_xattr_large_entry_shrinker,
 				       &nfs4_xattr_large_entry_lru,
-				       "nfs-xattr_large_entry");
+				       "nfs-xattr_large_entry",
+				       nfs4_xattr_entry_count,
+				       nfs4_xattr_entry_scan, 512, 1);
 	if (!ret)
 		return 0;
 
-	nfs4_xattr_shrinker_destroy(&nfs4_xattr_entry_shrinker,
+	nfs4_xattr_shrinker_destroy(nfs4_xattr_entry_shrinker,
 				    &nfs4_xattr_entry_lru);
 out2:
-	nfs4_xattr_shrinker_destroy(&nfs4_xattr_cache_shrinker,
+	nfs4_xattr_shrinker_destroy(nfs4_xattr_cache_shrinker,
 				    &nfs4_xattr_cache_lru);
 out1:
 	kmem_cache_destroy(nfs4_xattr_cache_cachep);
@@ -1056,11 +1057,11 @@ int __init nfs4_xattr_cache_init(void)
 
 void nfs4_xattr_cache_exit(void)
 {
-	nfs4_xattr_shrinker_destroy(&nfs4_xattr_large_entry_shrinker,
+	nfs4_xattr_shrinker_destroy(nfs4_xattr_large_entry_shrinker,
 				    &nfs4_xattr_large_entry_lru);
-	nfs4_xattr_shrinker_destroy(&nfs4_xattr_entry_shrinker,
+	nfs4_xattr_shrinker_destroy(nfs4_xattr_entry_shrinker,
 				    &nfs4_xattr_entry_lru);
-	nfs4_xattr_shrinker_destroy(&nfs4_xattr_cache_shrinker,
+	nfs4_xattr_shrinker_destroy(nfs4_xattr_cache_shrinker,
 				    &nfs4_xattr_cache_lru);
 	kmem_cache_destroy(nfs4_xattr_cache_cachep);
 }
-- 
2.30.2

[PATCH v2 13/47] nfs: dynamically allocate the nfs-acl shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the nfs-acl shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/nfs/super.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 2284f749d892..a90b12593383 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -129,11 +129,7 @@ static void nfs_ssc_unregister_ops(void)
 }
 #endif /* CONFIG_NFS_V4_2 */
 
-static struct shrinker acl_shrinker = {
-	.count_objects	= nfs_access_cache_count,
-	.scan_objects	= nfs_access_cache_scan,
-	.seeks		= DEFAULT_SEEKS,
-};
+static struct shrinker *acl_shrinker;
 
 /*
  * Register the NFS filesystems
@@ -153,9 +149,17 @@ int __init register_nfs_fs(void)
 	ret = nfs_register_sysctl();
 	if (ret < 0)
 		goto error_2;
-	ret = register_shrinker(&acl_shrinker, "nfs-acl");
-	if (ret < 0)
+
+	acl_shrinker = shrinker_alloc(0, "nfs-acl");
+	if (!acl_shrinker)
 		goto error_3;
+
+	acl_shrinker->count_objects = nfs_access_cache_count;
+	acl_shrinker->scan_objects = nfs_access_cache_scan;
+	acl_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(acl_shrinker);
+
 #ifdef CONFIG_NFS_V4_2
 	nfs_ssc_register_ops();
 #endif
@@ -175,7 +179,7 @@ int __init register_nfs_fs(void)
  */
 void __exit unregister_nfs_fs(void)
 {
-	unregister_shrinker(&acl_shrinker);
+	shrinker_unregister(acl_shrinker);
 	nfs_unregister_sysctl();
 	unregister_nfs4_fs();
 #ifdef CONFIG_NFS_V4_2
-- 
2.30.2

[PATCH v2 14/47] nfsd: dynamically allocate the nfsd-filecache shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the nfsd-filecache shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/nfsd/filecache.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index ee9c923192e0..50216768d408 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -521,11 +521,7 @@ nfsd_file_lru_scan(struct shrinker *s, struct shrink_control *sc)
 	return ret;
 }
 
-static struct shrinker	nfsd_file_shrinker = {
-	.scan_objects = nfsd_file_lru_scan,
-	.count_objects = nfsd_file_lru_count,
-	.seeks = 1,
-};
+static struct shrinker *nfsd_file_shrinker;
 
 /**
  * nfsd_file_cond_queue - conditionally unhash and queue a nfsd_file
@@ -746,12 +742,18 @@ nfsd_file_cache_init(void)
 		goto out_err;
 	}
 
-	ret = register_shrinker(&nfsd_file_shrinker, "nfsd-filecache");
-	if (ret) {
-		pr_err("nfsd: failed to register nfsd_file_shrinker: %d\n", ret);
+	nfsd_file_shrinker = shrinker_alloc(0, "nfsd-filecache");
+	if (!nfsd_file_shrinker) {
+		pr_err("nfsd: failed to allocate nfsd_file_shrinker\n");
 		goto out_lru;
 	}
 
+	nfsd_file_shrinker->count_objects = nfsd_file_lru_count;
+	nfsd_file_shrinker->scan_objects = nfsd_file_lru_scan;
+	nfsd_file_shrinker->seeks = 1;
+
+	shrinker_register(nfsd_file_shrinker);
+
 	ret = lease_register_notifier(&nfsd_file_lease_notifier);
 	if (ret) {
 		pr_err("nfsd: unable to register lease notifier: %d\n", ret);
@@ -774,7 +776,7 @@ nfsd_file_cache_init(void)
 out_notifier:
 	lease_unregister_notifier(&nfsd_file_lease_notifier);
 out_shrinker:
-	unregister_shrinker(&nfsd_file_shrinker);
+	shrinker_unregister(nfsd_file_shrinker);
 out_lru:
 	list_lru_destroy(&nfsd_file_lru);
 out_err:
@@ -891,7 +893,7 @@ nfsd_file_cache_shutdown(void)
 		return;
 
 	lease_unregister_notifier(&nfsd_file_lease_notifier);
-	unregister_shrinker(&nfsd_file_shrinker);
+	shrinker_unregister(nfsd_file_shrinker);
 	/*
 	 * make sure all callers of nfsd_file_lru_cb are done before
 	 * calling nfsd_file_cache_purge
-- 
2.30.2

[PATCH v2 15/47] quota: dynamically allocate the dquota-cache shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the dquota-cache shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/quota/dquot.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index e8232242dd34..6cb2d8911bc3 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -791,11 +791,7 @@ dqcache_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 	percpu_counter_read_positive(&dqstats.counter[DQST_FREE_DQUOTS]));
 }
 
-static struct shrinker dqcache_shrinker = {
-	.count_objects = dqcache_shrink_count,
-	.scan_objects = dqcache_shrink_scan,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *dqcache_shrinker;
 
 /*
  * Safely release dquot and put reference to dquot.
@@ -2991,8 +2987,15 @@ static int __init dquot_init(void)
 	pr_info("VFS: Dquot-cache hash table entries: %ld (order %ld,"
 		" %ld bytes)\n", nr_hash, order, (PAGE_SIZE << order));
 
-	if (register_shrinker(&dqcache_shrinker, "dquota-cache"))
-		panic("Cannot register dquot shrinker");
+	dqcache_shrinker = shrinker_alloc(0, "dquota-cache");
+	if (!dqcache_shrinker)
+		panic("Cannot allocate dquot shrinker");
+
+	dqcache_shrinker->count_objects = dqcache_shrink_count;
+	dqcache_shrinker->scan_objects = dqcache_shrink_scan;
+	dqcache_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(dqcache_shrinker);
 
 	return 0;
 }
-- 
2.30.2

[PATCH v2 16/47] ubifs: dynamically allocate the ubifs-slab shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the ubifs-slab shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/ubifs/super.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 32cb14759796..f2a3a58f7860 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -54,11 +54,7 @@ module_param_cb(default_version, &ubifs_default_version_ops, &ubifs_default_vers
 static struct kmem_cache *ubifs_inode_slab;
 
 /* UBIFS TNC shrinker description */
-static struct shrinker ubifs_shrinker_info = {
-	.scan_objects = ubifs_shrink_scan,
-	.count_objects = ubifs_shrink_count,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *ubifs_shrinker_info;
 
 /**
  * validate_inode - validate inode.
@@ -2373,7 +2369,7 @@ static void inode_slab_ctor(void *obj)
 
 static int __init ubifs_init(void)
 {
-	int err;
+	int err = -ENOMEM;
 
 	BUILD_BUG_ON(sizeof(struct ubifs_ch) != 24);
 
@@ -2439,10 +2435,16 @@ static int __init ubifs_init(void)
 	if (!ubifs_inode_slab)
 		return -ENOMEM;
 
-	err = register_shrinker(&ubifs_shrinker_info, "ubifs-slab");
-	if (err)
+	ubifs_shrinker_info = shrinker_alloc(0, "ubifs-slab");
+	if (!ubifs_shrinker_info)
 		goto out_slab;
 
+	ubifs_shrinker_info->count_objects = ubifs_shrink_count;
+	ubifs_shrinker_info->scan_objects = ubifs_shrink_scan;
+	ubifs_shrinker_info->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(ubifs_shrinker_info);
+
 	err = ubifs_compressors_init();
 	if (err)
 		goto out_shrinker;
@@ -2467,7 +2469,7 @@ static int __init ubifs_init(void)
 	dbg_debugfs_exit();
 	ubifs_compressors_exit();
 out_shrinker:
-	unregister_shrinker(&ubifs_shrinker_info);
+	shrinker_unregister(ubifs_shrinker_info);
 out_slab:
 	kmem_cache_destroy(ubifs_inode_slab);
 	return err;
@@ -2483,7 +2485,7 @@ static void __exit ubifs_exit(void)
 	dbg_debugfs_exit();
 	ubifs_sysfs_exit();
 	ubifs_compressors_exit();
-	unregister_shrinker(&ubifs_shrinker_info);
+	shrinker_unregister(ubifs_shrinker_info);
 
 	/*
 	 * Make sure all delayed rcu free inodes are flushed before we
-- 
2.30.2

[PATCH v2 17/47] rcu: dynamically allocate the rcu-lazy shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the rcu-lazy shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 kernel/rcu/tree_nocb.h | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 43229d2b0c44..919f17561733 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1397,12 +1397,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 	return count ? count : SHRINK_STOP;
 }
 
-static struct shrinker lazy_rcu_shrinker = {
-	.count_objects = lazy_rcu_shrink_count,
-	.scan_objects = lazy_rcu_shrink_scan,
-	.batch = 0,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *lazy_rcu_shrinker;
 #endif // #ifdef CONFIG_RCU_LAZY
 
 void __init rcu_init_nohz(void)
@@ -1436,8 +1431,16 @@ void __init rcu_init_nohz(void)
 		return;
 
 #ifdef CONFIG_RCU_LAZY
-	if (register_shrinker(&lazy_rcu_shrinker, "rcu-lazy"))
-		pr_err("Failed to register lazy_rcu shrinker!\n");
+	lazy_rcu_shrinker = shrinker_alloc(0, "rcu-lazy");
+	if (!lazy_rcu_shrinker) {
+		pr_err("Failed to allocate lazy_rcu shrinker!\n");
+	} else {
+		lazy_rcu_shrinker->count_objects = lazy_rcu_shrink_count;
+		lazy_rcu_shrinker->scan_objects = lazy_rcu_shrink_scan;
+		lazy_rcu_shrinker->seeks = DEFAULT_SEEKS;
+
+		shrinker_register(lazy_rcu_shrinker);
+	}
 #endif // #ifdef CONFIG_RCU_LAZY
 
 	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
-- 
2.30.2

[PATCH v2 18/47] rcu: dynamically allocate the rcu-kfree shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the rcu-kfree shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 kernel/rcu/tree.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1449cb69a0e0..d068ce3567fc 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3445,12 +3445,7 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 	return freed == 0 ? SHRINK_STOP : freed;
 }
 
-static struct shrinker kfree_rcu_shrinker = {
-	.count_objects = kfree_rcu_shrink_count,
-	.scan_objects = kfree_rcu_shrink_scan,
-	.batch = 0,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *kfree_rcu_shrinker;
 
 void __init kfree_rcu_scheduler_running(void)
 {
@@ -4958,8 +4953,18 @@ static void __init kfree_rcu_batch_init(void)
 		INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
 		krcp->initialized = true;
 	}
-	if (register_shrinker(&kfree_rcu_shrinker, "rcu-kfree"))
-		pr_err("Failed to register kfree_rcu() shrinker!\n");
+
+	kfree_rcu_shrinker = shrinker_alloc(0, "rcu-kfree");
+	if (!kfree_rcu_shrinker) {
+		pr_err("Failed to allocate kfree_rcu() shrinker!\n");
+		return;
+	}
+
+	kfree_rcu_shrinker->count_objects = kfree_rcu_shrink_count;
+	kfree_rcu_shrinker->scan_objects = kfree_rcu_shrink_scan;
+	kfree_rcu_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(kfree_rcu_shrinker);
 }
 
 void __init rcu_init(void)
-- 
2.30.2

[PATCH v2 19/47] mm: thp: dynamically allocate the thp-related shrinkers

[Qi Zheng]

Use new APIs to dynamically allocate the thp-zero and thp-deferred_split
shrinkers.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/huge_memory.c | 69 +++++++++++++++++++++++++++++++-----------------
 1 file changed, 45 insertions(+), 24 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8c94b34024a2..4db5a1834d81 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -65,7 +65,11 @@ unsigned long transparent_hugepage_flags __read_mostly =
 	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
 	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 
-static struct shrinker deferred_split_shrinker;
+static struct shrinker *deferred_split_shrinker;
+static unsigned long deferred_split_count(struct shrinker *shrink,
+					  struct shrink_control *sc);
+static unsigned long deferred_split_scan(struct shrinker *shrink,
+					 struct shrink_control *sc);
 
 static atomic_t huge_zero_refcount;
 struct page *huge_zero_page __read_mostly;
@@ -229,11 +233,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 	return 0;
 }
 
-static struct shrinker huge_zero_page_shrinker = {
-	.count_objects = shrink_huge_zero_page_count,
-	.scan_objects = shrink_huge_zero_page_scan,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *huge_zero_page_shrinker;
 
 #ifdef CONFIG_SYSFS
 static ssize_t enabled_show(struct kobject *kobj,
@@ -454,6 +454,40 @@ static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 }
 #endif /* CONFIG_SYSFS */
 
+static int thp_shrinker_init(void)
+{
+	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
+	if (!huge_zero_page_shrinker)
+		return -ENOMEM;
+
+	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
+						 SHRINKER_MEMCG_AWARE |
+						 SHRINKER_NONSLAB,
+						 "thp-deferred_split");
+	if (!deferred_split_shrinker) {
+		shrinker_free_non_registered(huge_zero_page_shrinker);
+		return -ENOMEM;
+	}
+
+	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
+	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
+	huge_zero_page_shrinker->seeks = DEFAULT_SEEKS;
+	shrinker_register(huge_zero_page_shrinker);
+
+	deferred_split_shrinker->count_objects = deferred_split_count;
+	deferred_split_shrinker->scan_objects = deferred_split_scan;
+	deferred_split_shrinker->seeks = DEFAULT_SEEKS;
+	shrinker_register(deferred_split_shrinker);
+
+	return 0;
+}
+
+static void thp_shrinker_exit(void)
+{
+	shrinker_unregister(huge_zero_page_shrinker);
+	shrinker_unregister(deferred_split_shrinker);
+}
+
 static int __init hugepage_init(void)
 {
 	int err;
@@ -482,12 +516,9 @@ static int __init hugepage_init(void)
 	if (err)
 		goto err_slab;
 
-	err = register_shrinker(&huge_zero_page_shrinker, "thp-zero");
-	if (err)
-		goto err_hzp_shrinker;
-	err = register_shrinker(&deferred_split_shrinker, "thp-deferred_split");
+	err = thp_shrinker_init();
 	if (err)
-		goto err_split_shrinker;
+		goto err_shrinker;
 
 	/*
 	 * By default disable transparent hugepages on smaller systems,
@@ -505,10 +536,8 @@ static int __init hugepage_init(void)
 
 	return 0;
 err_khugepaged:
-	unregister_shrinker(&deferred_split_shrinker);
-err_split_shrinker:
-	unregister_shrinker(&huge_zero_page_shrinker);
-err_hzp_shrinker:
+	thp_shrinker_exit();
+err_shrinker:
 	khugepaged_destroy();
 err_slab:
 	hugepage_exit_sysfs(hugepage_kobj);
@@ -2851,7 +2880,7 @@ void deferred_split_folio(struct folio *folio)
 #ifdef CONFIG_MEMCG
 		if (memcg)
 			set_shrinker_bit(memcg, folio_nid(folio),
-					 deferred_split_shrinker.id);
+					 deferred_split_shrinker->id);
 #endif
 	}
 	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
@@ -2925,14 +2954,6 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 	return split;
 }
 
-static struct shrinker deferred_split_shrinker = {
-	.count_objects = deferred_split_count,
-	.scan_objects = deferred_split_scan,
-	.seeks = DEFAULT_SEEKS,
-	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE |
-		 SHRINKER_NONSLAB,
-};
-
 #ifdef CONFIG_DEBUG_FS
 static void split_huge_pages_all(void)
 {
-- 
2.30.2

[PATCH v2 20/47] sunrpc: dynamically allocate the sunrpc_cred shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the sunrpc_cred shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 net/sunrpc/auth.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
index 2f16f9d17966..74e40c8a512d 100644
--- a/net/sunrpc/auth.c
+++ b/net/sunrpc/auth.c
@@ -861,11 +861,7 @@ rpcauth_uptodatecred(struct rpc_task *task)
 		test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) != 0;
 }
 
-static struct shrinker rpc_cred_shrinker = {
-	.count_objects = rpcauth_cache_shrink_count,
-	.scan_objects = rpcauth_cache_shrink_scan,
-	.seeks = DEFAULT_SEEKS,
-};
+static struct shrinker *rpc_cred_shrinker;
 
 int __init rpcauth_init_module(void)
 {
@@ -874,9 +870,16 @@ int __init rpcauth_init_module(void)
 	err = rpc_init_authunix();
 	if (err < 0)
 		goto out1;
-	err = register_shrinker(&rpc_cred_shrinker, "sunrpc_cred");
-	if (err < 0)
+	rpc_cred_shrinker = shrinker_alloc(0, "sunrpc_cred");
+	if (!rpc_cred_shrinker)
 		goto out2;
+
+	rpc_cred_shrinker->count_objects = rpcauth_cache_shrink_count;
+	rpc_cred_shrinker->scan_objects = rpcauth_cache_shrink_scan;
+	rpc_cred_shrinker->seeks = DEFAULT_SEEKS;
+
+	shrinker_register(rpc_cred_shrinker);
+
 	return 0;
 out2:
 	rpc_destroy_authunix();
@@ -887,5 +890,5 @@ int __init rpcauth_init_module(void)
 void rpcauth_remove_module(void)
 {
 	rpc_destroy_authunix();
-	unregister_shrinker(&rpc_cred_shrinker);
+	shrinker_unregister(rpc_cred_shrinker);
 }
-- 
2.30.2

[PATCH v2 21/47] mm: workingset: dynamically allocate the mm-shadow shrinker

[Qi Zheng]

Use new APIs to dynamically allocate the mm-shadow shrinker.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/workingset.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/mm/workingset.c b/mm/workingset.c
index 4686ae363000..4bc85f739b13 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -762,12 +762,7 @@ static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
 					NULL);
 }
 
-static struct shrinker workingset_shadow_shrinker = {
-	.count_objects = count_shadow_nodes,
-	.scan_objects = scan_shadow_nodes,
-	.seeks = 0, /* ->count reports only fully expendable nodes */
-	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
-};
+static struct shrinker *workingset_shadow_shrinker;
 
 /*
  * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
@@ -779,7 +774,7 @@ static int __init workingset_init(void)
 {
 	unsigned int timestamp_bits;
 	unsigned int max_order;
-	int ret;
+	int ret = -ENOMEM;
 
 	BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
 	/*
@@ -796,17 +791,24 @@ static int __init workingset_init(void)
 	pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
 	       timestamp_bits, max_order, bucket_order);
 
-	ret = prealloc_shrinker(&workingset_shadow_shrinker, "mm-shadow");
-	if (ret)
+	workingset_shadow_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
+						    SHRINKER_MEMCG_AWARE,
+						    "mm-shadow");
+	if (!workingset_shadow_shrinker)
 		goto err;
+
 	ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
-			      &workingset_shadow_shrinker);
+			      workingset_shadow_shrinker);
 	if (ret)
 		goto err_list_lru;
-	register_shrinker_prepared(&workingset_shadow_shrinker);
+
+	workingset_shadow_shrinker->count_objects = count_shadow_nodes;
+	workingset_shadow_shrinker->scan_objects = scan_shadow_nodes;
+
+	shrinker_register(workingset_shadow_shrinker);
 	return 0;
 err_list_lru:
-	free_prealloced_shrinker(&workingset_shadow_shrinker);
+	shrinker_free_non_registered(workingset_shadow_shrinker);
 err:
 	return ret;
 }
-- 
2.30.2

[PATCH v2 22/47] drm/i915: dynamically allocate the i915_gem_mm shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the i915_gem_mm shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct drm_i915_private.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 30 +++++++++++---------
 drivers/gpu/drm/i915/i915_drv.h              |  2 +-
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
index 214763942aa2..a7409b8c2634 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
@@ -284,8 +284,7 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *i915)
 static unsigned long
 i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 {
-	struct drm_i915_private *i915 =
-		container_of(shrinker, struct drm_i915_private, mm.shrinker);
+	struct drm_i915_private *i915 = shrinker->private_data;
 	unsigned long num_objects;
 	unsigned long count;
 
@@ -302,8 +301,8 @@ i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 	if (num_objects) {
 		unsigned long avg = 2 * count / num_objects;
 
-		i915->mm.shrinker.batch =
-			max((i915->mm.shrinker.batch + avg) >> 1,
+		i915->mm.shrinker->batch =
+			max((i915->mm.shrinker->batch + avg) >> 1,
 			    128ul /* default SHRINK_BATCH */);
 	}
 
@@ -313,8 +312,7 @@ i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 static unsigned long
 i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 {
-	struct drm_i915_private *i915 =
-		container_of(shrinker, struct drm_i915_private, mm.shrinker);
+	struct drm_i915_private *i915 = shrinker->private_data;
 	unsigned long freed;
 
 	sc->nr_scanned = 0;
@@ -422,12 +420,18 @@ i915_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr
 
 void i915_gem_driver_register__shrinker(struct drm_i915_private *i915)
 {
-	i915->mm.shrinker.scan_objects = i915_gem_shrinker_scan;
-	i915->mm.shrinker.count_objects = i915_gem_shrinker_count;
-	i915->mm.shrinker.seeks = DEFAULT_SEEKS;
-	i915->mm.shrinker.batch = 4096;
-	drm_WARN_ON(&i915->drm, register_shrinker(&i915->mm.shrinker,
-						  "drm-i915_gem"));
+	i915->mm.shrinker = shrinker_alloc(0, "drm-i915_gem");
+	if (!i915->mm.shrinker) {
+		drm_WARN_ON(&i915->drm, 1);
+	} else {
+		i915->mm.shrinker->scan_objects = i915_gem_shrinker_scan;
+		i915->mm.shrinker->count_objects = i915_gem_shrinker_count;
+		i915->mm.shrinker->seeks = DEFAULT_SEEKS;
+		i915->mm.shrinker->batch = 4096;
+		i915->mm.shrinker->private_data = i915;
+
+		shrinker_register(i915->mm.shrinker);
+	}
 
 	i915->mm.oom_notifier.notifier_call = i915_gem_shrinker_oom;
 	drm_WARN_ON(&i915->drm, register_oom_notifier(&i915->mm.oom_notifier));
@@ -443,7 +447,7 @@ void i915_gem_driver_unregister__shrinker(struct drm_i915_private *i915)
 		    unregister_vmap_purge_notifier(&i915->mm.vmap_notifier));
 	drm_WARN_ON(&i915->drm,
 		    unregister_oom_notifier(&i915->mm.oom_notifier));
-	unregister_shrinker(&i915->mm.shrinker);
+	shrinker_unregister(i915->mm.shrinker);
 }
 
 void i915_gem_shrinker_taints_mutex(struct drm_i915_private *i915,
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 682ef2b5c7d5..389e8bf140d7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -163,7 +163,7 @@ struct i915_gem_mm {
 
 	struct notifier_block oom_notifier;
 	struct notifier_block vmap_notifier;
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 
 #ifdef CONFIG_MMU_NOTIFIER
 	/**
-- 
2.30.2

[PATCH v2 23/47] drm/msm: dynamically allocate the drm-msm_gem shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the drm-msm_gem shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct msm_drm_private.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/gpu/drm/msm/msm_drv.c          |  4 ++-
 drivers/gpu/drm/msm/msm_drv.h          |  4 +--
 drivers/gpu/drm/msm/msm_gem_shrinker.c | 36 ++++++++++++++++----------
 3 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 891eff8433a9..7f6933be703f 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -461,7 +461,9 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)
 	if (ret)
 		goto err_msm_uninit;
 
-	msm_gem_shrinker_init(ddev);
+	ret = msm_gem_shrinker_init(ddev);
+	if (ret)
+		goto err_msm_uninit;
 
 	if (priv->kms_init) {
 		ret = priv->kms_init(ddev);
diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index e13a8cbd61c9..84523d4a1e58 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -217,7 +217,7 @@ struct msm_drm_private {
 	} vram;
 
 	struct notifier_block vmap_notifier;
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 
 	struct drm_atomic_state *pm_state;
 
@@ -279,7 +279,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 unsigned long msm_gem_shrinker_shrink(struct drm_device *dev, unsigned long nr_to_scan);
 #endif
 
-void msm_gem_shrinker_init(struct drm_device *dev);
+int msm_gem_shrinker_init(struct drm_device *dev);
 void msm_gem_shrinker_cleanup(struct drm_device *dev);
 
 int msm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
index f38296ad8743..7daab1298c11 100644
--- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
+++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
@@ -34,8 +34,7 @@ static bool can_block(struct shrink_control *sc)
 static unsigned long
 msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 {
-	struct msm_drm_private *priv =
-		container_of(shrinker, struct msm_drm_private, shrinker);
+	struct msm_drm_private *priv = shrinker->private_data;
 	unsigned count = priv->lru.dontneed.count;
 
 	if (can_swap())
@@ -100,8 +99,7 @@ active_evict(struct drm_gem_object *obj)
 static unsigned long
 msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 {
-	struct msm_drm_private *priv =
-		container_of(shrinker, struct msm_drm_private, shrinker);
+	struct msm_drm_private *priv = shrinker->private_data;
 	struct {
 		struct drm_gem_lru *lru;
 		bool (*shrink)(struct drm_gem_object *obj);
@@ -148,10 +146,11 @@ msm_gem_shrinker_shrink(struct drm_device *dev, unsigned long nr_to_scan)
 	struct shrink_control sc = {
 		.nr_to_scan = nr_to_scan,
 	};
-	int ret;
+	unsigned long ret = SHRINK_STOP;
 
 	fs_reclaim_acquire(GFP_KERNEL);
-	ret = msm_gem_shrinker_scan(&priv->shrinker, &sc);
+	if (priv->shrinker)
+		ret = msm_gem_shrinker_scan(priv->shrinker, &sc);
 	fs_reclaim_release(GFP_KERNEL);
 
 	return ret;
@@ -210,16 +209,27 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
  *
  * This function registers and sets up the msm shrinker.
  */
-void msm_gem_shrinker_init(struct drm_device *dev)
+int msm_gem_shrinker_init(struct drm_device *dev)
 {
 	struct msm_drm_private *priv = dev->dev_private;
-	priv->shrinker.count_objects = msm_gem_shrinker_count;
-	priv->shrinker.scan_objects = msm_gem_shrinker_scan;
-	priv->shrinker.seeks = DEFAULT_SEEKS;
-	WARN_ON(register_shrinker(&priv->shrinker, "drm-msm_gem"));
+
+	priv->shrinker = shrinker_alloc(0, "drm-msm_gem");
+	if (!priv->shrinker) {
+		WARN_ON(1);
+		return -ENOMEM;
+	}
+
+	priv->shrinker->count_objects = msm_gem_shrinker_count;
+	priv->shrinker->scan_objects = msm_gem_shrinker_scan;
+	priv->shrinker->seeks = DEFAULT_SEEKS;
+	priv->shrinker->private_data = priv;
+
+	shrinker_register(priv->shrinker);
 
 	priv->vmap_notifier.notifier_call = msm_gem_shrinker_vmap;
 	WARN_ON(register_vmap_purge_notifier(&priv->vmap_notifier));
+
+	return 0;
 }
 
 /**
@@ -232,8 +242,8 @@ void msm_gem_shrinker_cleanup(struct drm_device *dev)
 {
 	struct msm_drm_private *priv = dev->dev_private;
 
-	if (priv->shrinker.nr_deferred) {
+	if (priv->shrinker) {
 		WARN_ON(unregister_vmap_purge_notifier(&priv->vmap_notifier));
-		unregister_shrinker(&priv->shrinker);
+		shrinker_unregister(priv->shrinker);
 	}
 }
-- 
2.30.2

[PATCH v2 24/47] drm/panfrost: dynamically allocate the drm-panfrost shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the drm-panfrost shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct panfrost_device.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/gpu/drm/panfrost/panfrost_device.h    |  2 +-
 drivers/gpu/drm/panfrost/panfrost_drv.c       |  6 +++-
 drivers/gpu/drm/panfrost/panfrost_gem.h       |  2 +-
 .../gpu/drm/panfrost/panfrost_gem_shrinker.c  | 32 ++++++++++++-------
 4 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
index b0126b9fbadc..e667e5689353 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.h
+++ b/drivers/gpu/drm/panfrost/panfrost_device.h
@@ -118,7 +118,7 @@ struct panfrost_device {
 
 	struct mutex shrinker_lock;
 	struct list_head shrinker_list;
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 
 	struct panfrost_devfreq pfdevfreq;
 };
diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
index bbada731bbbd..f705bbdea360 100644
--- a/drivers/gpu/drm/panfrost/panfrost_drv.c
+++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
@@ -598,10 +598,14 @@ static int panfrost_probe(struct platform_device *pdev)
 	if (err < 0)
 		goto err_out1;
 
-	panfrost_gem_shrinker_init(ddev);
+	err = panfrost_gem_shrinker_init(ddev);
+	if (err)
+		goto err_out2;
 
 	return 0;
 
+err_out2:
+	drm_dev_unregister(ddev);
 err_out1:
 	pm_runtime_disable(pfdev->dev);
 	panfrost_device_fini(pfdev);
diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
index ad2877eeeccd..863d2ec8d4f0 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.h
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
@@ -81,7 +81,7 @@ panfrost_gem_mapping_get(struct panfrost_gem_object *bo,
 void panfrost_gem_mapping_put(struct panfrost_gem_mapping *mapping);
 void panfrost_gem_teardown_mappings_locked(struct panfrost_gem_object *bo);
 
-void panfrost_gem_shrinker_init(struct drm_device *dev);
+int panfrost_gem_shrinker_init(struct drm_device *dev);
 void panfrost_gem_shrinker_cleanup(struct drm_device *dev);
 
 #endif /* __PANFROST_GEM_H__ */
diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
index bf0170782f25..9a90dfb5301f 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
@@ -18,8 +18,7 @@
 static unsigned long
 panfrost_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 {
-	struct panfrost_device *pfdev =
-		container_of(shrinker, struct panfrost_device, shrinker);
+	struct panfrost_device *pfdev = shrinker->private_data;
 	struct drm_gem_shmem_object *shmem;
 	unsigned long count = 0;
 
@@ -65,8 +64,7 @@ static bool panfrost_gem_purge(struct drm_gem_object *obj)
 static unsigned long
 panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 {
-	struct panfrost_device *pfdev =
-		container_of(shrinker, struct panfrost_device, shrinker);
+	struct panfrost_device *pfdev = shrinker->private_data;
 	struct drm_gem_shmem_object *shmem, *tmp;
 	unsigned long freed = 0;
 
@@ -97,13 +95,24 @@ panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
  *
  * This function registers and sets up the panfrost shrinker.
  */
-void panfrost_gem_shrinker_init(struct drm_device *dev)
+int panfrost_gem_shrinker_init(struct drm_device *dev)
 {
 	struct panfrost_device *pfdev = dev->dev_private;
-	pfdev->shrinker.count_objects = panfrost_gem_shrinker_count;
-	pfdev->shrinker.scan_objects = panfrost_gem_shrinker_scan;
-	pfdev->shrinker.seeks = DEFAULT_SEEKS;
-	WARN_ON(register_shrinker(&pfdev->shrinker, "drm-panfrost"));
+
+	pfdev->shrinker = shrinker_alloc(0, "drm-panfrost");
+	if (!pfdev->shrinker) {
+		WARN_ON(1);
+		return -ENOMEM;
+	}
+
+	pfdev->shrinker->count_objects = panfrost_gem_shrinker_count;
+	pfdev->shrinker->scan_objects = panfrost_gem_shrinker_scan;
+	pfdev->shrinker->seeks = DEFAULT_SEEKS;
+	pfdev->shrinker->private_data = pfdev;
+
+	shrinker_register(pfdev->shrinker);
+
+	return 0;
 }
 
 /**
@@ -116,7 +125,6 @@ void panfrost_gem_shrinker_cleanup(struct drm_device *dev)
 {
 	struct panfrost_device *pfdev = dev->dev_private;
 
-	if (pfdev->shrinker.nr_deferred) {
-		unregister_shrinker(&pfdev->shrinker);
-	}
+	if (pfdev->shrinker)
+		shrinker_unregister(pfdev->shrinker);
 }
-- 
2.30.2

[PATCH v2 25/47] dm: dynamically allocate the dm-bufio shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the dm-bufio shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct dm_bufio_client.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/md/dm-bufio.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index bc309e41d074..028e30a4b2d0 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -963,7 +963,7 @@ struct dm_bufio_client {
 
 	sector_t start;
 
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 	struct work_struct shrink_work;
 	atomic_long_t need_shrink;
 
@@ -2368,7 +2368,7 @@ static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink
 {
 	struct dm_bufio_client *c;
 
-	c = container_of(shrink, struct dm_bufio_client, shrinker);
+	c = shrink->private_data;
 	atomic_long_add(sc->nr_to_scan, &c->need_shrink);
 	queue_work(dm_bufio_wq, &c->shrink_work);
 
@@ -2377,7 +2377,7 @@ static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink
 
 static unsigned long dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
-	struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
+	struct dm_bufio_client *c = shrink->private_data;
 	unsigned long count = cache_total(&c->cache);
 	unsigned long retain_target = get_retain_buffers(c);
 	unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);
@@ -2490,15 +2490,19 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
 	INIT_WORK(&c->shrink_work, shrink_work);
 	atomic_long_set(&c->need_shrink, 0);
 
-	c->shrinker.count_objects = dm_bufio_shrink_count;
-	c->shrinker.scan_objects = dm_bufio_shrink_scan;
-	c->shrinker.seeks = 1;
-	c->shrinker.batch = 0;
-	r = register_shrinker(&c->shrinker, "dm-bufio:(%u:%u)",
-			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
-	if (r)
+	c->shrinker = shrinker_alloc(0, "dm-bufio:(%u:%u)",
+				     MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
+	if (!c->shrinker)
 		goto bad;
 
+	c->shrinker->count_objects = dm_bufio_shrink_count;
+	c->shrinker->scan_objects = dm_bufio_shrink_scan;
+	c->shrinker->seeks = 1;
+	c->shrinker->batch = 0;
+	c->shrinker->private_data = c;
+
+	shrinker_register(c->shrinker);
+
 	mutex_lock(&dm_bufio_clients_lock);
 	dm_bufio_client_count++;
 	list_add(&c->client_list, &dm_bufio_all_clients);
@@ -2537,7 +2541,7 @@ void dm_bufio_client_destroy(struct dm_bufio_client *c)
 
 	drop_buffers(c);
 
-	unregister_shrinker(&c->shrinker);
+	shrinker_unregister(c->shrinker);
 	flush_work(&c->shrink_work);
 
 	mutex_lock(&dm_bufio_clients_lock);
-- 
2.30.2

[PATCH v2 26/47] dm zoned: dynamically allocate the dm-zoned-meta shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the dm-zoned-meta shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct dmz_metadata.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/md/dm-zoned-metadata.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
index 9d3cca8e3dc9..657f274e4e84 100644
--- a/drivers/md/dm-zoned-metadata.c
+++ b/drivers/md/dm-zoned-metadata.c
@@ -187,7 +187,7 @@ struct dmz_metadata {
 	struct rb_root		mblk_rbtree;
 	struct list_head	mblk_lru_list;
 	struct list_head	mblk_dirty_list;
-	struct shrinker		mblk_shrinker;
+	struct shrinker		*mblk_shrinker;
 
 	/* Zone allocation management */
 	struct mutex		map_lock;
@@ -615,7 +615,7 @@ static unsigned long dmz_shrink_mblock_cache(struct dmz_metadata *zmd,
 static unsigned long dmz_mblock_shrinker_count(struct shrinker *shrink,
 					       struct shrink_control *sc)
 {
-	struct dmz_metadata *zmd = container_of(shrink, struct dmz_metadata, mblk_shrinker);
+	struct dmz_metadata *zmd = shrink->private_data;
 
 	return atomic_read(&zmd->nr_mblks);
 }
@@ -626,7 +626,7 @@ static unsigned long dmz_mblock_shrinker_count(struct shrinker *shrink,
 static unsigned long dmz_mblock_shrinker_scan(struct shrinker *shrink,
 					      struct shrink_control *sc)
 {
-	struct dmz_metadata *zmd = container_of(shrink, struct dmz_metadata, mblk_shrinker);
+	struct dmz_metadata *zmd = shrink->private_data;
 	unsigned long count;
 
 	spin_lock(&zmd->mblk_lock);
@@ -2936,19 +2936,23 @@ int dmz_ctr_metadata(struct dmz_dev *dev, int num_dev,
 	 */
 	zmd->min_nr_mblks = 2 + zmd->nr_map_blocks + zmd->zone_nr_bitmap_blocks * 16;
 	zmd->max_nr_mblks = zmd->min_nr_mblks + 512;
-	zmd->mblk_shrinker.count_objects = dmz_mblock_shrinker_count;
-	zmd->mblk_shrinker.scan_objects = dmz_mblock_shrinker_scan;
-	zmd->mblk_shrinker.seeks = DEFAULT_SEEKS;
 
 	/* Metadata cache shrinker */
-	ret = register_shrinker(&zmd->mblk_shrinker, "dm-zoned-meta:(%u:%u)",
-				MAJOR(dev->bdev->bd_dev),
-				MINOR(dev->bdev->bd_dev));
-	if (ret) {
-		dmz_zmd_err(zmd, "Register metadata cache shrinker failed");
+	zmd->mblk_shrinker = shrinker_alloc(0,  "dm-zoned-meta:(%u:%u)",
+					    MAJOR(dev->bdev->bd_dev),
+					    MINOR(dev->bdev->bd_dev));
+	if (!zmd->mblk_shrinker) {
+		dmz_zmd_err(zmd, "Allocate metadata cache shrinker failed");
 		goto err;
 	}
 
+	zmd->mblk_shrinker->count_objects = dmz_mblock_shrinker_count;
+	zmd->mblk_shrinker->scan_objects = dmz_mblock_shrinker_scan;
+	zmd->mblk_shrinker->seeks = DEFAULT_SEEKS;
+	zmd->mblk_shrinker->private_data = zmd;
+
+	shrinker_register(zmd->mblk_shrinker);
+
 	dmz_zmd_info(zmd, "DM-Zoned metadata version %d", zmd->sb_version);
 	for (i = 0; i < zmd->nr_devs; i++)
 		dmz_print_dev(zmd, i);
@@ -2995,7 +2999,7 @@ int dmz_ctr_metadata(struct dmz_dev *dev, int num_dev,
  */
 void dmz_dtr_metadata(struct dmz_metadata *zmd)
 {
-	unregister_shrinker(&zmd->mblk_shrinker);
+	shrinker_unregister(zmd->mblk_shrinker);
 	dmz_cleanup_metadata(zmd);
 	kfree(zmd);
 }
-- 
2.30.2

[PATCH v2 27/47] md/raid5: dynamically allocate the md-raid5 shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the md-raid5 shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct r5conf.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/md/raid5.c | 25 ++++++++++++++-----------
 drivers/md/raid5.h |  2 +-
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 85b3004594e0..12443dfb7aeb 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7414,7 +7414,7 @@ static void free_conf(struct r5conf *conf)
 
 	log_exit(conf);
 
-	unregister_shrinker(&conf->shrinker);
+	shrinker_unregister(conf->shrinker);
 	free_thread_groups(conf);
 	shrink_stripes(conf);
 	raid5_free_percpu(conf);
@@ -7462,7 +7462,7 @@ static int raid5_alloc_percpu(struct r5conf *conf)
 static unsigned long raid5_cache_scan(struct shrinker *shrink,
 				      struct shrink_control *sc)
 {
-	struct r5conf *conf = container_of(shrink, struct r5conf, shrinker);
+	struct r5conf *conf = shrink->private_data;
 	unsigned long ret = SHRINK_STOP;
 
 	if (mutex_trylock(&conf->cache_size_mutex)) {
@@ -7483,7 +7483,7 @@ static unsigned long raid5_cache_scan(struct shrinker *shrink,
 static unsigned long raid5_cache_count(struct shrinker *shrink,
 				       struct shrink_control *sc)
 {
-	struct r5conf *conf = container_of(shrink, struct r5conf, shrinker);
+	struct r5conf *conf = shrink->private_data;
 
 	if (conf->max_nr_stripes < conf->min_nr_stripes)
 		/* unlikely, but not impossible */
@@ -7718,18 +7718,21 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	 * it reduces the queue depth and so can hurt throughput.
 	 * So set it rather large, scaled by number of devices.
 	 */
-	conf->shrinker.seeks = DEFAULT_SEEKS * conf->raid_disks * 4;
-	conf->shrinker.scan_objects = raid5_cache_scan;
-	conf->shrinker.count_objects = raid5_cache_count;
-	conf->shrinker.batch = 128;
-	conf->shrinker.flags = 0;
-	ret = register_shrinker(&conf->shrinker, "md-raid5:%s", mdname(mddev));
-	if (ret) {
-		pr_warn("md/raid:%s: couldn't register shrinker.\n",
+	conf->shrinker = shrinker_alloc(0, "md-raid5:%s", mdname(mddev));
+	if (!conf->shrinker) {
+		pr_warn("md/raid:%s: couldn't allocate shrinker.\n",
 			mdname(mddev));
 		goto abort;
 	}
 
+	conf->shrinker->seeks = DEFAULT_SEEKS * conf->raid_disks * 4;
+	conf->shrinker->scan_objects = raid5_cache_scan;
+	conf->shrinker->count_objects = raid5_cache_count;
+	conf->shrinker->batch = 128;
+	conf->shrinker->private_data = conf;
+
+	shrinker_register(conf->shrinker);
+
 	sprintf(pers_name, "raid%d", mddev->new_level);
 	rcu_assign_pointer(conf->thread,
 			   md_register_thread(raid5d, mddev, pers_name));
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 97a795979a35..22bea20eccbd 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -670,7 +670,7 @@ struct r5conf {
 	wait_queue_head_t	wait_for_stripe;
 	wait_queue_head_t	wait_for_overlap;
 	unsigned long		cache_state;
-	struct shrinker		shrinker;
+	struct shrinker		*shrinker;
 	int			pool_size; /* number of disks in stripeheads in pool */
 	spinlock_t		device_lock;
 	struct disk_info	*disks;
-- 
2.30.2

[PATCH v2 28/47] bcache: dynamically allocate the md-bcache shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the md-bcache shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct cache_set.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/md/bcache/bcache.h |  2 +-
 drivers/md/bcache/btree.c  | 27 ++++++++++++++++-----------
 drivers/md/bcache/sysfs.c  |  3 ++-
 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 5a79bb3c272f..c622bc50f81b 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -541,7 +541,7 @@ struct cache_set {
 	struct bio_set		bio_split;
 
 	/* For the btree cache */
-	struct shrinker		shrink;
+	struct shrinker		*shrink;
 
 	/* For the btree cache and anything allocation related */
 	struct mutex		bucket_lock;
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index fd121a61f17c..c176c7fc77d9 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -667,7 +667,7 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush)
 static unsigned long bch_mca_scan(struct shrinker *shrink,
 				  struct shrink_control *sc)
 {
-	struct cache_set *c = container_of(shrink, struct cache_set, shrink);
+	struct cache_set *c = shrink->private_data;
 	struct btree *b, *t;
 	unsigned long i, nr = sc->nr_to_scan;
 	unsigned long freed = 0;
@@ -734,7 +734,7 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
 static unsigned long bch_mca_count(struct shrinker *shrink,
 				   struct shrink_control *sc)
 {
-	struct cache_set *c = container_of(shrink, struct cache_set, shrink);
+	struct cache_set *c = shrink->private_data;
 
 	if (c->shrinker_disabled)
 		return 0;
@@ -752,8 +752,8 @@ void bch_btree_cache_free(struct cache_set *c)
 
 	closure_init_stack(&cl);
 
-	if (c->shrink.list.next)
-		unregister_shrinker(&c->shrink);
+	if (c->shrink)
+		shrinker_unregister(c->shrink);
 
 	mutex_lock(&c->bucket_lock);
 
@@ -828,14 +828,19 @@ int bch_btree_cache_alloc(struct cache_set *c)
 		c->verify_data = NULL;
 #endif
 
-	c->shrink.count_objects = bch_mca_count;
-	c->shrink.scan_objects = bch_mca_scan;
-	c->shrink.seeks = 4;
-	c->shrink.batch = c->btree_pages * 2;
+	c->shrink = shrinker_alloc(0, "md-bcache:%pU", c->set_uuid);
+	if (!c->shrink) {
+		pr_warn("bcache: %s: could not allocate shrinker\n", __func__);
+		return -ENOMEM;
+	}
+
+	c->shrink->count_objects = bch_mca_count;
+	c->shrink->scan_objects = bch_mca_scan;
+	c->shrink->seeks = 4;
+	c->shrink->batch = c->btree_pages * 2;
+	c->shrink->private_data = c;
 
-	if (register_shrinker(&c->shrink, "md-bcache:%pU", c->set_uuid))
-		pr_warn("bcache: %s: could not register shrinker\n",
-				__func__);
+	shrinker_register(c->shrink);
 
 	return 0;
 }
diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 0e2c1880f60b..45d8af755de6 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -866,7 +866,8 @@ STORE(__bch_cache_set)
 
 		sc.gfp_mask = GFP_KERNEL;
 		sc.nr_to_scan = strtoul_or_return(buf);
-		c->shrink.scan_objects(&c->shrink, &sc);
+		if (c->shrink)
+			c->shrink->scan_objects(c->shrink, &sc);
 	}
 
 	sysfs_strtoul_clamp(congested_read_threshold_us,
-- 
2.30.2

[PATCH v2 29/47] vmw_balloon: dynamically allocate the vmw-balloon shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the vmw-balloon shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct vmballoon.

And we can simply exit vmballoon_init() when registering the shrinker
fails. So the shrinker_registered indication is redundant, just remove it.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/misc/vmw_balloon.c | 38 ++++++++++++--------------------------
 1 file changed, 12 insertions(+), 26 deletions(-)

diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
index 9ce9b9e0e9b6..d216d4dc042e 100644
--- a/drivers/misc/vmw_balloon.c
+++ b/drivers/misc/vmw_balloon.c
@@ -380,16 +380,7 @@ struct vmballoon {
 	/**
 	 * @shrinker: shrinker interface that is used to avoid over-inflation.
 	 */
-	struct shrinker shrinker;
-
-	/**
-	 * @shrinker_registered: whether the shrinker was registered.
-	 *
-	 * The shrinker interface does not handle gracefully the removal of
-	 * shrinker that was not registered before. This indication allows to
-	 * simplify the unregistration process.
-	 */
-	bool shrinker_registered;
+	struct shrinker *shrinker;
 };
 
 static struct vmballoon balloon;
@@ -1568,29 +1559,27 @@ static unsigned long vmballoon_shrinker_count(struct shrinker *shrinker,
 
 static void vmballoon_unregister_shrinker(struct vmballoon *b)
 {
-	if (b->shrinker_registered)
-		unregister_shrinker(&b->shrinker);
-	b->shrinker_registered = false;
+	shrinker_unregister(b->shrinker);
 }
 
 static int vmballoon_register_shrinker(struct vmballoon *b)
 {
-	int r;
-
 	/* Do nothing if the shrinker is not enabled */
 	if (!vmwballoon_shrinker_enable)
 		return 0;
 
-	b->shrinker.scan_objects = vmballoon_shrinker_scan;
-	b->shrinker.count_objects = vmballoon_shrinker_count;
-	b->shrinker.seeks = DEFAULT_SEEKS;
+	b->shrinker = shrinker_alloc(0, "vmw-balloon");
+	if (!b->shrinker)
+		return -ENOMEM;
 
-	r = register_shrinker(&b->shrinker, "vmw-balloon");
+	b->shrinker->scan_objects = vmballoon_shrinker_scan;
+	b->shrinker->count_objects = vmballoon_shrinker_count;
+	b->shrinker->seeks = DEFAULT_SEEKS;
+	b->shrinker->private_data = b;
 
-	if (r == 0)
-		b->shrinker_registered = true;
+	shrinker_register(b->shrinker);
 
-	return r;
+	return 0;
 }
 
 /*
@@ -1883,7 +1872,7 @@ static int __init vmballoon_init(void)
 
 	error = vmballoon_register_shrinker(&balloon);
 	if (error)
-		goto fail;
+		return error;
 
 	/*
 	 * Initialization of compaction must be done after the call to
@@ -1905,9 +1894,6 @@ static int __init vmballoon_init(void)
 	vmballoon_debugfs_init(&balloon);
 
 	return 0;
-fail:
-	vmballoon_unregister_shrinker(&balloon);
-	return error;
 }
 
 /*
-- 
2.30.2

[PATCH v2 30/47] virtio_balloon: dynamically allocate the virtio-balloon shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the virtio-balloon shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct virtio_balloon.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/virtio/virtio_balloon.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 5b15936a5214..d773860c3b18 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -111,7 +111,7 @@ struct virtio_balloon {
 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 
 	/* Shrinker to return free pages - VIRTIO_BALLOON_F_FREE_PAGE_HINT */
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 
 	/* OOM notifier to deflate on OOM - VIRTIO_BALLOON_F_DEFLATE_ON_OOM */
 	struct notifier_block oom_nb;
@@ -816,8 +816,7 @@ static unsigned long shrink_free_pages(struct virtio_balloon *vb,
 static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 						  struct shrink_control *sc)
 {
-	struct virtio_balloon *vb = container_of(shrinker,
-					struct virtio_balloon, shrinker);
+	struct virtio_balloon *vb = shrinker->private_data;
 
 	return shrink_free_pages(vb, sc->nr_to_scan);
 }
@@ -825,8 +824,7 @@ static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
 						   struct shrink_control *sc)
 {
-	struct virtio_balloon *vb = container_of(shrinker,
-					struct virtio_balloon, shrinker);
+	struct virtio_balloon *vb = shrinker->private_data;
 
 	return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
 }
@@ -847,16 +845,23 @@ static int virtio_balloon_oom_notify(struct notifier_block *nb,
 
 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
 {
-	unregister_shrinker(&vb->shrinker);
+	shrinker_unregister(vb->shrinker);
 }
 
 static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
 {
-	vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
-	vb->shrinker.count_objects = virtio_balloon_shrinker_count;
-	vb->shrinker.seeks = DEFAULT_SEEKS;
+	vb->shrinker = shrinker_alloc(0, "virtio-balloon");
+	if (!vb->shrinker)
+		return -ENOMEM;
 
-	return register_shrinker(&vb->shrinker, "virtio-balloon");
+	vb->shrinker->scan_objects = virtio_balloon_shrinker_scan;
+	vb->shrinker->count_objects = virtio_balloon_shrinker_count;
+	vb->shrinker->seeks = DEFAULT_SEEKS;
+	vb->shrinker->private_data = vb;
+
+	shrinker_register(vb->shrinker);
+
+	return 0;
 }
 
 static int virtballoon_probe(struct virtio_device *vdev)
-- 
2.30.2

[PATCH v2 31/47] mbcache: dynamically allocate the mbcache shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the mbcache shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct mb_cache.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/mbcache.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/fs/mbcache.c b/fs/mbcache.c
index 2a4b8b549e93..bfecebeec828 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -37,7 +37,7 @@ struct mb_cache {
 	struct list_head	c_list;
 	/* Number of entries in cache */
 	unsigned long		c_entry_count;
-	struct shrinker		c_shrink;
+	struct shrinker		*c_shrink;
 	/* Work for shrinking when the cache has too many entries */
 	struct work_struct	c_shrink_work;
 };
@@ -293,8 +293,7 @@ EXPORT_SYMBOL(mb_cache_entry_touch);
 static unsigned long mb_cache_count(struct shrinker *shrink,
 				    struct shrink_control *sc)
 {
-	struct mb_cache *cache = container_of(shrink, struct mb_cache,
-					      c_shrink);
+	struct mb_cache *cache = shrink->private_data;
 
 	return cache->c_entry_count;
 }
@@ -333,8 +332,7 @@ static unsigned long mb_cache_shrink(struct mb_cache *cache,
 static unsigned long mb_cache_scan(struct shrinker *shrink,
 				   struct shrink_control *sc)
 {
-	struct mb_cache *cache = container_of(shrink, struct mb_cache,
-					      c_shrink);
+	struct mb_cache *cache = shrink->private_data;
 	return mb_cache_shrink(cache, sc->nr_to_scan);
 }
 
@@ -377,15 +375,20 @@ struct mb_cache *mb_cache_create(int bucket_bits)
 	for (i = 0; i < bucket_count; i++)
 		INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
 
-	cache->c_shrink.count_objects = mb_cache_count;
-	cache->c_shrink.scan_objects = mb_cache_scan;
-	cache->c_shrink.seeks = DEFAULT_SEEKS;
-	if (register_shrinker(&cache->c_shrink, "mbcache-shrinker")) {
+	cache->c_shrink = shrinker_alloc(0, "mbcache-shrinker");
+	if (!cache->c_shrink) {
 		kfree(cache->c_hash);
 		kfree(cache);
 		goto err_out;
 	}
 
+	cache->c_shrink->count_objects = mb_cache_count;
+	cache->c_shrink->scan_objects = mb_cache_scan;
+	cache->c_shrink->seeks = DEFAULT_SEEKS;
+	cache->c_shrink->private_data = cache;
+
+	shrinker_register(cache->c_shrink);
+
 	INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
 
 	return cache;
@@ -406,7 +409,7 @@ void mb_cache_destroy(struct mb_cache *cache)
 {
 	struct mb_cache_entry *entry, *next;
 
-	unregister_shrinker(&cache->c_shrink);
+	shrinker_unregister(cache->c_shrink);
 
 	/*
 	 * We don't bother with any locking. Cache must not be used at this
-- 
2.30.2

[PATCH v2 32/47] ext4: dynamically allocate the ext4-es shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the ext4-es shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct ext4_sb_info.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/ext4/ext4.h           |  2 +-
 fs/ext4/extents_status.c | 22 ++++++++++++----------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0a2d55faa095..1bd150d454f5 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1651,7 +1651,7 @@ struct ext4_sb_info {
 	__u32 s_csum_seed;
 
 	/* Reclaim extents from extent status tree */
-	struct shrinker s_es_shrinker;
+	struct shrinker *s_es_shrinker;
 	struct list_head s_es_list;	/* List of inodes with reclaimable extents */
 	long s_es_nr_inode;
 	struct ext4_es_stats s_es_stats;
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 9b5b8951afb4..8d4a959dd32f 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -1596,7 +1596,7 @@ static unsigned long ext4_es_count(struct shrinker *shrink,
 	unsigned long nr;
 	struct ext4_sb_info *sbi;
 
-	sbi = container_of(shrink, struct ext4_sb_info, s_es_shrinker);
+	sbi = shrink->private_data;
 	nr = percpu_counter_read_positive(&sbi->s_es_stats.es_stats_shk_cnt);
 	trace_ext4_es_shrink_count(sbi->s_sb, sc->nr_to_scan, nr);
 	return nr;
@@ -1605,8 +1605,7 @@ static unsigned long ext4_es_count(struct shrinker *shrink,
 static unsigned long ext4_es_scan(struct shrinker *shrink,
 				  struct shrink_control *sc)
 {
-	struct ext4_sb_info *sbi = container_of(shrink,
-					struct ext4_sb_info, s_es_shrinker);
+	struct ext4_sb_info *sbi = shrink->private_data;
 	int nr_to_scan = sc->nr_to_scan;
 	int ret, nr_shrunk;
 
@@ -1690,14 +1689,17 @@ int ext4_es_register_shrinker(struct ext4_sb_info *sbi)
 	if (err)
 		goto err3;
 
-	sbi->s_es_shrinker.scan_objects = ext4_es_scan;
-	sbi->s_es_shrinker.count_objects = ext4_es_count;
-	sbi->s_es_shrinker.seeks = DEFAULT_SEEKS;
-	err = register_shrinker(&sbi->s_es_shrinker, "ext4-es:%s",
-				sbi->s_sb->s_id);
-	if (err)
+	sbi->s_es_shrinker = shrinker_alloc(0, "ext4-es:%s", sbi->s_sb->s_id);
+	if (!sbi->s_es_shrinker)
 		goto err4;
 
+	sbi->s_es_shrinker->scan_objects = ext4_es_scan;
+	sbi->s_es_shrinker->count_objects = ext4_es_count;
+	sbi->s_es_shrinker->seeks = DEFAULT_SEEKS;
+	sbi->s_es_shrinker->private_data = sbi;
+
+	shrinker_register(sbi->s_es_shrinker);
+
 	return 0;
 err4:
 	percpu_counter_destroy(&sbi->s_es_stats.es_stats_shk_cnt);
@@ -1716,7 +1718,7 @@ void ext4_es_unregister_shrinker(struct ext4_sb_info *sbi)
 	percpu_counter_destroy(&sbi->s_es_stats.es_stats_cache_misses);
 	percpu_counter_destroy(&sbi->s_es_stats.es_stats_all_cnt);
 	percpu_counter_destroy(&sbi->s_es_stats.es_stats_shk_cnt);
-	unregister_shrinker(&sbi->s_es_shrinker);
+	shrinker_unregister(sbi->s_es_shrinker);
 }
 
 /*
-- 
2.30.2

[PATCH v2 33/47] jbd2, ext4: dynamically allocate the jbd2-journal shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the jbd2-journal shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct journal_s.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/jbd2/journal.c    | 27 +++++++++++++++++----------
 include/linux/jbd2.h |  2 +-
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index fbce16fedaa4..a7d555ea06e3 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1301,7 +1301,7 @@ static int jbd2_min_tag_size(void)
 static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
 					      struct shrink_control *sc)
 {
-	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
+	journal_t *journal = shrink->private_data;
 	unsigned long nr_to_scan = sc->nr_to_scan;
 	unsigned long nr_shrunk;
 	unsigned long count;
@@ -1327,7 +1327,7 @@ static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
 static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
 					       struct shrink_control *sc)
 {
-	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
+	journal_t *journal = shrink->private_data;
 	unsigned long count;
 
 	count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
@@ -1415,19 +1415,26 @@ static journal_t *journal_init_common(struct block_device *bdev,
 	journal->j_superblock = (journal_superblock_t *)bh->b_data;
 
 	journal->j_shrink_transaction = NULL;
-	journal->j_shrinker.scan_objects = jbd2_journal_shrink_scan;
-	journal->j_shrinker.count_objects = jbd2_journal_shrink_count;
-	journal->j_shrinker.seeks = DEFAULT_SEEKS;
-	journal->j_shrinker.batch = journal->j_max_transaction_buffers;
 
 	if (percpu_counter_init(&journal->j_checkpoint_jh_count, 0, GFP_KERNEL))
 		goto err_cleanup;
 
-	if (register_shrinker(&journal->j_shrinker, "jbd2-journal:(%u:%u)",
-			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev))) {
+	journal->j_shrinker = shrinker_alloc(0, "jbd2-journal:(%u:%u)",
+					     MAJOR(bdev->bd_dev),
+					     MINOR(bdev->bd_dev));
+	if (!journal->j_shrinker) {
 		percpu_counter_destroy(&journal->j_checkpoint_jh_count);
 		goto err_cleanup;
 	}
+
+	journal->j_shrinker->scan_objects = jbd2_journal_shrink_scan;
+	journal->j_shrinker->count_objects = jbd2_journal_shrink_count;
+	journal->j_shrinker->seeks = DEFAULT_SEEKS;
+	journal->j_shrinker->batch = journal->j_max_transaction_buffers;
+	journal->j_shrinker->private_data = journal;
+
+	shrinker_register(journal->j_shrinker);
+
 	return journal;
 
 err_cleanup:
@@ -2190,9 +2197,9 @@ int jbd2_journal_destroy(journal_t *journal)
 		brelse(journal->j_sb_buffer);
 	}
 
-	if (journal->j_shrinker.flags & SHRINKER_REGISTERED) {
+	if (journal->j_shrinker) {
 		percpu_counter_destroy(&journal->j_checkpoint_jh_count);
-		unregister_shrinker(&journal->j_shrinker);
+		shrinker_unregister(journal->j_shrinker);
 	}
 	if (journal->j_proc_entry)
 		jbd2_stats_proc_exit(journal);
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index d860499e15e4..9fdc02565c24 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -897,7 +897,7 @@ struct journal_s
 	 * Journal head shrinker, reclaim buffer's journal head which
 	 * has been written back.
 	 */
-	struct shrinker		j_shrinker;
+	struct shrinker		*j_shrinker;
 
 	/**
 	 * @j_checkpoint_jh_count:
-- 
2.30.2

[PATCH v2 34/47] nfsd: dynamically allocate the nfsd-client shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the nfsd-client shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct nfsd_net.

Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/nfsd/netns.h     |  2 +-
 fs/nfsd/nfs4state.c | 20 ++++++++++++--------
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index ec49b200b797..f669444d5336 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -195,7 +195,7 @@ struct nfsd_net {
 	int			nfs4_max_clients;
 
 	atomic_t		nfsd_courtesy_clients;
-	struct shrinker		nfsd_client_shrinker;
+	struct shrinker		*nfsd_client_shrinker;
 	struct work_struct	nfsd_shrinker_work;
 };
 
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 3339177f8e2f..c7a4616cd866 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4388,8 +4388,7 @@ static unsigned long
 nfsd4_state_shrinker_count(struct shrinker *shrink, struct shrink_control *sc)
 {
 	int count;
-	struct nfsd_net *nn = container_of(shrink,
-			struct nfsd_net, nfsd_client_shrinker);
+	struct nfsd_net *nn = shrink->private_data;
 
 	count = atomic_read(&nn->nfsd_courtesy_clients);
 	if (!count)
@@ -8125,12 +8124,17 @@ static int nfs4_state_create_net(struct net *net)
 	INIT_WORK(&nn->nfsd_shrinker_work, nfsd4_state_shrinker_worker);
 	get_net(net);
 
-	nn->nfsd_client_shrinker.scan_objects = nfsd4_state_shrinker_scan;
-	nn->nfsd_client_shrinker.count_objects = nfsd4_state_shrinker_count;
-	nn->nfsd_client_shrinker.seeks = DEFAULT_SEEKS;
-
-	if (register_shrinker(&nn->nfsd_client_shrinker, "nfsd-client"))
+	nn->nfsd_client_shrinker = shrinker_alloc(0, "nfsd-client");
+	if (!nn->nfsd_client_shrinker)
 		goto err_shrinker;
+
+	nn->nfsd_client_shrinker->scan_objects = nfsd4_state_shrinker_scan;
+	nn->nfsd_client_shrinker->count_objects = nfsd4_state_shrinker_count;
+	nn->nfsd_client_shrinker->seeks = DEFAULT_SEEKS;
+	nn->nfsd_client_shrinker->private_data = nn;
+
+	shrinker_register(nn->nfsd_client_shrinker);
+
 	return 0;
 
 err_shrinker:
@@ -8228,7 +8232,7 @@ nfs4_state_shutdown_net(struct net *net)
 	struct list_head *pos, *next, reaplist;
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	unregister_shrinker(&nn->nfsd_client_shrinker);
+	shrinker_unregister(nn->nfsd_client_shrinker);
 	cancel_work(&nn->nfsd_shrinker_work);
 	cancel_delayed_work_sync(&nn->laundromat_work);
 	locks_end_grace(&nn->nfsd4_manager);
-- 
2.30.2

[PATCH v2 35/47] nfsd: dynamically allocate the nfsd-reply shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the nfsd-reply shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct nfsd_net.

Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/nfsd/netns.h    |  2 +-
 fs/nfsd/nfscache.c | 31 ++++++++++++++++---------------
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index f669444d5336..ab303a8b77d5 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -177,7 +177,7 @@ struct nfsd_net {
 	/* size of cache when we saw the longest hash chain */
 	unsigned int             longest_chain_cachesize;
 
-	struct shrinker		nfsd_reply_cache_shrinker;
+	struct shrinker		*nfsd_reply_cache_shrinker;
 
 	/* tracking server-to-server copy mounts */
 	spinlock_t              nfsd_ssc_lock;
diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index 6eb3d7bdfaf3..9f0ab65e4125 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -200,26 +200,29 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
 {
 	unsigned int hashsize;
 	unsigned int i;
-	int status = 0;
 
 	nn->max_drc_entries = nfsd_cache_size_limit();
 	atomic_set(&nn->num_drc_entries, 0);
 	hashsize = nfsd_hashsize(nn->max_drc_entries);
 	nn->maskbits = ilog2(hashsize);
 
-	nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
-	nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
-	nn->nfsd_reply_cache_shrinker.seeks = 1;
-	status = register_shrinker(&nn->nfsd_reply_cache_shrinker,
-				   "nfsd-reply:%s", nn->nfsd_name);
-	if (status)
-		return status;
-
 	nn->drc_hashtbl = kvzalloc(array_size(hashsize,
 				sizeof(*nn->drc_hashtbl)), GFP_KERNEL);
 	if (!nn->drc_hashtbl)
+		return -ENOMEM;
+
+	nn->nfsd_reply_cache_shrinker = shrinker_alloc(0, "nfsd-reply:%s",
+						       nn->nfsd_name);
+	if (!nn->nfsd_reply_cache_shrinker)
 		goto out_shrinker;
 
+	nn->nfsd_reply_cache_shrinker->scan_objects = nfsd_reply_cache_scan;
+	nn->nfsd_reply_cache_shrinker->count_objects = nfsd_reply_cache_count;
+	nn->nfsd_reply_cache_shrinker->seeks = 1;
+	nn->nfsd_reply_cache_shrinker->private_data = nn;
+
+	shrinker_register(nn->nfsd_reply_cache_shrinker);
+
 	for (i = 0; i < hashsize; i++) {
 		INIT_LIST_HEAD(&nn->drc_hashtbl[i].lru_head);
 		spin_lock_init(&nn->drc_hashtbl[i].cache_lock);
@@ -228,7 +231,7 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
 
 	return 0;
 out_shrinker:
-	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
+	kvfree(nn->drc_hashtbl);
 	printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
 	return -ENOMEM;
 }
@@ -238,7 +241,7 @@ void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
 	struct nfsd_cacherep *rp;
 	unsigned int i;
 
-	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
+	shrinker_unregister(nn->nfsd_reply_cache_shrinker);
 
 	for (i = 0; i < nn->drc_hashsize; i++) {
 		struct list_head *head = &nn->drc_hashtbl[i].lru_head;
@@ -322,8 +325,7 @@ nfsd_prune_bucket_locked(struct nfsd_net *nn, struct nfsd_drc_bucket *b,
 static unsigned long
 nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
 {
-	struct nfsd_net *nn = container_of(shrink,
-				struct nfsd_net, nfsd_reply_cache_shrinker);
+	struct nfsd_net *nn = shrink->private_data;
 
 	return atomic_read(&nn->num_drc_entries);
 }
@@ -342,8 +344,7 @@ nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
 static unsigned long
 nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
 {
-	struct nfsd_net *nn = container_of(shrink,
-				struct nfsd_net, nfsd_reply_cache_shrinker);
+	struct nfsd_net *nn = shrink->private_data;
 	unsigned long freed = 0;
 	LIST_HEAD(dispose);
 	unsigned int i;
-- 
2.30.2

[PATCH v2 36/47] xfs: dynamically allocate the xfs-buf shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the xfs-buf shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct xfs_buftarg.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/xfs/xfs_buf.c | 25 ++++++++++++++-----------
 fs/xfs/xfs_buf.h |  2 +-
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 15d1e5a7c2d3..19a0bf6ce115 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1906,8 +1906,7 @@ xfs_buftarg_shrink_scan(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_buftarg	*btp = container_of(shrink,
-					struct xfs_buftarg, bt_shrinker);
+	struct xfs_buftarg	*btp = shrink->private_data;
 	LIST_HEAD(dispose);
 	unsigned long		freed;
 
@@ -1929,8 +1928,7 @@ xfs_buftarg_shrink_count(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_buftarg	*btp = container_of(shrink,
-					struct xfs_buftarg, bt_shrinker);
+	struct xfs_buftarg	*btp = shrink->private_data;
 	return list_lru_shrink_count(&btp->bt_lru, sc);
 }
 
@@ -1938,7 +1936,7 @@ void
 xfs_free_buftarg(
 	struct xfs_buftarg	*btp)
 {
-	unregister_shrinker(&btp->bt_shrinker);
+	shrinker_unregister(btp->bt_shrinker);
 	ASSERT(percpu_counter_sum(&btp->bt_io_count) == 0);
 	percpu_counter_destroy(&btp->bt_io_count);
 	list_lru_destroy(&btp->bt_lru);
@@ -2021,13 +2019,18 @@ xfs_alloc_buftarg(
 	if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
 		goto error_lru;
 
-	btp->bt_shrinker.count_objects = xfs_buftarg_shrink_count;
-	btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
-	btp->bt_shrinker.seeks = DEFAULT_SEEKS;
-	btp->bt_shrinker.flags = SHRINKER_NUMA_AWARE;
-	if (register_shrinker(&btp->bt_shrinker, "xfs-buf:%s",
-			      mp->m_super->s_id))
+	btp->bt_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE, "xfs-buf:%s",
+					  mp->m_super->s_id);
+	if (!btp->bt_shrinker)
 		goto error_pcpu;
+
+	btp->bt_shrinker->count_objects = xfs_buftarg_shrink_count;
+	btp->bt_shrinker->scan_objects = xfs_buftarg_shrink_scan;
+	btp->bt_shrinker->seeks = DEFAULT_SEEKS;
+	btp->bt_shrinker->private_data = btp;
+
+	shrinker_register(btp->bt_shrinker);
+
 	return btp;
 
 error_pcpu:
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 549c60942208..4e6969a675f7 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -102,7 +102,7 @@ typedef struct xfs_buftarg {
 	size_t			bt_logical_sectormask;
 
 	/* LRU control structures */
-	struct shrinker		bt_shrinker;
+	struct shrinker		*bt_shrinker;
 	struct list_lru		bt_lru;
 
 	struct percpu_counter	bt_io_count;
-- 
2.30.2

[PATCH v2 37/47] xfs: dynamically allocate the xfs-inodegc shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the xfs-inodegc shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct xfs_mount.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/xfs/xfs_icache.c | 26 +++++++++++++++-----------
 fs/xfs/xfs_mount.c  |  4 ++--
 fs/xfs/xfs_mount.h  |  2 +-
 3 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 453890942d9f..751c380afd5a 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -2225,8 +2225,7 @@ xfs_inodegc_shrinker_count(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_mount	*mp = container_of(shrink, struct xfs_mount,
-						   m_inodegc_shrinker);
+	struct xfs_mount	*mp = shrink->private_data;
 	struct xfs_inodegc	*gc;
 	int			cpu;
 
@@ -2247,8 +2246,7 @@ xfs_inodegc_shrinker_scan(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_mount	*mp = container_of(shrink, struct xfs_mount,
-						   m_inodegc_shrinker);
+	struct xfs_mount	*mp = shrink->private_data;
 	struct xfs_inodegc	*gc;
 	int			cpu;
 	bool			no_items = true;
@@ -2284,13 +2282,19 @@ int
 xfs_inodegc_register_shrinker(
 	struct xfs_mount	*mp)
 {
-	struct shrinker		*shrink = &mp->m_inodegc_shrinker;
+	mp->m_inodegc_shrinker = shrinker_alloc(SHRINKER_NONSLAB,
+						"xfs-inodegc:%s",
+						mp->m_super->s_id);
+	if (!mp->m_inodegc_shrinker)
+		return -ENOMEM;
+
+	mp->m_inodegc_shrinker->count_objects = xfs_inodegc_shrinker_count;
+	mp->m_inodegc_shrinker->scan_objects = xfs_inodegc_shrinker_scan;
+	mp->m_inodegc_shrinker->seeks = 0;
+	mp->m_inodegc_shrinker->batch = XFS_INODEGC_SHRINKER_BATCH;
+	mp->m_inodegc_shrinker->private_data = mp;
 
-	shrink->count_objects = xfs_inodegc_shrinker_count;
-	shrink->scan_objects = xfs_inodegc_shrinker_scan;
-	shrink->seeks = 0;
-	shrink->flags = SHRINKER_NONSLAB;
-	shrink->batch = XFS_INODEGC_SHRINKER_BATCH;
+	shrinker_register(mp->m_inodegc_shrinker);
 
-	return register_shrinker(shrink, "xfs-inodegc:%s", mp->m_super->s_id);
+	return 0;
 }
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index fb87ffb48f7f..27c2d24797c9 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1018,7 +1018,7 @@ xfs_mountfs(
  out_log_dealloc:
 	xfs_log_mount_cancel(mp);
  out_inodegc_shrinker:
-	unregister_shrinker(&mp->m_inodegc_shrinker);
+	shrinker_unregister(mp->m_inodegc_shrinker);
  out_fail_wait:
 	if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp)
 		xfs_buftarg_drain(mp->m_logdev_targp);
@@ -1100,7 +1100,7 @@ xfs_unmountfs(
 #if defined(DEBUG)
 	xfs_errortag_clearall(mp);
 #endif
-	unregister_shrinker(&mp->m_inodegc_shrinker);
+	shrinker_unregister(mp->m_inodegc_shrinker);
 	xfs_free_perag(mp);
 
 	xfs_errortag_del(mp);
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index e2866e7fa60c..562c294ca08e 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -217,7 +217,7 @@ typedef struct xfs_mount {
 	atomic_t		m_agirotor;	/* last ag dir inode alloced */
 
 	/* Memory shrinker to throttle and reprioritize inodegc */
-	struct shrinker		m_inodegc_shrinker;
+	struct shrinker		*m_inodegc_shrinker;
 	/*
 	 * Workqueue item so that we can coalesce multiple inode flush attempts
 	 * into a single flush.
-- 
2.30.2

[PATCH v2 38/47] xfs: dynamically allocate the xfs-qm shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the xfs-qm shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct xfs_quotainfo.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/xfs/xfs_qm.c | 26 +++++++++++++-------------
 fs/xfs/xfs_qm.h |  2 +-
 2 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 6abcc34fafd8..8f1216e1efc1 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -504,8 +504,7 @@ xfs_qm_shrink_scan(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_quotainfo	*qi = container_of(shrink,
-					struct xfs_quotainfo, qi_shrinker);
+	struct xfs_quotainfo	*qi = shrink->private_data;
 	struct xfs_qm_isolate	isol;
 	unsigned long		freed;
 	int			error;
@@ -539,8 +538,7 @@ xfs_qm_shrink_count(
 	struct shrinker		*shrink,
 	struct shrink_control	*sc)
 {
-	struct xfs_quotainfo	*qi = container_of(shrink,
-					struct xfs_quotainfo, qi_shrinker);
+	struct xfs_quotainfo	*qi = shrink->private_data;
 
 	return list_lru_shrink_count(&qi->qi_lru, sc);
 }
@@ -680,16 +678,18 @@ xfs_qm_init_quotainfo(
 	if (XFS_IS_PQUOTA_ON(mp))
 		xfs_qm_set_defquota(mp, XFS_DQTYPE_PROJ, qinf);
 
-	qinf->qi_shrinker.count_objects = xfs_qm_shrink_count;
-	qinf->qi_shrinker.scan_objects = xfs_qm_shrink_scan;
-	qinf->qi_shrinker.seeks = DEFAULT_SEEKS;
-	qinf->qi_shrinker.flags = SHRINKER_NUMA_AWARE;
-
-	error = register_shrinker(&qinf->qi_shrinker, "xfs-qm:%s",
-				  mp->m_super->s_id);
-	if (error)
+	qinf->qi_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE, "xfs-qm:%s",
+					   mp->m_super->s_id);
+	if (!qinf->qi_shrinker)
 		goto out_free_inos;
 
+	qinf->qi_shrinker->count_objects = xfs_qm_shrink_count;
+	qinf->qi_shrinker->scan_objects = xfs_qm_shrink_scan;
+	qinf->qi_shrinker->seeks = DEFAULT_SEEKS;
+	qinf->qi_shrinker->private_data = qinf;
+
+	shrinker_register(qinf->qi_shrinker);
+
 	return 0;
 
 out_free_inos:
@@ -718,7 +718,7 @@ xfs_qm_destroy_quotainfo(
 	qi = mp->m_quotainfo;
 	ASSERT(qi != NULL);
 
-	unregister_shrinker(&qi->qi_shrinker);
+	shrinker_unregister(qi->qi_shrinker);
 	list_lru_destroy(&qi->qi_lru);
 	xfs_qm_destroy_quotainos(qi);
 	mutex_destroy(&qi->qi_tree_lock);
diff --git a/fs/xfs/xfs_qm.h b/fs/xfs/xfs_qm.h
index 9683f0457d19..d5c9fc4ba591 100644
--- a/fs/xfs/xfs_qm.h
+++ b/fs/xfs/xfs_qm.h
@@ -63,7 +63,7 @@ struct xfs_quotainfo {
 	struct xfs_def_quota	qi_usr_default;
 	struct xfs_def_quota	qi_grp_default;
 	struct xfs_def_quota	qi_prj_default;
-	struct shrinker		qi_shrinker;
+	struct shrinker		*qi_shrinker;
 
 	/* Minimum and maximum quota expiration timestamp values. */
 	time64_t		qi_expiry_min;
-- 
2.30.2

[PATCH v2 39/47] zsmalloc: dynamically allocate the mm-zspool shrinker

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the mm-zspool shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct zs_pool.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/zsmalloc.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 32f5bc4074df..bbbffe313318 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -229,7 +229,7 @@ struct zs_pool {
 	struct zs_pool_stats stats;
 
 	/* Compact classes */
-	struct shrinker shrinker;
+	struct shrinker *shrinker;
 
 #ifdef CONFIG_ZSMALLOC_STAT
 	struct dentry *stat_dentry;
@@ -2082,8 +2082,7 @@ static unsigned long zs_shrinker_scan(struct shrinker *shrinker,
 		struct shrink_control *sc)
 {
 	unsigned long pages_freed;
-	struct zs_pool *pool = container_of(shrinker, struct zs_pool,
-			shrinker);
+	struct zs_pool *pool = shrinker->private_data;
 
 	/*
 	 * Compact classes and calculate compaction delta.
@@ -2101,8 +2100,7 @@ static unsigned long zs_shrinker_count(struct shrinker *shrinker,
 	int i;
 	struct size_class *class;
 	unsigned long pages_to_free = 0;
-	struct zs_pool *pool = container_of(shrinker, struct zs_pool,
-			shrinker);
+	struct zs_pool *pool = shrinker->private_data;
 
 	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
 		class = pool->size_class[i];
@@ -2117,18 +2115,24 @@ static unsigned long zs_shrinker_count(struct shrinker *shrinker,
 
 static void zs_unregister_shrinker(struct zs_pool *pool)
 {
-	unregister_shrinker(&pool->shrinker);
+	shrinker_unregister(pool->shrinker);
 }
 
 static int zs_register_shrinker(struct zs_pool *pool)
 {
-	pool->shrinker.scan_objects = zs_shrinker_scan;
-	pool->shrinker.count_objects = zs_shrinker_count;
-	pool->shrinker.batch = 0;
-	pool->shrinker.seeks = DEFAULT_SEEKS;
+	pool->shrinker = shrinker_alloc(0, "mm-zspool:%s", pool->name);
+	if (!pool->shrinker)
+		return -ENOMEM;
+
+	pool->shrinker->scan_objects = zs_shrinker_scan;
+	pool->shrinker->count_objects = zs_shrinker_count;
+	pool->shrinker->batch = 0;
+	pool->shrinker->seeks = DEFAULT_SEEKS;
+	pool->shrinker->private_data = pool;
 
-	return register_shrinker(&pool->shrinker, "mm-zspool:%s",
-				 pool->name);
+	shrinker_register(pool->shrinker);
+
+	return 0;
 }
 
 static int calculate_zspage_chain_size(int class_size)
-- 
2.30.2

[PATCH v2 40/47] fs: super: dynamically allocate the s_shrink

[Qi Zheng]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the s_shrink, so that it can be freed asynchronously
using kfree_rcu(). Then it doesn't need to wait for RCU read-side critical
section when releasing the struct super_block.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 fs/btrfs/super.c   |  2 +-
 fs/kernfs/mount.c  |  2 +-
 fs/proc/root.c     |  2 +-
 fs/super.c         | 37 +++++++++++++++++++++----------------
 include/linux/fs.h |  2 +-
 5 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f1dd172d8d5b..fad4ded26c80 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1513,7 +1513,7 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
 			error = -EBUSY;
 	} else {
 		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
-		shrinker_debugfs_rename(&s->s_shrink, "sb-%s:%s", fs_type->name,
+		shrinker_debugfs_rename(s->s_shrink, "sb-%s:%s", fs_type->name,
 					s->s_id);
 		btrfs_sb(s)->bdev_holder = fs_type;
 		error = btrfs_fill_super(s, fs_devices, data);
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index d49606accb07..2657ff1181f1 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -256,7 +256,7 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k
 	sb->s_time_gran = 1;
 
 	/* sysfs dentries and inodes don't require IO to create */
-	sb->s_shrink.seeks = 0;
+	sb->s_shrink->seeks = 0;
 
 	/* get root inode, initialize and unlock it */
 	down_read(&kf_root->kernfs_rwsem);
diff --git a/fs/proc/root.c b/fs/proc/root.c
index a86e65a608da..22b78b28b477 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -188,7 +188,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
 
 	/* procfs dentries and inodes don't require IO to create */
-	s->s_shrink.seeks = 0;
+	s->s_shrink->seeks = 0;
 
 	pde_get(&proc_root);
 	root_inode = proc_get_inode(s, &proc_root);
diff --git a/fs/super.c b/fs/super.c
index e781226e2880..04643fd80886 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -67,7 +67,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	long	dentries;
 	long	inodes;
 
-	sb = container_of(shrink, struct super_block, s_shrink);
+	sb = shrink->private_data;
 
 	/*
 	 * Deadlock avoidance.  We may hold various FS locks, and we don't want
@@ -120,7 +120,7 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 	struct super_block *sb;
 	long	total_objects = 0;
 
-	sb = container_of(shrink, struct super_block, s_shrink);
+	sb = shrink->private_data;
 
 	/*
 	 * We don't call trylock_super() here as it is a scalability bottleneck,
@@ -182,7 +182,8 @@ static void destroy_unused_super(struct super_block *s)
 	security_sb_free(s);
 	put_user_ns(s->s_user_ns);
 	kfree(s->s_subtype);
-	free_prealloced_shrinker(&s->s_shrink);
+	if (s->s_shrink)
+		shrinker_free_non_registered(s->s_shrink);
 	/* no delays needed */
 	destroy_super_work(&s->destroy_work);
 }
@@ -259,16 +260,20 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	s->s_time_min = TIME64_MIN;
 	s->s_time_max = TIME64_MAX;
 
-	s->s_shrink.seeks = DEFAULT_SEEKS;
-	s->s_shrink.scan_objects = super_cache_scan;
-	s->s_shrink.count_objects = super_cache_count;
-	s->s_shrink.batch = 1024;
-	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
-	if (prealloc_shrinker(&s->s_shrink, "sb-%s", type->name))
+	s->s_shrink = shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
+				     "sb-%s", type->name);
+	if (!s->s_shrink)
 		goto fail;
-	if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
+
+	s->s_shrink->seeks = DEFAULT_SEEKS;
+	s->s_shrink->scan_objects = super_cache_scan;
+	s->s_shrink->count_objects = super_cache_count;
+	s->s_shrink->batch = 1024;
+	s->s_shrink->private_data = s;
+
+	if (list_lru_init_memcg(&s->s_dentry_lru, s->s_shrink))
 		goto fail;
-	if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
+	if (list_lru_init_memcg(&s->s_inode_lru, s->s_shrink))
 		goto fail;
 	return s;
 
@@ -326,7 +331,7 @@ void deactivate_locked_super(struct super_block *s)
 {
 	struct file_system_type *fs = s->s_type;
 	if (atomic_dec_and_test(&s->s_active)) {
-		unregister_shrinker(&s->s_shrink);
+		shrinker_unregister(s->s_shrink);
 		fs->kill_sb(s);
 
 		/*
@@ -599,7 +604,7 @@ struct super_block *sget_fc(struct fs_context *fc,
 	hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
 	spin_unlock(&sb_lock);
 	get_filesystem(s->s_type);
-	register_shrinker_prepared(&s->s_shrink);
+	shrinker_register(s->s_shrink);
 	return s;
 
 share_extant_sb:
@@ -678,7 +683,7 @@ struct super_block *sget(struct file_system_type *type,
 	hlist_add_head(&s->s_instances, &type->fs_supers);
 	spin_unlock(&sb_lock);
 	get_filesystem(type);
-	register_shrinker_prepared(&s->s_shrink);
+	shrinker_register(s->s_shrink);
 	return s;
 }
 EXPORT_SYMBOL(sget);
@@ -1312,7 +1317,7 @@ int get_tree_bdev(struct fs_context *fc,
 		down_write(&s->s_umount);
 	} else {
 		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
-		shrinker_debugfs_rename(&s->s_shrink, "sb-%s:%s",
+		shrinker_debugfs_rename(s->s_shrink, "sb-%s:%s",
 					fc->fs_type->name, s->s_id);
 		sb_set_blocksize(s, block_size(bdev));
 		error = fill_super(s, fc);
@@ -1385,7 +1390,7 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
 		down_write(&s->s_umount);
 	} else {
 		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
-		shrinker_debugfs_rename(&s->s_shrink, "sb-%s:%s",
+		shrinker_debugfs_rename(s->s_shrink, "sb-%s:%s",
 					fs_type->name, s->s_id);
 		sb_set_blocksize(s, block_size(bdev));
 		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b4dca987a5d8..92748fc368b2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1231,7 +1231,7 @@ struct super_block {
 
 	const struct dentry_operations *s_d_op; /* default d_op for dentries */
 
-	struct shrinker s_shrink;	/* per-sb shrinker handle */
+	struct shrinker *s_shrink;	/* per-sb shrinker handle */
 
 	/* Number of inodes with nlink == 0 but still referenced */
 	atomic_long_t s_remove_count;
-- 
2.30.2

[PATCH v2 41/47] mm: shrinker: remove old APIs

[Qi Zheng]

Now no users are using the old APIs, just remove them.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 include/linux/shrinker.h |   7 --
 mm/shrinker.c            | 143 ---------------------------------------
 2 files changed, 150 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 296f5e163861..e464b4e9be0e 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -105,13 +105,6 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
 void shrinker_register(struct shrinker *shrinker);
 void shrinker_unregister(struct shrinker *shrinker);
 
-extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
-					    const char *fmt, ...);
-extern void register_shrinker_prepared(struct shrinker *shrinker);
-extern int __printf(2, 3) register_shrinker(struct shrinker *shrinker,
-					    const char *fmt, ...);
-extern void unregister_shrinker(struct shrinker *shrinker);
-extern void free_prealloced_shrinker(struct shrinker *shrinker);
 extern void synchronize_shrinkers(void);
 
 #ifdef CONFIG_SHRINKER_DEBUG
diff --git a/mm/shrinker.c b/mm/shrinker.c
index d820e4cc5806..2f3635ad1b45 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -661,149 +661,6 @@ void shrinker_unregister(struct shrinker *shrinker)
 }
 EXPORT_SYMBOL(shrinker_unregister);
 
-/*
- * Add a shrinker callback to be called from the vm.
- */
-static int __prealloc_shrinker(struct shrinker *shrinker)
-{
-	unsigned int size;
-	int err;
-
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
-		err = prealloc_memcg_shrinker(shrinker);
-		if (err != -ENOSYS)
-			return err;
-
-		shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
-	}
-
-	size = sizeof(*shrinker->nr_deferred);
-	if (shrinker->flags & SHRINKER_NUMA_AWARE)
-		size *= nr_node_ids;
-
-	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
-	if (!shrinker->nr_deferred)
-		return -ENOMEM;
-
-	return 0;
-}
-
-#ifdef CONFIG_SHRINKER_DEBUG
-int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	va_list ap;
-	int err;
-
-	va_start(ap, fmt);
-	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
-	va_end(ap);
-	if (!shrinker->name)
-		return -ENOMEM;
-
-	err = __prealloc_shrinker(shrinker);
-	if (err) {
-		kfree_const(shrinker->name);
-		shrinker->name = NULL;
-	}
-
-	return err;
-}
-#else
-int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	return __prealloc_shrinker(shrinker);
-}
-#endif
-
-void free_prealloced_shrinker(struct shrinker *shrinker)
-{
-#ifdef CONFIG_SHRINKER_DEBUG
-	kfree_const(shrinker->name);
-	shrinker->name = NULL;
-#endif
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
-		down_write(&shrinker_rwsem);
-		unregister_memcg_shrinker(shrinker);
-		up_write(&shrinker_rwsem);
-		return;
-	}
-
-	kfree(shrinker->nr_deferred);
-	shrinker->nr_deferred = NULL;
-}
-
-void register_shrinker_prepared(struct shrinker *shrinker)
-{
-	down_write(&shrinker_rwsem);
-	list_add_tail(&shrinker->list, &shrinker_list);
-	shrinker->flags |= SHRINKER_REGISTERED;
-	shrinker_debugfs_add(shrinker);
-	up_write(&shrinker_rwsem);
-}
-
-static int __register_shrinker(struct shrinker *shrinker)
-{
-	int err = __prealloc_shrinker(shrinker);
-
-	if (err)
-		return err;
-	register_shrinker_prepared(shrinker);
-	return 0;
-}
-
-#ifdef CONFIG_SHRINKER_DEBUG
-int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	va_list ap;
-	int err;
-
-	va_start(ap, fmt);
-	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
-	va_end(ap);
-	if (!shrinker->name)
-		return -ENOMEM;
-
-	err = __register_shrinker(shrinker);
-	if (err) {
-		kfree_const(shrinker->name);
-		shrinker->name = NULL;
-	}
-	return err;
-}
-#else
-int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
-{
-	return __register_shrinker(shrinker);
-}
-#endif
-EXPORT_SYMBOL(register_shrinker);
-
-/*
- * Remove one
- */
-void unregister_shrinker(struct shrinker *shrinker)
-{
-	struct dentry *debugfs_entry;
-	int debugfs_id;
-
-	if (!(shrinker->flags & SHRINKER_REGISTERED))
-		return;
-
-	down_write(&shrinker_rwsem);
-	list_del(&shrinker->list);
-	shrinker->flags &= ~SHRINKER_REGISTERED;
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		unregister_memcg_shrinker(shrinker);
-	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
-	up_write(&shrinker_rwsem);
-
-	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
-
-	kfree(shrinker->nr_deferred);
-	shrinker->nr_deferred = NULL;
-}
-EXPORT_SYMBOL(unregister_shrinker);
-
 /**
  * synchronize_shrinkers - Wait for all running shrinkers to complete.
  *
-- 
2.30.2

[PATCH v2 42/47] drm/ttm: introduce pool_shrink_rwsem

[Qi Zheng]

Currently, the synchronize_shrinkers() is only used by TTM pool. It only
requires that no shrinkers run in parallel.

After we use RCU+refcount method to implement the lockless slab shrink,
we can not use shrinker_rwsem or synchronize_rcu() to guarantee that all
shrinker invocations have seen an update before freeing memory.

So we introduce a new pool_shrink_rwsem to implement a private
synchronize_shrinkers(), so as to achieve the same purpose.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/gpu/drm/ttm/ttm_pool.c | 15 +++++++++++++++
 include/linux/shrinker.h       |  2 --
 mm/shrinker.c                  | 15 ---------------
 3 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index e1eb73d0b72a..8a35fd48ec46 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -74,6 +74,7 @@ static struct ttm_pool_type global_dma32_uncached[MAX_ORDER + 1];
 static spinlock_t shrinker_lock;
 static struct list_head shrinker_list;
 static struct shrinker *mm_shrinker;
+static DECLARE_RWSEM(pool_shrink_rwsem);
 
 /* Allocate pages of size 1 << order with the given gfp_flags */
 static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags,
@@ -317,6 +318,7 @@ static unsigned int ttm_pool_shrink(void)
 	unsigned int num_pages;
 	struct page *p;
 
+	down_read(&pool_shrink_rwsem);
 	spin_lock(&shrinker_lock);
 	pt = list_first_entry(&shrinker_list, typeof(*pt), shrinker_list);
 	list_move_tail(&pt->shrinker_list, &shrinker_list);
@@ -329,6 +331,7 @@ static unsigned int ttm_pool_shrink(void)
 	} else {
 		num_pages = 0;
 	}
+	up_read(&pool_shrink_rwsem);
 
 	return num_pages;
 }
@@ -572,6 +575,18 @@ void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
 }
 EXPORT_SYMBOL(ttm_pool_init);
 
+/**
+ * synchronize_shrinkers - Wait for all running shrinkers to complete.
+ *
+ * This is useful to guarantee that all shrinker invocations have seen an
+ * update, before freeing memory, similar to rcu.
+ */
+static void synchronize_shrinkers(void)
+{
+	down_write(&pool_shrink_rwsem);
+	up_write(&pool_shrink_rwsem);
+}
+
 /**
  * ttm_pool_fini - Cleanup a pool
  *
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index e464b4e9be0e..23ea9360c5d8 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -105,8 +105,6 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
 void shrinker_register(struct shrinker *shrinker);
 void shrinker_unregister(struct shrinker *shrinker);
 
-extern void synchronize_shrinkers(void);
-
 #ifdef CONFIG_SHRINKER_DEBUG
 extern int shrinker_debugfs_add(struct shrinker *shrinker);
 extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 2f3635ad1b45..3c4d3fe2fa17 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -660,18 +660,3 @@ void shrinker_unregister(struct shrinker *shrinker)
 	kfree(shrinker);
 }
 EXPORT_SYMBOL(shrinker_unregister);
-
-/**
- * synchronize_shrinkers - Wait for all running shrinkers to complete.
- *
- * This is equivalent to calling unregister_shrink() and register_shrinker(),
- * but atomically and with less overhead. This is useful to guarantee that all
- * shrinker invocations have seen an update, before freeing memory, similar to
- * rcu.
- */
-void synchronize_shrinkers(void)
-{
-	down_write(&shrinker_rwsem);
-	up_write(&shrinker_rwsem);
-}
-EXPORT_SYMBOL(synchronize_shrinkers);
-- 
2.30.2

[PATCH v2 43/47] mm: shrinker: add a secondary array for shrinker_info::{map, nr_deferred}

[Qi Zheng]

Currently, we maintain two linear arrays per node per memcg, which are
shrinker_info::map and shrinker_info::nr_deferred. And we need to resize
them when the shrinker_nr_max is exceeded, that is, allocate a new array,
and then copy the old array to the new array, and finally free the old
array by RCU.

For shrinker_info::map, we do set_bit() under the RCU lock, so we may set
the value into the old map which is about to be freed. This may cause the
value set to be lost. The current solution is not to copy the old map when
resizing, but to set all the corresponding bits in the new map to 1. This
solves the data loss problem, but bring the overhead of more pointless
loops while doing memcg slab shrink.

For shrinker_info::nr_deferred, we will only modify it under the read lock
of shrinker_rwsem, so it will not run concurrently with the resizing. But
after we make memcg slab shrink lockless, there will be the same data loss
problem as shrinker_info::map, and we can't work around it like the map.

For such resizable arrays, the most straightforward idea is to change it
to xarray, like we did for list_lru [1]. We need to do xa_store() in the
list_lru_add()-->set_shrinker_bit(), but this will cause memory
allocation, and the list_lru_add() doesn't accept failure. A possible
solution is to pre-allocate, but the location of pre-allocation is not
well determined.

Therefore, this commit chooses to introduce a secondary array for
shrinker_info::{map, nr_deferred}, so that we only need to copy this
secondary array every time the size is resized. Then even if we get the
old secondary array under the RCU lock, the found map and nr_deferred are
also true, so no data is lost.

[1]. https://lore.kernel.org/all/20220228122126.37293-13-songmuchun@bytedance.com/

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 include/linux/memcontrol.h |  12 +-
 include/linux/shrinker.h   |  17 +++
 mm/shrinker.c              | 250 +++++++++++++++++++++++--------------
 3 files changed, 172 insertions(+), 107 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 58eb7ca65699..1a2e9d15822d 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -21,6 +21,7 @@
 #include <linux/vmstat.h>
 #include <linux/writeback.h>
 #include <linux/page-flags.h>
+#include <linux/shrinker.h>
 
 struct mem_cgroup;
 struct obj_cgroup;
@@ -88,17 +89,6 @@ struct mem_cgroup_reclaim_iter {
 	unsigned int generation;
 };
 
-/*
- * Bitmap and deferred work of shrinker::id corresponding to memcg-aware
- * shrinkers, which have elements charged to this memcg.
- */
-struct shrinker_info {
-	struct rcu_head rcu;
-	atomic_long_t *nr_deferred;
-	unsigned long *map;
-	int map_nr_max;
-};
-
 struct lruvec_stats_percpu {
 	/* Local (CPU and cgroup) state */
 	long state[NR_VM_NODE_STAT_ITEMS];
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 23ea9360c5d8..36977a70bebb 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -5,6 +5,23 @@
 #include <linux/atomic.h>
 #include <linux/types.h>
 
+#define SHRINKER_UNIT_BITS	BITS_PER_LONG
+
+/*
+ * Bitmap and deferred work of shrinker::id corresponding to memcg-aware
+ * shrinkers, which have elements charged to the memcg.
+ */
+struct shrinker_info_unit {
+	atomic_long_t nr_deferred[SHRINKER_UNIT_BITS];
+	DECLARE_BITMAP(map, SHRINKER_UNIT_BITS);
+};
+
+struct shrinker_info {
+	struct rcu_head rcu;
+	int map_nr_max;
+	struct shrinker_info_unit *unit[];
+};
+
 /*
  * This struct is used to pass information from page reclaim to the shrinkers.
  * We consolidate the values for easier extension later.
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 3c4d3fe2fa17..8a1fe844f1a4 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -10,15 +10,50 @@ DECLARE_RWSEM(shrinker_rwsem);
 #ifdef CONFIG_MEMCG
 static int shrinker_nr_max;
 
-/* The shrinker_info is expanded in a batch of BITS_PER_LONG */
-static inline int shrinker_map_size(int nr_items)
+static inline int shrinker_unit_size(int nr_items)
 {
-	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
+	return (DIV_ROUND_UP(nr_items, SHRINKER_UNIT_BITS) * sizeof(struct shrinker_info_unit *));
 }
 
-static inline int shrinker_defer_size(int nr_items)
+static inline void shrinker_unit_free(struct shrinker_info *info, int start)
 {
-	return (round_up(nr_items, BITS_PER_LONG) * sizeof(atomic_long_t));
+	struct shrinker_info_unit **unit;
+	int nr, i;
+
+	if (!info)
+		return;
+
+	unit = info->unit;
+	nr = DIV_ROUND_UP(info->map_nr_max, SHRINKER_UNIT_BITS);
+
+	for (i = start; i < nr; i++) {
+		if (!unit[i])
+			break;
+
+		kvfree(unit[i]);
+		unit[i] = NULL;
+	}
+}
+
+static inline int shrinker_unit_alloc(struct shrinker_info *new,
+				       struct shrinker_info *old, int nid)
+{
+	struct shrinker_info_unit *unit;
+	int nr = DIV_ROUND_UP(new->map_nr_max, SHRINKER_UNIT_BITS);
+	int start = old ? DIV_ROUND_UP(old->map_nr_max, SHRINKER_UNIT_BITS) : 0;
+	int i;
+
+	for (i = start; i < nr; i++) {
+		unit = kvzalloc_node(sizeof(*unit), GFP_KERNEL, nid);
+		if (!unit) {
+			shrinker_unit_free(new, start);
+			return -ENOMEM;
+		}
+
+		new->unit[i] = unit;
+	}
+
+	return 0;
 }
 
 void free_shrinker_info(struct mem_cgroup *memcg)
@@ -30,6 +65,7 @@ void free_shrinker_info(struct mem_cgroup *memcg)
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
 		info = rcu_dereference_protected(pn->shrinker_info, true);
+		shrinker_unit_free(info, 0);
 		kvfree(info);
 		rcu_assign_pointer(pn->shrinker_info, NULL);
 	}
@@ -38,28 +74,27 @@ void free_shrinker_info(struct mem_cgroup *memcg)
 int alloc_shrinker_info(struct mem_cgroup *memcg)
 {
 	struct shrinker_info *info;
-	int nid, size, ret = 0;
-	int map_size, defer_size = 0;
+	int nid, ret = 0;
+	int array_size = 0;
 
 	down_write(&shrinker_rwsem);
-	map_size = shrinker_map_size(shrinker_nr_max);
-	defer_size = shrinker_defer_size(shrinker_nr_max);
-	size = map_size + defer_size;
+	array_size = shrinker_unit_size(shrinker_nr_max);
 	for_each_node(nid) {
-		info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid);
-		if (!info) {
-			free_shrinker_info(memcg);
-			ret = -ENOMEM;
-			break;
-		}
-		info->nr_deferred = (atomic_long_t *)(info + 1);
-		info->map = (void *)info->nr_deferred + defer_size;
+		info = kvzalloc_node(sizeof(*info) + array_size, GFP_KERNEL, nid);
+		if (!info)
+			goto err;
 		info->map_nr_max = shrinker_nr_max;
+		if (shrinker_unit_alloc(info, NULL, nid))
+			goto err;
 		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
 	}
 	up_write(&shrinker_rwsem);
 
 	return ret;
+
+err:
+	free_shrinker_info(memcg);
+	return -ENOMEM;
 }
 
 static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
@@ -69,15 +104,12 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
 					 lockdep_is_held(&shrinker_rwsem));
 }
 
-static int expand_one_shrinker_info(struct mem_cgroup *memcg,
-				    int map_size, int defer_size,
-				    int old_map_size, int old_defer_size,
-				    int new_nr_max)
+static int expand_one_shrinker_info(struct mem_cgroup *memcg, int new_size,
+				    int old_size, int new_nr_max)
 {
 	struct shrinker_info *new, *old;
 	struct mem_cgroup_per_node *pn;
 	int nid;
-	int size = map_size + defer_size;
 
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
@@ -90,21 +122,18 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
 		if (new_nr_max <= old->map_nr_max)
 			continue;
 
-		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
+		new = kvmalloc_node(sizeof(*new) + new_size, GFP_KERNEL, nid);
 		if (!new)
 			return -ENOMEM;
 
-		new->nr_deferred = (atomic_long_t *)(new + 1);
-		new->map = (void *)new->nr_deferred + defer_size;
 		new->map_nr_max = new_nr_max;
 
-		/* map: set all old bits, clear all new bits */
-		memset(new->map, (int)0xff, old_map_size);
-		memset((void *)new->map + old_map_size, 0, map_size - old_map_size);
-		/* nr_deferred: copy old values, clear all new values */
-		memcpy(new->nr_deferred, old->nr_deferred, old_defer_size);
-		memset((void *)new->nr_deferred + old_defer_size, 0,
-		       defer_size - old_defer_size);
+		/* copy old values, allocate all new values */
+		memcpy(new->unit, old->unit, old_size);
+		if (shrinker_unit_alloc(new, old, nid)) {
+			kvfree(new);
+			return -ENOMEM;
+		}
 
 		rcu_assign_pointer(pn->shrinker_info, new);
 		kvfree_rcu(old, rcu);
@@ -116,9 +145,8 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
 static int expand_shrinker_info(int new_id)
 {
 	int ret = 0;
-	int new_nr_max = round_up(new_id + 1, BITS_PER_LONG);
-	int map_size, defer_size = 0;
-	int old_map_size, old_defer_size = 0;
+	int new_nr_max = round_up(new_id + 1, SHRINKER_UNIT_BITS);
+	int new_size, old_size = 0;
 	struct mem_cgroup *memcg;
 
 	if (!root_mem_cgroup)
@@ -126,15 +154,12 @@ static int expand_shrinker_info(int new_id)
 
 	lockdep_assert_held(&shrinker_rwsem);
 
-	map_size = shrinker_map_size(new_nr_max);
-	defer_size = shrinker_defer_size(new_nr_max);
-	old_map_size = shrinker_map_size(shrinker_nr_max);
-	old_defer_size = shrinker_defer_size(shrinker_nr_max);
+	new_size = shrinker_unit_size(new_nr_max);
+	old_size = shrinker_unit_size(shrinker_nr_max);
 
 	memcg = mem_cgroup_iter(NULL, NULL, NULL);
 	do {
-		ret = expand_one_shrinker_info(memcg, map_size, defer_size,
-					       old_map_size, old_defer_size,
+		ret = expand_one_shrinker_info(memcg, new_size, old_size,
 					       new_nr_max);
 		if (ret) {
 			mem_cgroup_iter_break(NULL, memcg);
@@ -148,17 +173,34 @@ static int expand_shrinker_info(int new_id)
 	return ret;
 }
 
+static inline int shriner_id_to_index(int shrinker_id)
+{
+	return shrinker_id / SHRINKER_UNIT_BITS;
+}
+
+static inline int shriner_id_to_offset(int shrinker_id)
+{
+	return shrinker_id % SHRINKER_UNIT_BITS;
+}
+
+static inline int calc_shrinker_id(int index, int offset)
+{
+	return index * SHRINKER_UNIT_BITS + offset;
+}
+
 void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 {
 	if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
 		struct shrinker_info *info;
+		struct shrinker_info_unit *unit;
 
 		rcu_read_lock();
 		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+		unit = info->unit[shriner_id_to_index(shrinker_id)];
 		if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
 			/* Pairs with smp mb in shrink_slab() */
 			smp_mb__before_atomic();
-			set_bit(shrinker_id, info->map);
+			set_bit(shriner_id_to_offset(shrinker_id), unit->map);
 		}
 		rcu_read_unlock();
 	}
@@ -207,26 +249,31 @@ static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
 				   struct mem_cgroup *memcg)
 {
 	struct shrinker_info *info;
+	struct shrinker_info_unit *unit;
 
 	info = shrinker_info_protected(memcg, nid);
-	return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
+	unit = info->unit[shriner_id_to_index(shrinker->id)];
+	return atomic_long_xchg(&unit->nr_deferred[shriner_id_to_offset(shrinker->id)], 0);
 }
 
 static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
 				  struct mem_cgroup *memcg)
 {
 	struct shrinker_info *info;
+	struct shrinker_info_unit *unit;
 
 	info = shrinker_info_protected(memcg, nid);
-	return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
+	unit = info->unit[shriner_id_to_index(shrinker->id)];
+	return atomic_long_add_return(nr, &unit->nr_deferred[shriner_id_to_offset(shrinker->id)]);
 }
 
 void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 {
-	int i, nid;
+	int nid, index, offset;
 	long nr;
 	struct mem_cgroup *parent;
 	struct shrinker_info *child_info, *parent_info;
+	struct shrinker_info_unit *child_unit, *parent_unit;
 
 	parent = parent_mem_cgroup(memcg);
 	if (!parent)
@@ -237,9 +284,13 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 	for_each_node(nid) {
 		child_info = shrinker_info_protected(memcg, nid);
 		parent_info = shrinker_info_protected(parent, nid);
-		for (i = 0; i < child_info->map_nr_max; i++) {
-			nr = atomic_long_read(&child_info->nr_deferred[i]);
-			atomic_long_add(nr, &parent_info->nr_deferred[i]);
+		for (index = 0; index < shriner_id_to_index(child_info->map_nr_max); index++) {
+			child_unit = child_info->unit[index];
+			parent_unit = parent_info->unit[index];
+			for (offset = 0; offset < SHRINKER_UNIT_BITS; offset++) {
+				nr = atomic_long_read(&child_unit->nr_deferred[offset]);
+				atomic_long_add(nr, &parent_unit->nr_deferred[offset]);
+			}
 		}
 	}
 	up_read(&shrinker_rwsem);
@@ -405,7 +456,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 {
 	struct shrinker_info *info;
 	unsigned long ret, freed = 0;
-	int i;
+	int offset, index = 0;
 
 	if (!mem_cgroup_online(memcg))
 		return 0;
@@ -417,56 +468,63 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 	if (unlikely(!info))
 		goto unlock;
 
-	for_each_set_bit(i, info->map, info->map_nr_max) {
-		struct shrink_control sc = {
-			.gfp_mask = gfp_mask,
-			.nid = nid,
-			.memcg = memcg,
-		};
-		struct shrinker *shrinker;
+	for (; index < shriner_id_to_index(info->map_nr_max); index++) {
+		struct shrinker_info_unit *unit;
 
-		shrinker = idr_find(&shrinker_idr, i);
-		if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
-			if (!shrinker)
-				clear_bit(i, info->map);
-			continue;
-		}
+		unit = info->unit[index];
 
-		/* Call non-slab shrinkers even though kmem is disabled */
-		if (!memcg_kmem_online() &&
-		    !(shrinker->flags & SHRINKER_NONSLAB))
-			continue;
+		for_each_set_bit(offset, unit->map, SHRINKER_UNIT_BITS) {
+			struct shrink_control sc = {
+				.gfp_mask = gfp_mask,
+				.nid = nid,
+				.memcg = memcg,
+			};
+			struct shrinker *shrinker;
+			int shrinker_id = calc_shrinker_id(index, offset);
 
-		ret = do_shrink_slab(&sc, shrinker, priority);
-		if (ret == SHRINK_EMPTY) {
-			clear_bit(i, info->map);
-			/*
-			 * After the shrinker reported that it had no objects to
-			 * free, but before we cleared the corresponding bit in
-			 * the memcg shrinker map, a new object might have been
-			 * added. To make sure, we have the bit set in this
-			 * case, we invoke the shrinker one more time and reset
-			 * the bit if it reports that it is not empty anymore.
-			 * The memory barrier here pairs with the barrier in
-			 * set_shrinker_bit():
-			 *
-			 * list_lru_add()     shrink_slab_memcg()
-			 *   list_add_tail()    clear_bit()
-			 *   <MB>               <MB>
-			 *   set_bit()          do_shrink_slab()
-			 */
-			smp_mb__after_atomic();
-			ret = do_shrink_slab(&sc, shrinker, priority);
-			if (ret == SHRINK_EMPTY)
-				ret = 0;
-			else
-				set_shrinker_bit(memcg, nid, i);
-		}
-		freed += ret;
+			shrinker = idr_find(&shrinker_idr, shrinker_id);
+			if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
+				if (!shrinker)
+					clear_bit(offset, unit->map);
+				continue;
+			}
 
-		if (rwsem_is_contended(&shrinker_rwsem)) {
-			freed = freed ? : 1;
-			break;
+			/* Call non-slab shrinkers even though kmem is disabled */
+			if (!memcg_kmem_online() &&
+			    !(shrinker->flags & SHRINKER_NONSLAB))
+				continue;
+
+			ret = do_shrink_slab(&sc, shrinker, priority);
+			if (ret == SHRINK_EMPTY) {
+				clear_bit(offset, unit->map);
+				/*
+				 * After the shrinker reported that it had no objects to
+				 * free, but before we cleared the corresponding bit in
+				 * the memcg shrinker map, a new object might have been
+				 * added. To make sure, we have the bit set in this
+				 * case, we invoke the shrinker one more time and reset
+				 * the bit if it reports that it is not empty anymore.
+				 * The memory barrier here pairs with the barrier in
+				 * set_shrinker_bit():
+				 *
+				 * list_lru_add()     shrink_slab_memcg()
+				 *   list_add_tail()    clear_bit()
+				 *   <MB>               <MB>
+				 *   set_bit()          do_shrink_slab()
+				 */
+				smp_mb__after_atomic();
+				ret = do_shrink_slab(&sc, shrinker, priority);
+				if (ret == SHRINK_EMPTY)
+					ret = 0;
+				else
+					set_shrinker_bit(memcg, nid, shrinker_id);
+			}
+			freed += ret;
+
+			if (rwsem_is_contended(&shrinker_rwsem)) {
+				freed = freed ? : 1;
+				goto unlock;
+			}
 		}
 	}
 unlock:
-- 
2.30.2

[PATCH v2 44/47] mm: shrinker: make global slab shrink lockless

[Qi Zheng]

The shrinker_rwsem is a global read-write lock in shrinkers subsystem,
which protects most operations such as slab shrink, registration and
unregistration of shrinkers, etc. This can easily cause problems in the
following cases.

1) When the memory pressure is high and there are many filesystems
   mounted or unmounted at the same time, slab shrink will be affected
   (down_read_trylock() failed).

   Such as the real workload mentioned by Kirill Tkhai:

   ```
   One of the real workloads from my experience is start
   of an overcommitted node containing many starting
   containers after node crash (or many resuming containers
   after reboot for kernel update). In these cases memory
   pressure is huge, and the node goes round in long reclaim.
   ```

2) If a shrinker is blocked (such as the case mentioned
   in [1]) and a writer comes in (such as mount a fs),
   then this writer will be blocked and cause all
   subsequent shrinker-related operations to be blocked.

Even if there is no competitor when shrinking slab, there may still be a
problem. The down_read_trylock() may become a perf hotspot with frequent
calls to shrink_slab(). Because of the poor multicore scalability of
atomic operations, this can lead to a significant drop in IPC
(instructions per cycle).

We used to implement the lockless slab shrink with SRCU [2], but then
kernel test robot reported -88.8% regression in
stress-ng.ramfs.ops_per_sec test case [3], so we reverted it [4].

This commit uses the refcount+RCU method [5] proposed by Dave Chinner
to re-implement the lockless global slab shrink. The memcg slab shrink is
handled in the subsequent patch.

For now, all shrinker instances are converted to dynamically allocated and
will be freed by kfree_rcu(). So we can use rcu_read_{lock,unlock}() to
ensure that the shrinker instance is valid.

And the shrinker instance will not be run again after unregistration. So
the structure that records the pointer of shrinker instance can be safely
freed without waiting for the RCU read-side critical section.

In this way, while we implement the lockless slab shrink, we don't need to
be blocked in unregister_shrinker().

The following are the test results:

stress-ng --timeout 60 --times --verify --metrics-brief --ramfs 9 &

1) Before applying this patchset:

setting to a 60 second run per stressor
dispatching hogs: 9 ramfs
stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
                          (secs)    (secs)    (secs)   (real time) (usr+sys time)
ramfs            735238     60.00     12.37    363.70     12253.05        1955.08
for a 60.01s run time:
   1440.27s available CPU time
     12.36s user time   (  0.86%)
    363.70s system time ( 25.25%)
    376.06s total time  ( 26.11%)
load average: 10.79 4.47 1.69
passed: 9: ramfs (9)
failed: 0
skipped: 0
successful run completed in 60.01s (1 min, 0.01 secs)

2) After applying this patchset:

setting to a 60 second run per stressor
dispatching hogs: 9 ramfs
stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
                          (secs)    (secs)    (secs)   (real time) (usr+sys time)
ramfs            746677     60.00     12.22    367.75     12443.70        1965.13
for a 60.01s run time:
   1440.26s available CPU time
     12.21s user time   (  0.85%)
    367.75s system time ( 25.53%)
    379.96s total time  ( 26.38%)
load average: 8.37 2.48 0.86
passed: 9: ramfs (9)
failed: 0
skipped: 0
successful run completed in 60.01s (1 min, 0.01 secs)

We can see that the ops/s has hardly changed.

[1]. https://lore.kernel.org/lkml/20191129214541.3110-1-ptikhomirov@virtuozzo.com/
[2]. https://lore.kernel.org/lkml/20230313112819.38938-1-zhengqi.arch@bytedance.com/
[3]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/
[4]. https://lore.kernel.org/all/20230609081518.3039120-1-qi.zheng@linux.dev/
[5]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 include/linux/shrinker.h | 19 +++++++---
 mm/shrinker.c            | 75 ++++++++++++++++++++++++++--------------
 mm/shrinker_debug.c      | 52 +++++++++++++++++++++-------
 3 files changed, 104 insertions(+), 42 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 36977a70bebb..335da93cccee 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -4,6 +4,7 @@
 
 #include <linux/atomic.h>
 #include <linux/types.h>
+#include <linux/refcount.h>
 
 #define SHRINKER_UNIT_BITS	BITS_PER_LONG
 
@@ -86,6 +87,10 @@ struct shrinker {
 	long batch;	/* reclaim batch size, 0 = default */
 	int seeks;	/* seeks to recreate an obj */
 	unsigned flags;
+	bool registered;
+
+	refcount_t refcount;
+	struct rcu_head rcu;
 
 	void *private_data;
 
@@ -106,14 +111,13 @@ struct shrinker {
 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
 
 /* Flags */
-#define SHRINKER_REGISTERED	(1 << 0)
-#define SHRINKER_NUMA_AWARE	(1 << 1)
-#define SHRINKER_MEMCG_AWARE	(1 << 2)
+#define SHRINKER_NUMA_AWARE	(1 << 0)
+#define SHRINKER_MEMCG_AWARE	(1 << 1)
 /*
  * It just makes sense when the shrinker is also MEMCG_AWARE for now,
  * non-MEMCG_AWARE shrinker should not have this flag set.
  */
-#define SHRINKER_NONSLAB	(1 << 3)
+#define SHRINKER_NONSLAB	(1 << 2)
 
 unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
 			  int priority);
@@ -122,6 +126,13 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
 void shrinker_register(struct shrinker *shrinker);
 void shrinker_unregister(struct shrinker *shrinker);
 
+static inline bool shrinker_try_get(struct shrinker *shrinker)
+{
+	return READ_ONCE(shrinker->registered) &&
+	       refcount_inc_not_zero(&shrinker->refcount);
+}
+void shrinker_put(struct shrinker *shrinker);
+
 #ifdef CONFIG_SHRINKER_DEBUG
 extern int shrinker_debugfs_add(struct shrinker *shrinker);
 extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 8a1fe844f1a4..8e3334749552 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -2,10 +2,13 @@
 #include <linux/memcontrol.h>
 #include <linux/rwsem.h>
 #include <linux/shrinker.h>
+#include <linux/rculist.h>
+#include <linux/spinlock.h>
 #include <trace/events/vmscan.h>
 
 LIST_HEAD(shrinker_list);
 DECLARE_RWSEM(shrinker_rwsem);
+DEFINE_SPINLOCK(shrinker_lock);
 
 #ifdef CONFIG_MEMCG
 static int shrinker_nr_max;
@@ -450,6 +453,18 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	return freed;
 }
 
+void shrinker_put(struct shrinker *shrinker)
+{
+	if (refcount_dec_and_test(&shrinker->refcount)) {
+		spin_lock(&shrinker_lock);
+		list_del_rcu(&shrinker->list);
+		spin_unlock(&shrinker_lock);
+
+		kfree(shrinker->nr_deferred);
+		kfree_rcu(shrinker, rcu);
+	}
+}
+
 #ifdef CONFIG_MEMCG
 static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			struct mem_cgroup *memcg, int priority)
@@ -483,7 +498,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			int shrinker_id = calc_shrinker_id(index, offset);
 
 			shrinker = idr_find(&shrinker_idr, shrinker_id);
-			if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
+			if (unlikely(!shrinker ||
+				     !READ_ONCE(shrinker->registered))) {
 				if (!shrinker)
 					clear_bit(offset, unit->map);
 				continue;
@@ -575,33 +591,42 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
 	if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
 		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
 
-	if (!down_read_trylock(&shrinker_rwsem))
-		goto out;
-
-	list_for_each_entry(shrinker, &shrinker_list, list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
 		struct shrink_control sc = {
 			.gfp_mask = gfp_mask,
 			.nid = nid,
 			.memcg = memcg,
 		};
 
+		if (!shrinker_try_get(shrinker))
+			continue;
+
+		/*
+		 * We can safely unlock the RCU lock here since we already
+		 * hold the refcount of the shrinker.
+		 */
+		rcu_read_unlock();
+
 		ret = do_shrink_slab(&sc, shrinker, priority);
 		if (ret == SHRINK_EMPTY)
 			ret = 0;
 		freed += ret;
+
 		/*
-		 * Bail out if someone want to register a new shrinker to
-		 * prevent the registration from being stalled for long periods
-		 * by parallel ongoing shrinking.
+		 * This shrinker may be deleted from shrinker_list and freed in
+		 * the shrinker_put() below, but this shrinker is still used for
+		 * the next traversal. So it is necessary to hold the RCU lock
+		 * first to prevent this shrinker from being freed, which also
+		 * ensures that the next shrinker that is traversed will not be
+		 * freed (even if it is deleted from shrinker_list at the same
+		 * time).
 		 */
-		if (rwsem_is_contended(&shrinker_rwsem)) {
-			freed = freed ? : 1;
-			break;
-		}
+		rcu_read_lock();
+		shrinker_put(shrinker);
 	}
 
-	up_read(&shrinker_rwsem);
-out:
+	rcu_read_unlock();
 	cond_resched();
 	return freed;
 }
@@ -686,11 +711,14 @@ EXPORT_SYMBOL(shrinker_free_non_registered);
 
 void shrinker_register(struct shrinker *shrinker)
 {
-	down_write(&shrinker_rwsem);
-	list_add_tail(&shrinker->list, &shrinker_list);
-	shrinker->flags |= SHRINKER_REGISTERED;
+	refcount_set(&shrinker->refcount, 1);
+
+	spin_lock(&shrinker_lock);
+	list_add_tail_rcu(&shrinker->list, &shrinker_list);
+	spin_unlock(&shrinker_lock);
+
 	shrinker_debugfs_add(shrinker);
-	up_write(&shrinker_rwsem);
+	WRITE_ONCE(shrinker->registered, true);
 }
 EXPORT_SYMBOL(shrinker_register);
 
@@ -699,12 +727,12 @@ void shrinker_unregister(struct shrinker *shrinker)
 	struct dentry *debugfs_entry;
 	int debugfs_id;
 
-	if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))
+	if (!shrinker || !READ_ONCE(shrinker->registered))
 		return;
 
+	WRITE_ONCE(shrinker->registered, false);
+
 	down_write(&shrinker_rwsem);
-	list_del(&shrinker->list);
-	shrinker->flags &= ~SHRINKER_REGISTERED;
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
 		unregister_memcg_shrinker(shrinker);
 	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
@@ -712,9 +740,6 @@ void shrinker_unregister(struct shrinker *shrinker)
 
 	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
 
-	kfree(shrinker->nr_deferred);
-	shrinker->nr_deferred = NULL;
-
-	kfree(shrinker);
+	shrinker_put(shrinker);
 }
 EXPORT_SYMBOL(shrinker_unregister);
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index f1becfd45853..c5573066adbf 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -5,6 +5,7 @@
 #include <linux/seq_file.h>
 #include <linux/shrinker.h>
 #include <linux/memcontrol.h>
+#include <linux/rculist.h>
 
 /* defined in vmscan.c */
 extern struct rw_semaphore shrinker_rwsem;
@@ -161,17 +162,21 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
 {
 	struct dentry *entry;
 	char buf[128];
-	int id;
-
-	lockdep_assert_held(&shrinker_rwsem);
+	int id, ret = 0;
 
 	/* debugfs isn't initialized yet, add debugfs entries later. */
 	if (!shrinker_debugfs_root)
 		return 0;
 
+	down_write(&shrinker_rwsem);
+	if (shrinker->debugfs_entry)
+		goto fail;
+
 	id = ida_alloc(&shrinker_debugfs_ida, GFP_KERNEL);
-	if (id < 0)
-		return id;
+	if (id < 0) {
+		ret = id;
+		goto fail;
+	}
 	shrinker->debugfs_id = id;
 
 	snprintf(buf, sizeof(buf), "%s-%d", shrinker->name, id);
@@ -180,7 +185,8 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
 	entry = debugfs_create_dir(buf, shrinker_debugfs_root);
 	if (IS_ERR(entry)) {
 		ida_free(&shrinker_debugfs_ida, id);
-		return PTR_ERR(entry);
+		ret = PTR_ERR(entry);
+		goto fail;
 	}
 	shrinker->debugfs_entry = entry;
 
@@ -188,7 +194,10 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
 			    &shrinker_debugfs_count_fops);
 	debugfs_create_file("scan", 0220, entry, shrinker,
 			    &shrinker_debugfs_scan_fops);
-	return 0;
+
+fail:
+	up_write(&shrinker_rwsem);
+	return ret;
 }
 
 int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
@@ -243,6 +252,11 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
 	shrinker->name = NULL;
 
 	*debugfs_id = entry ? shrinker->debugfs_id : -1;
+	/*
+	 * Ensure that shrinker->registered has been set to false before
+	 * shrinker->debugfs_entry is set to NULL.
+	 */
+	smp_wmb();
 	shrinker->debugfs_entry = NULL;
 
 	return entry;
@@ -266,14 +280,26 @@ static int __init shrinker_debugfs_init(void)
 	shrinker_debugfs_root = dentry;
 
 	/* Create debugfs entries for shrinkers registered at boot */
-	down_write(&shrinker_rwsem);
-	list_for_each_entry(shrinker, &shrinker_list, list)
+	rcu_read_lock();
+	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
+		if (!shrinker_try_get(shrinker))
+			continue;
+		rcu_read_unlock();
+
 		if (!shrinker->debugfs_entry) {
-			ret = shrinker_debugfs_add(shrinker);
-			if (ret)
-				break;
+			/* Paired with smp_wmb() in shrinker_debugfs_detach() */
+			smp_rmb();
+			if (READ_ONCE(shrinker->registered))
+				ret = shrinker_debugfs_add(shrinker);
 		}
-	up_write(&shrinker_rwsem);
+
+		rcu_read_lock();
+		shrinker_put(shrinker);
+
+		if (ret)
+			break;
+	}
+	rcu_read_unlock();
 
 	return ret;
 }
-- 
2.30.2

[PATCH v2 45/47] mm: shrinker: make memcg slab shrink lockless

[Qi Zheng]

Like global slab shrink, this commit also uses refcount+RCU method to make
memcg slab shrink lockless.

Use the following script to do slab shrink stress test:

```

DIR="/root/shrinker/memcg/mnt"

do_create()
{
    mkdir -p /sys/fs/cgroup/memory/test
    echo 4G > /sys/fs/cgroup/memory/test/memory.limit_in_bytes
    for i in `seq 0 $1`;
    do
        mkdir -p /sys/fs/cgroup/memory/test/$i;
        echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
        mkdir -p $DIR/$i;
    done
}

do_mount()
{
    for i in `seq $1 $2`;
    do
        mount -t tmpfs $i $DIR/$i;
    done
}

do_touch()
{
    for i in `seq $1 $2`;
    do
        echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs;
        dd if=/dev/zero of=$DIR/$i/file$i bs=1M count=1 &
    done
}

case "$1" in
  touch)
    do_touch $2 $3
    ;;
  test)
    do_create 4000
    do_mount 0 4000
    do_touch 0 3000
    ;;
  *)
    exit 1
    ;;
esac
```

Save the above script, then run test and touch commands. Then we can use
the following perf command to view hotspots:

perf top -U -F 999

1) Before applying this patchset:

  40.44%  [kernel]            [k] down_read_trylock
  17.59%  [kernel]            [k] up_read
  13.64%  [kernel]            [k] pv_native_safe_halt
  11.90%  [kernel]            [k] shrink_slab
   8.21%  [kernel]            [k] idr_find
   2.71%  [kernel]            [k] _find_next_bit
   1.36%  [kernel]            [k] shrink_node
   0.81%  [kernel]            [k] shrink_lruvec
   0.80%  [kernel]            [k] __radix_tree_lookup
   0.50%  [kernel]            [k] do_shrink_slab
   0.21%  [kernel]            [k] list_lru_count_one
   0.16%  [kernel]            [k] mem_cgroup_iter

2) After applying this patchset:

  60.17%  [kernel]           [k] shrink_slab
  20.42%  [kernel]           [k] pv_native_safe_halt
   3.03%  [kernel]           [k] do_shrink_slab
   2.73%  [kernel]           [k] shrink_node
   2.27%  [kernel]           [k] shrink_lruvec
   2.00%  [kernel]           [k] __rcu_read_unlock
   1.92%  [kernel]           [k] mem_cgroup_iter
   0.98%  [kernel]           [k] __rcu_read_lock
   0.91%  [kernel]           [k] osq_lock
   0.63%  [kernel]           [k] mem_cgroup_calculate_protection
   0.55%  [kernel]           [k] shrinker_put
   0.46%  [kernel]           [k] list_lru_count_one

We can see that the first perf hotspot becomes shrink_slab, which is what
we expect.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/shrinker.c       | 121 +++++++++++++++++++++++++++-----------------
 mm/shrinker_debug.c |   4 +-
 2 files changed, 76 insertions(+), 49 deletions(-)

diff --git a/mm/shrinker.c b/mm/shrinker.c
index 8e3334749552..744361afd520 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -107,6 +107,12 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
 					 lockdep_is_held(&shrinker_rwsem));
 }
 
+static struct shrinker_info *shrinker_info_rcu(struct mem_cgroup *memcg,
+					       int nid)
+{
+	return rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+}
+
 static int expand_one_shrinker_info(struct mem_cgroup *memcg, int new_size,
 				    int old_size, int new_nr_max)
 {
@@ -152,11 +158,11 @@ static int expand_shrinker_info(int new_id)
 	int new_size, old_size = 0;
 	struct mem_cgroup *memcg;
 
+	down_write(&shrinker_rwsem);
+
 	if (!root_mem_cgroup)
 		goto out;
 
-	lockdep_assert_held(&shrinker_rwsem);
-
 	new_size = shrinker_unit_size(new_nr_max);
 	old_size = shrinker_unit_size(shrinker_nr_max);
 
@@ -173,6 +179,8 @@ static int expand_shrinker_info(int new_id)
 	if (!ret)
 		shrinker_nr_max = new_nr_max;
 
+	up_write(&shrinker_rwsem);
+
 	return ret;
 }
 
@@ -198,7 +206,7 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 		struct shrinker_info_unit *unit;
 
 		rcu_read_lock();
-		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+		info = shrinker_info_rcu(memcg, nid);
 		unit = info->unit[shriner_id_to_index(shrinker_id)];
 		if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
 			/* Pairs with smp mb in shrink_slab() */
@@ -211,39 +219,40 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 
 static DEFINE_IDR(shrinker_idr);
 
-static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+static int shrinker_memcg_alloc(struct shrinker *shrinker)
 {
-	int id, ret = -ENOMEM;
+	int id;
 
 	if (mem_cgroup_disabled())
 		return -ENOSYS;
 
-	down_write(&shrinker_rwsem);
-	/* This may call shrinker, so it must use down_read_trylock() */
-	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
+	spin_lock(&shrinker_lock);
+	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_ATOMIC);
+	spin_unlock(&shrinker_lock);
+
 	if (id < 0)
-		goto unlock;
+		return -ENOMEM;
 
 	if (id >= shrinker_nr_max) {
 		if (expand_shrinker_info(id)) {
+			spin_lock(&shrinker_lock);
 			idr_remove(&shrinker_idr, id);
-			goto unlock;
+			spin_unlock(&shrinker_lock);
+			return -ENOMEM;
 		}
 	}
 	shrinker->id = id;
-	ret = 0;
-unlock:
-	up_write(&shrinker_rwsem);
-	return ret;
+
+	return 0;
 }
 
-static void unregister_memcg_shrinker(struct shrinker *shrinker)
+static void shrinker_memcg_remove(struct shrinker *shrinker)
 {
 	int id = shrinker->id;
 
 	BUG_ON(id < 0);
 
-	lockdep_assert_held(&shrinker_rwsem);
+	lockdep_assert_held(&shrinker_lock);
 
 	idr_remove(&shrinker_idr, id);
 }
@@ -253,10 +262,15 @@ static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
 {
 	struct shrinker_info *info;
 	struct shrinker_info_unit *unit;
+	long nr_deferred;
 
-	info = shrinker_info_protected(memcg, nid);
+	rcu_read_lock();
+	info = shrinker_info_rcu(memcg, nid);
 	unit = info->unit[shriner_id_to_index(shrinker->id)];
-	return atomic_long_xchg(&unit->nr_deferred[shriner_id_to_offset(shrinker->id)], 0);
+	nr_deferred = atomic_long_xchg(&unit->nr_deferred[shriner_id_to_offset(shrinker->id)], 0);
+	rcu_read_unlock();
+
+	return nr_deferred;
 }
 
 static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
@@ -264,10 +278,16 @@ static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
 {
 	struct shrinker_info *info;
 	struct shrinker_info_unit *unit;
+	long nr_deferred;
 
-	info = shrinker_info_protected(memcg, nid);
+	rcu_read_lock();
+	info = shrinker_info_rcu(memcg, nid);
 	unit = info->unit[shriner_id_to_index(shrinker->id)];
-	return atomic_long_add_return(nr, &unit->nr_deferred[shriner_id_to_offset(shrinker->id)]);
+	nr_deferred =
+		atomic_long_add_return(nr, &unit->nr_deferred[shriner_id_to_offset(shrinker->id)]);
+	rcu_read_unlock();
+
+	return nr_deferred;
 }
 
 void reparent_shrinker_deferred(struct mem_cgroup *memcg)
@@ -299,12 +319,12 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 	up_read(&shrinker_rwsem);
 }
 #else
-static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+static int shrinker_memcg_alloc(struct shrinker *shrinker)
 {
 	return -ENOSYS;
 }
 
-static void unregister_memcg_shrinker(struct shrinker *shrinker)
+static void shrinker_memcg_remove(struct shrinker *shrinker)
 {
 }
 
@@ -458,6 +478,8 @@ void shrinker_put(struct shrinker *shrinker)
 	if (refcount_dec_and_test(&shrinker->refcount)) {
 		spin_lock(&shrinker_lock);
 		list_del_rcu(&shrinker->list);
+		if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+			shrinker_memcg_remove(shrinker);
 		spin_unlock(&shrinker_lock);
 
 		kfree(shrinker->nr_deferred);
@@ -476,18 +498,23 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 	if (!mem_cgroup_online(memcg))
 		return 0;
 
-	if (!down_read_trylock(&shrinker_rwsem))
-		return 0;
-
-	info = shrinker_info_protected(memcg, nid);
+again:
+	rcu_read_lock();
+	info = shrinker_info_rcu(memcg, nid);
 	if (unlikely(!info))
 		goto unlock;
 
-	for (; index < shriner_id_to_index(info->map_nr_max); index++) {
+	if (index < shriner_id_to_index(info->map_nr_max)) {
 		struct shrinker_info_unit *unit;
 
 		unit = info->unit[index];
 
+		/*
+		 * The shrinker_info_unit will not be freed, so we can
+		 * safely release the RCU lock here.
+		 */
+		rcu_read_unlock();
+
 		for_each_set_bit(offset, unit->map, SHRINKER_UNIT_BITS) {
 			struct shrink_control sc = {
 				.gfp_mask = gfp_mask,
@@ -497,13 +524,14 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			struct shrinker *shrinker;
 			int shrinker_id = calc_shrinker_id(index, offset);
 
+			rcu_read_lock();
 			shrinker = idr_find(&shrinker_idr, shrinker_id);
-			if (unlikely(!shrinker ||
-				     !READ_ONCE(shrinker->registered))) {
-				if (!shrinker)
-					clear_bit(offset, unit->map);
+			if (unlikely(!shrinker || !shrinker_try_get(shrinker))) {
+				clear_bit(offset, unit->map);
+				rcu_read_unlock();
 				continue;
 			}
+			rcu_read_unlock();
 
 			/* Call non-slab shrinkers even though kmem is disabled */
 			if (!memcg_kmem_online() &&
@@ -536,15 +564,20 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 					set_shrinker_bit(memcg, nid, shrinker_id);
 			}
 			freed += ret;
-
-			if (rwsem_is_contended(&shrinker_rwsem)) {
-				freed = freed ? : 1;
-				goto unlock;
-			}
+			shrinker_put(shrinker);
 		}
+
+		/*
+		 * We have already exited the read-side of rcu critical section
+		 * before calling do_shrink_slab(), the shrinker_info may be
+		 * released in expand_one_shrinker_info(), so reacquire the
+		 * shrinker_info.
+		 */
+		index++;
+		goto again;
 	}
 unlock:
-	up_read(&shrinker_rwsem);
+	rcu_read_unlock();
 	return freed;
 }
 #else /* !CONFIG_MEMCG */
@@ -652,7 +685,7 @@ struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...)
 	shrinker->flags = flags;
 
 	if (flags & SHRINKER_MEMCG_AWARE) {
-		err = prealloc_memcg_shrinker(shrinker);
+		err = shrinker_memcg_alloc(shrinker);
 		if (err == -ENOSYS)
 			shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
 		else if (err == 0)
@@ -697,9 +730,9 @@ void shrinker_free_non_registered(struct shrinker *shrinker)
 	shrinker->name = NULL;
 #endif
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
-		down_write(&shrinker_rwsem);
-		unregister_memcg_shrinker(shrinker);
-		up_write(&shrinker_rwsem);
+		spin_lock(&shrinker_lock);
+		shrinker_memcg_remove(shrinker);
+		spin_unlock(&shrinker_lock);
 	}
 
 	kfree(shrinker->nr_deferred);
@@ -731,13 +764,7 @@ void shrinker_unregister(struct shrinker *shrinker)
 		return;
 
 	WRITE_ONCE(shrinker->registered, false);
-
-	down_write(&shrinker_rwsem);
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		unregister_memcg_shrinker(shrinker);
 	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
-	up_write(&shrinker_rwsem);
-
 	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
 
 	shrinker_put(shrinker);
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index c5573066adbf..badda35464c3 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -246,8 +246,7 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
 {
 	struct dentry *entry = shrinker->debugfs_entry;
 
-	lockdep_assert_held(&shrinker_rwsem);
-
+	down_write(&shrinker_rwsem);
 	kfree_const(shrinker->name);
 	shrinker->name = NULL;
 
@@ -258,6 +257,7 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
 	 */
 	smp_wmb();
 	shrinker->debugfs_entry = NULL;
+	up_write(&shrinker_rwsem);
 
 	return entry;
 }
-- 
2.30.2

[PATCH v2 46/47] mm: shrinker: hold write lock to reparent shrinker nr_deferred

[Qi Zheng]

For now, reparent_shrinker_deferred() is the only holder of read lock of
shrinker_rwsem. And it already holds the global cgroup_mutex, so it will
not be called in parallel.

Therefore, in order to convert shrinker_rwsem to shrinker_mutex later,
here we change to hold the write lock of shrinker_rwsem to reparent.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/shrinker.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/shrinker.c b/mm/shrinker.c
index 744361afd520..90c045620fe3 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -303,7 +303,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 		parent = root_mem_cgroup;
 
 	/* Prevent from concurrent shrinker_info expand */
-	down_read(&shrinker_rwsem);
+	down_write(&shrinker_rwsem);
 	for_each_node(nid) {
 		child_info = shrinker_info_protected(memcg, nid);
 		parent_info = shrinker_info_protected(parent, nid);
@@ -316,7 +316,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 			}
 		}
 	}
-	up_read(&shrinker_rwsem);
+	up_write(&shrinker_rwsem);
 }
 #else
 static int shrinker_memcg_alloc(struct shrinker *shrinker)
-- 
2.30.2

[PATCH v2 47/47] mm: shrinker: convert shrinker_rwsem to mutex

[Qi Zheng]

Now there are no readers of shrinker_rwsem, so we can simply replace it
with mutex lock.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 drivers/md/dm-cache-metadata.c |  2 +-
 fs/super.c                     |  2 +-
 mm/shrinker.c                  | 16 ++++++++--------
 mm/shrinker_debug.c            | 14 +++++++-------
 4 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index acffed750e3e..9e0c69958587 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -1828,7 +1828,7 @@ int dm_cache_metadata_abort(struct dm_cache_metadata *cmd)
 	 * Replacement block manager (new_bm) is created and old_bm destroyed outside of
 	 * cmd root_lock to avoid ABBA deadlock that would result (due to life-cycle of
 	 * shrinker associated with the block manager's bufio client vs cmd root_lock).
-	 * - must take shrinker_rwsem without holding cmd->root_lock
+	 * - must take shrinker_mutex without holding cmd->root_lock
 	 */
 	new_bm = dm_block_manager_create(cmd->bdev, DM_CACHE_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
 					 CACHE_MAX_CONCURRENT_LOCKS);
diff --git a/fs/super.c b/fs/super.c
index 04643fd80886..602cf54eb7da 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -54,7 +54,7 @@ static char *sb_writers_name[SB_FREEZE_LEVELS] = {
  * One thing we have to be careful of with a per-sb shrinker is that we don't
  * drop the last active reference to the superblock from within the shrinker.
  * If that happens we could trigger unregistering the shrinker from within the
- * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
+ * shrinker path and that leads to deadlock on the shrinker_mutex. Hence we
  * take a passive reference to the superblock to avoid this from occurring.
  */
 static unsigned long super_cache_scan(struct shrinker *shrink,
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 90c045620fe3..5c4546d2c234 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -7,7 +7,7 @@
 #include <trace/events/vmscan.h>
 
 LIST_HEAD(shrinker_list);
-DECLARE_RWSEM(shrinker_rwsem);
+DEFINE_MUTEX(shrinker_mutex);
 DEFINE_SPINLOCK(shrinker_lock);
 
 #ifdef CONFIG_MEMCG
@@ -80,7 +80,7 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 	int nid, ret = 0;
 	int array_size = 0;
 
-	down_write(&shrinker_rwsem);
+	mutex_lock(&shrinker_mutex);
 	array_size = shrinker_unit_size(shrinker_nr_max);
 	for_each_node(nid) {
 		info = kvzalloc_node(sizeof(*info) + array_size, GFP_KERNEL, nid);
@@ -91,7 +91,7 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 			goto err;
 		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
 	}
-	up_write(&shrinker_rwsem);
+	mutex_unlock(&shrinker_mutex);
 
 	return ret;
 
@@ -104,7 +104,7 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
 						     int nid)
 {
 	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
-					 lockdep_is_held(&shrinker_rwsem));
+					 lockdep_is_held(&shrinker_mutex));
 }
 
 static struct shrinker_info *shrinker_info_rcu(struct mem_cgroup *memcg,
@@ -158,7 +158,7 @@ static int expand_shrinker_info(int new_id)
 	int new_size, old_size = 0;
 	struct mem_cgroup *memcg;
 
-	down_write(&shrinker_rwsem);
+	mutex_lock(&shrinker_mutex);
 
 	if (!root_mem_cgroup)
 		goto out;
@@ -179,7 +179,7 @@ static int expand_shrinker_info(int new_id)
 	if (!ret)
 		shrinker_nr_max = new_nr_max;
 
-	up_write(&shrinker_rwsem);
+	mutex_unlock(&shrinker_mutex);
 
 	return ret;
 }
@@ -303,7 +303,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 		parent = root_mem_cgroup;
 
 	/* Prevent from concurrent shrinker_info expand */
-	down_write(&shrinker_rwsem);
+	mutex_lock(&shrinker_mutex);
 	for_each_node(nid) {
 		child_info = shrinker_info_protected(memcg, nid);
 		parent_info = shrinker_info_protected(parent, nid);
@@ -316,7 +316,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 			}
 		}
 	}
-	up_write(&shrinker_rwsem);
+	mutex_unlock(&shrinker_mutex);
 }
 #else
 static int shrinker_memcg_alloc(struct shrinker *shrinker)
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index badda35464c3..44b620b1919d 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -8,7 +8,7 @@
 #include <linux/rculist.h>
 
 /* defined in vmscan.c */
-extern struct rw_semaphore shrinker_rwsem;
+extern struct mutex shrinker_mutex;
 extern struct list_head shrinker_list;
 
 static DEFINE_IDA(shrinker_debugfs_ida);
@@ -168,7 +168,7 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
 	if (!shrinker_debugfs_root)
 		return 0;
 
-	down_write(&shrinker_rwsem);
+	mutex_lock(&shrinker_mutex);
 	if (shrinker->debugfs_entry)
 		goto fail;
 
@@ -196,7 +196,7 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
 			    &shrinker_debugfs_scan_fops);
 
 fail:
-	up_write(&shrinker_rwsem);
+	mutex_unlock(&shrinker_mutex);
 	return ret;
 }
 
@@ -215,7 +215,7 @@ int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
 	if (!new)
 		return -ENOMEM;
 
-	down_write(&shrinker_rwsem);
+	mutex_lock(&shrinker_mutex);
 
 	old = shrinker->name;
 	shrinker->name = new;
@@ -233,7 +233,7 @@ int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
 			shrinker->debugfs_entry = entry;
 	}
 
-	up_write(&shrinker_rwsem);
+	mutex_unlock(&shrinker_mutex);
 
 	kfree_const(old);
 
@@ -246,7 +246,7 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
 {
 	struct dentry *entry = shrinker->debugfs_entry;
 
-	down_write(&shrinker_rwsem);
+	mutex_lock(&shrinker_mutex);
 	kfree_const(shrinker->name);
 	shrinker->name = NULL;
 
@@ -257,7 +257,7 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
 	 */
 	smp_wmb();
 	shrinker->debugfs_entry = NULL;
-	up_write(&shrinker_rwsem);
+	mutex_unlock(&shrinker_mutex);
 
 	return entry;
 }
-- 
2.30.2

Re: [PATCH v2 05/47] binder: dynamically allocate the android-binder shrinker

[Qi Zheng]

This patch depends on the patch: 
https://lore.kernel.org/lkml/20230625154937.64316-1-qi.zheng@linux.dev/

Re: [PATCH v2 24/47] drm/panfrost: dynamically allocate the drm-panfrost shrinker

[Steven Price]

On 24/07/2023 10:43, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the drm-panfrost shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct panfrost_device.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

One nit below, but otherwise:

Reviewed-by: Steven Price <steven.price@arm.com>

> ---
>  drivers/gpu/drm/panfrost/panfrost_device.h    |  2 +-
>  drivers/gpu/drm/panfrost/panfrost_drv.c       |  6 +++-
>  drivers/gpu/drm/panfrost/panfrost_gem.h       |  2 +-
>  .../gpu/drm/panfrost/panfrost_gem_shrinker.c  | 32 ++++++++++++-------
>  4 files changed, 27 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index b0126b9fbadc..e667e5689353 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -118,7 +118,7 @@ struct panfrost_device {
>  
>  	struct mutex shrinker_lock;
>  	struct list_head shrinker_list;
> -	struct shrinker shrinker;
> +	struct shrinker *shrinker;
>  
>  	struct panfrost_devfreq pfdevfreq;
>  };
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index bbada731bbbd..f705bbdea360 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -598,10 +598,14 @@ static int panfrost_probe(struct platform_device *pdev)
>  	if (err < 0)
>  		goto err_out1;
>  
> -	panfrost_gem_shrinker_init(ddev);
> +	err = panfrost_gem_shrinker_init(ddev);
> +	if (err)
> +		goto err_out2;
>  
>  	return 0;
>  
> +err_out2:
> +	drm_dev_unregister(ddev);
>  err_out1:
>  	pm_runtime_disable(pfdev->dev);
>  	panfrost_device_fini(pfdev);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index ad2877eeeccd..863d2ec8d4f0 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -81,7 +81,7 @@ panfrost_gem_mapping_get(struct panfrost_gem_object *bo,
>  void panfrost_gem_mapping_put(struct panfrost_gem_mapping *mapping);
>  void panfrost_gem_teardown_mappings_locked(struct panfrost_gem_object *bo);
>  
> -void panfrost_gem_shrinker_init(struct drm_device *dev);
> +int panfrost_gem_shrinker_init(struct drm_device *dev);
>  void panfrost_gem_shrinker_cleanup(struct drm_device *dev);
>  
>  #endif /* __PANFROST_GEM_H__ */
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> index bf0170782f25..9a90dfb5301f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> @@ -18,8 +18,7 @@
>  static unsigned long
>  panfrost_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
>  {
> -	struct panfrost_device *pfdev =
> -		container_of(shrinker, struct panfrost_device, shrinker);
> +	struct panfrost_device *pfdev = shrinker->private_data;
>  	struct drm_gem_shmem_object *shmem;
>  	unsigned long count = 0;
>  
> @@ -65,8 +64,7 @@ static bool panfrost_gem_purge(struct drm_gem_object *obj)
>  static unsigned long
>  panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>  {
> -	struct panfrost_device *pfdev =
> -		container_of(shrinker, struct panfrost_device, shrinker);
> +	struct panfrost_device *pfdev = shrinker->private_data;
>  	struct drm_gem_shmem_object *shmem, *tmp;
>  	unsigned long freed = 0;
>  
> @@ -97,13 +95,24 @@ panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>   *
>   * This function registers and sets up the panfrost shrinker.
>   */
> -void panfrost_gem_shrinker_init(struct drm_device *dev)
> +int panfrost_gem_shrinker_init(struct drm_device *dev)
>  {
>  	struct panfrost_device *pfdev = dev->dev_private;
> -	pfdev->shrinker.count_objects = panfrost_gem_shrinker_count;
> -	pfdev->shrinker.scan_objects = panfrost_gem_shrinker_scan;
> -	pfdev->shrinker.seeks = DEFAULT_SEEKS;
> -	WARN_ON(register_shrinker(&pfdev->shrinker, "drm-panfrost"));
> +
> +	pfdev->shrinker = shrinker_alloc(0, "drm-panfrost");
> +	if (!pfdev->shrinker) {
> +		WARN_ON(1);

I don't think this WARN_ON is particularly useful - if there's a failed
memory allocation we should see output from the kernel anyway. And we're
changing the semantics from "continue just without a shrinker" (which
argueably justifies the warning) to "probe fails, device doesn't work"
which will be obvious to the user so I don't feel we need the additional
warn.

> +		return -ENOMEM;
> +	}
> +
> +	pfdev->shrinker->count_objects = panfrost_gem_shrinker_count;
> +	pfdev->shrinker->scan_objects = panfrost_gem_shrinker_scan;
> +	pfdev->shrinker->seeks = DEFAULT_SEEKS;
> +	pfdev->shrinker->private_data = pfdev;
> +
> +	shrinker_register(pfdev->shrinker);
> +
> +	return 0;
>  }
>  
>  /**
> @@ -116,7 +125,6 @@ void panfrost_gem_shrinker_cleanup(struct drm_device *dev)
>  {
>  	struct panfrost_device *pfdev = dev->dev_private;
>  
> -	if (pfdev->shrinker.nr_deferred) {
> -		unregister_shrinker(&pfdev->shrinker);
> -	}
> +	if (pfdev->shrinker)
> +		shrinker_unregister(pfdev->shrinker);
>  }

Re: [PATCH v2 34/47] nfsd: dynamically allocate the nfsd-client shrinker

[Jeff Layton]

On Mon, 2023-07-24 at 17:43 +0800, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the nfsd-client shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct nfsd_net.
> 
> Acked-by: Chuck Lever <chuck.lever@oracle.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>  fs/nfsd/netns.h     |  2 +-
>  fs/nfsd/nfs4state.c | 20 ++++++++++++--------
>  2 files changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index ec49b200b797..f669444d5336 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -195,7 +195,7 @@ struct nfsd_net {
>  	int			nfs4_max_clients;
>  
>  	atomic_t		nfsd_courtesy_clients;
> -	struct shrinker		nfsd_client_shrinker;
> +	struct shrinker		*nfsd_client_shrinker;
>  	struct work_struct	nfsd_shrinker_work;
>  };
>  
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 3339177f8e2f..c7a4616cd866 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -4388,8 +4388,7 @@ static unsigned long
>  nfsd4_state_shrinker_count(struct shrinker *shrink, struct shrink_control *sc)
>  {
>  	int count;
> -	struct nfsd_net *nn = container_of(shrink,
> -			struct nfsd_net, nfsd_client_shrinker);
> +	struct nfsd_net *nn = shrink->private_data;
>  
>  	count = atomic_read(&nn->nfsd_courtesy_clients);
>  	if (!count)
> @@ -8125,12 +8124,17 @@ static int nfs4_state_create_net(struct net *net)
>  	INIT_WORK(&nn->nfsd_shrinker_work, nfsd4_state_shrinker_worker);
>  	get_net(net);
>  
> -	nn->nfsd_client_shrinker.scan_objects = nfsd4_state_shrinker_scan;
> -	nn->nfsd_client_shrinker.count_objects = nfsd4_state_shrinker_count;
> -	nn->nfsd_client_shrinker.seeks = DEFAULT_SEEKS;
> -
> -	if (register_shrinker(&nn->nfsd_client_shrinker, "nfsd-client"))
> +	nn->nfsd_client_shrinker = shrinker_alloc(0, "nfsd-client");
> +	if (!nn->nfsd_client_shrinker)
>  		goto err_shrinker;
> +
> +	nn->nfsd_client_shrinker->scan_objects = nfsd4_state_shrinker_scan;
> +	nn->nfsd_client_shrinker->count_objects = nfsd4_state_shrinker_count;
> +	nn->nfsd_client_shrinker->seeks = DEFAULT_SEEKS;
> +	nn->nfsd_client_shrinker->private_data = nn;
> +
> +	shrinker_register(nn->nfsd_client_shrinker);
> +
>  	return 0;
>  
>  err_shrinker:
> @@ -8228,7 +8232,7 @@ nfs4_state_shutdown_net(struct net *net)
>  	struct list_head *pos, *next, reaplist;
>  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>  
> -	unregister_shrinker(&nn->nfsd_client_shrinker);
> +	shrinker_unregister(nn->nfsd_client_shrinker);
>  	cancel_work(&nn->nfsd_shrinker_work);
>  	cancel_delayed_work_sync(&nn->laundromat_work);
>  	locks_end_grace(&nn->nfsd4_manager);

Acked-by: Jeff Layton <jlayton@kernel.org>

Re: [PATCH v2 35/47] nfsd: dynamically allocate the nfsd-reply shrinker

[Jeff Layton]

On Mon, 2023-07-24 at 17:43 +0800, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the nfsd-reply shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct nfsd_net.
> 
> Acked-by: Chuck Lever <chuck.lever@oracle.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>  fs/nfsd/netns.h    |  2 +-
>  fs/nfsd/nfscache.c | 31 ++++++++++++++++---------------
>  2 files changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index f669444d5336..ab303a8b77d5 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -177,7 +177,7 @@ struct nfsd_net {
>  	/* size of cache when we saw the longest hash chain */
>  	unsigned int             longest_chain_cachesize;
>  
> -	struct shrinker		nfsd_reply_cache_shrinker;
> +	struct shrinker		*nfsd_reply_cache_shrinker;
>  
>  	/* tracking server-to-server copy mounts */
>  	spinlock_t              nfsd_ssc_lock;
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index 6eb3d7bdfaf3..9f0ab65e4125 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -200,26 +200,29 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
>  {
>  	unsigned int hashsize;
>  	unsigned int i;
> -	int status = 0;
>  
>  	nn->max_drc_entries = nfsd_cache_size_limit();
>  	atomic_set(&nn->num_drc_entries, 0);
>  	hashsize = nfsd_hashsize(nn->max_drc_entries);
>  	nn->maskbits = ilog2(hashsize);
>  
> -	nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
> -	nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
> -	nn->nfsd_reply_cache_shrinker.seeks = 1;
> -	status = register_shrinker(&nn->nfsd_reply_cache_shrinker,
> -				   "nfsd-reply:%s", nn->nfsd_name);
> -	if (status)
> -		return status;
> -
>  	nn->drc_hashtbl = kvzalloc(array_size(hashsize,
>  				sizeof(*nn->drc_hashtbl)), GFP_KERNEL);
>  	if (!nn->drc_hashtbl)
> +		return -ENOMEM;
> +
> +	nn->nfsd_reply_cache_shrinker = shrinker_alloc(0, "nfsd-reply:%s",
> +						       nn->nfsd_name);
> +	if (!nn->nfsd_reply_cache_shrinker)
>  		goto out_shrinker;
>  
> +	nn->nfsd_reply_cache_shrinker->scan_objects = nfsd_reply_cache_scan;
> +	nn->nfsd_reply_cache_shrinker->count_objects = nfsd_reply_cache_count;
> +	nn->nfsd_reply_cache_shrinker->seeks = 1;
> +	nn->nfsd_reply_cache_shrinker->private_data = nn;
> +
> +	shrinker_register(nn->nfsd_reply_cache_shrinker);
> +
>  	for (i = 0; i < hashsize; i++) {
>  		INIT_LIST_HEAD(&nn->drc_hashtbl[i].lru_head);
>  		spin_lock_init(&nn->drc_hashtbl[i].cache_lock);
> @@ -228,7 +231,7 @@ int nfsd_reply_cache_init(struct nfsd_net *nn)
>  
>  	return 0;
>  out_shrinker:
> -	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
> +	kvfree(nn->drc_hashtbl);
>  	printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
>  	return -ENOMEM;
>  }
> @@ -238,7 +241,7 @@ void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
>  	struct nfsd_cacherep *rp;
>  	unsigned int i;
>  
> -	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
> +	shrinker_unregister(nn->nfsd_reply_cache_shrinker);
>  
>  	for (i = 0; i < nn->drc_hashsize; i++) {
>  		struct list_head *head = &nn->drc_hashtbl[i].lru_head;
> @@ -322,8 +325,7 @@ nfsd_prune_bucket_locked(struct nfsd_net *nn, struct nfsd_drc_bucket *b,
>  static unsigned long
>  nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
>  {
> -	struct nfsd_net *nn = container_of(shrink,
> -				struct nfsd_net, nfsd_reply_cache_shrinker);
> +	struct nfsd_net *nn = shrink->private_data;
>  
>  	return atomic_read(&nn->num_drc_entries);
>  }
> @@ -342,8 +344,7 @@ nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
>  static unsigned long
>  nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
>  {
> -	struct nfsd_net *nn = container_of(shrink,
> -				struct nfsd_net, nfsd_reply_cache_shrinker);
> +	struct nfsd_net *nn = shrink->private_data;
>  	unsigned long freed = 0;
>  	LIST_HEAD(dispose);
>  	unsigned int i;

Acked-by: Jeff Layton <jlayton@kernel.org>

Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Peter Zijlstra]

On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote:

> +void shrinker_unregister(struct shrinker *shrinker)
> +{
> +	struct dentry *debugfs_entry;
> +	int debugfs_id;
> +
> +	if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))
> +		return;
> +
> +	down_write(&shrinker_rwsem);
> +	list_del(&shrinker->list);
> +	shrinker->flags &= ~SHRINKER_REGISTERED;
> +	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> +		unregister_memcg_shrinker(shrinker);
> +	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
> +	up_write(&shrinker_rwsem);
> +
> +	shrinker_debugfs_remove(debugfs_entry, debugfs_id);

Should there not be an rcu_barrier() right about here?

> +
> +	kfree(shrinker->nr_deferred);
> +	shrinker->nr_deferred = NULL;
> +
> +	kfree(shrinker);
> +}
> +EXPORT_SYMBOL(shrinker_unregister);

Re: [PATCH v2 01/47] mm: vmscan: move shrinker-related code into a separate file

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> The mm/vmscan.c file is too large, so separate the shrinker-related
> code from it into a separate file. No functional changes.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
> include/linux/shrinker.h |   3 +
> mm/Makefile              |   4 +-
> mm/shrinker.c            | 707 +++++++++++++++++++++++++++++++++++++++
> mm/vmscan.c              | 701 --------------------------------------
> 4 files changed, 712 insertions(+), 703 deletions(-)
> create mode 100644 mm/shrinker.c
> 
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index 224293b2dd06..961cb84e51f5 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -96,6 +96,9 @@ struct shrinker {
>  */
> #define SHRINKER_NONSLAB (1 << 3)
> 
> +unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
> +			   int priority);

A good cleanup, vmscan.c is so huge.

I'd like to introduce a new header in mm/ directory and contains those
declarations of functions (like this and other debug function in
shrinker_debug.c) since they are used internally across mm.

Thanks.

Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Qi Zheng]

Hi Peter,

On 2023/7/24 20:25, Peter Zijlstra wrote:
> On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote:
> 
>> +void shrinker_unregister(struct shrinker *shrinker)
>> +{
>> +	struct dentry *debugfs_entry;
>> +	int debugfs_id;
>> +
>> +	if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))
>> +		return;
>> +
>> +	down_write(&shrinker_rwsem);
>> +	list_del(&shrinker->list);
>> +	shrinker->flags &= ~SHRINKER_REGISTERED;
>> +	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>> +		unregister_memcg_shrinker(shrinker);
>> +	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
>> +	up_write(&shrinker_rwsem);
>> +
>> +	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
> 
> Should there not be an rcu_barrier() right about here?

The shrinker_debugfs_remove() will wait for debugfs_file_put() to
return, so when running here, all shrinker debugfs operations have
been completed. And the slab shrink will hold the read lock of
shrinker_rwsem to traverse the shrinker_list, so when we hold the
write lock of shrinker_rwsem to delete the shrinker from the
shrinker_list, the shrinker will not be executed again.

So I think there is no need to add a rcu_barrier() here. Please let
me know if I missed something.

Thanks,
Qi

> 
>> +
>> +	kfree(shrinker->nr_deferred);
>> +	shrinker->nr_deferred = NULL;
>> +
>> +	kfree(shrinker);
>> +}
>> +EXPORT_SYMBOL(shrinker_unregister);
> 

Re: [PATCH v2 24/47] drm/panfrost: dynamically allocate the drm-panfrost shrinker

[Qi Zheng]

Hi Steven,

On 2023/7/24 19:17, Steven Price wrote:
> On 24/07/2023 10:43, Qi Zheng wrote:
>> In preparation for implementing lockless slab shrink, use new APIs to
>> dynamically allocate the drm-panfrost shrinker, so that it can be freed
>> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
>> read-side critical section when releasing the struct panfrost_device.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> One nit below, but otherwise:
> 
> Reviewed-by: Steven Price <steven.price@arm.com>
> 
>> ---
>>   drivers/gpu/drm/panfrost/panfrost_device.h    |  2 +-
>>   drivers/gpu/drm/panfrost/panfrost_drv.c       |  6 +++-
>>   drivers/gpu/drm/panfrost/panfrost_gem.h       |  2 +-
>>   .../gpu/drm/panfrost/panfrost_gem_shrinker.c  | 32 ++++++++++++-------
>>   4 files changed, 27 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
>> index b0126b9fbadc..e667e5689353 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
>> @@ -118,7 +118,7 @@ struct panfrost_device {
>>   
>>   	struct mutex shrinker_lock;
>>   	struct list_head shrinker_list;
>> -	struct shrinker shrinker;
>> +	struct shrinker *shrinker;
>>   
>>   	struct panfrost_devfreq pfdevfreq;
>>   };
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> index bbada731bbbd..f705bbdea360 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> @@ -598,10 +598,14 @@ static int panfrost_probe(struct platform_device *pdev)
>>   	if (err < 0)
>>   		goto err_out1;
>>   
>> -	panfrost_gem_shrinker_init(ddev);
>> +	err = panfrost_gem_shrinker_init(ddev);
>> +	if (err)
>> +		goto err_out2;
>>   
>>   	return 0;
>>   
>> +err_out2:
>> +	drm_dev_unregister(ddev);
>>   err_out1:
>>   	pm_runtime_disable(pfdev->dev);
>>   	panfrost_device_fini(pfdev);
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
>> index ad2877eeeccd..863d2ec8d4f0 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
>> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
>> @@ -81,7 +81,7 @@ panfrost_gem_mapping_get(struct panfrost_gem_object *bo,
>>   void panfrost_gem_mapping_put(struct panfrost_gem_mapping *mapping);
>>   void panfrost_gem_teardown_mappings_locked(struct panfrost_gem_object *bo);
>>   
>> -void panfrost_gem_shrinker_init(struct drm_device *dev);
>> +int panfrost_gem_shrinker_init(struct drm_device *dev);
>>   void panfrost_gem_shrinker_cleanup(struct drm_device *dev);
>>   
>>   #endif /* __PANFROST_GEM_H__ */
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
>> index bf0170782f25..9a90dfb5301f 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
>> @@ -18,8 +18,7 @@
>>   static unsigned long
>>   panfrost_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
>>   {
>> -	struct panfrost_device *pfdev =
>> -		container_of(shrinker, struct panfrost_device, shrinker);
>> +	struct panfrost_device *pfdev = shrinker->private_data;
>>   	struct drm_gem_shmem_object *shmem;
>>   	unsigned long count = 0;
>>   
>> @@ -65,8 +64,7 @@ static bool panfrost_gem_purge(struct drm_gem_object *obj)
>>   static unsigned long
>>   panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>>   {
>> -	struct panfrost_device *pfdev =
>> -		container_of(shrinker, struct panfrost_device, shrinker);
>> +	struct panfrost_device *pfdev = shrinker->private_data;
>>   	struct drm_gem_shmem_object *shmem, *tmp;
>>   	unsigned long freed = 0;
>>   
>> @@ -97,13 +95,24 @@ panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>>    *
>>    * This function registers and sets up the panfrost shrinker.
>>    */
>> -void panfrost_gem_shrinker_init(struct drm_device *dev)
>> +int panfrost_gem_shrinker_init(struct drm_device *dev)
>>   {
>>   	struct panfrost_device *pfdev = dev->dev_private;
>> -	pfdev->shrinker.count_objects = panfrost_gem_shrinker_count;
>> -	pfdev->shrinker.scan_objects = panfrost_gem_shrinker_scan;
>> -	pfdev->shrinker.seeks = DEFAULT_SEEKS;
>> -	WARN_ON(register_shrinker(&pfdev->shrinker, "drm-panfrost"));
>> +
>> +	pfdev->shrinker = shrinker_alloc(0, "drm-panfrost");
>> +	if (!pfdev->shrinker) {
>> +		WARN_ON(1);
> 
> I don't think this WARN_ON is particularly useful - if there's a failed
> memory allocation we should see output from the kernel anyway. And we're
> changing the semantics from "continue just without a shrinker" (which
> argueably justifies the warning) to "probe fails, device doesn't work"
> which will be obvious to the user so I don't feel we need the additional
> warn.

Make sense. Will delete this WARN_ON() in the next version.

Thanks,
Qi

> 
>> +		return -ENOMEM;
>> +	}
>> +
>> +	pfdev->shrinker->count_objects = panfrost_gem_shrinker_count;
>> +	pfdev->shrinker->scan_objects = panfrost_gem_shrinker_scan;
>> +	pfdev->shrinker->seeks = DEFAULT_SEEKS;
>> +	pfdev->shrinker->private_data = pfdev;
>> +
>> +	shrinker_register(pfdev->shrinker);
>> +
>> +	return 0;
>>   }
>>   
>>   /**
>> @@ -116,7 +125,6 @@ void panfrost_gem_shrinker_cleanup(struct drm_device *dev)
>>   {
>>   	struct panfrost_device *pfdev = dev->dev_private;
>>   
>> -	if (pfdev->shrinker.nr_deferred) {
>> -		unregister_shrinker(&pfdev->shrinker);
>> -	}
>> +	if (pfdev->shrinker)
>> +		shrinker_unregister(pfdev->shrinker);
>>   }
> 

Re: [PATCH v2 01/47] mm: vmscan: move shrinker-related code into a separate file

[Qi Zheng]

On 2023/7/25 10:35, Muchun Song wrote:
> 
> 
>> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>>
>> The mm/vmscan.c file is too large, so separate the shrinker-related
>> code from it into a separate file. No functional changes.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>> include/linux/shrinker.h |   3 +
>> mm/Makefile              |   4 +-
>> mm/shrinker.c            | 707 +++++++++++++++++++++++++++++++++++++++
>> mm/vmscan.c              | 701 --------------------------------------
>> 4 files changed, 712 insertions(+), 703 deletions(-)
>> create mode 100644 mm/shrinker.c
>>
>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
>> index 224293b2dd06..961cb84e51f5 100644
>> --- a/include/linux/shrinker.h
>> +++ b/include/linux/shrinker.h
>> @@ -96,6 +96,9 @@ struct shrinker {
>>   */
>> #define SHRINKER_NONSLAB (1 << 3)
>>
>> +unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
>> +			   int priority);
> 
> A good cleanup, vmscan.c is so huge.
> 
> I'd like to introduce a new header in mm/ directory and contains those
> declarations of functions (like this and other debug function in
> shrinker_debug.c) since they are used internally across mm.

How about putting them in the mm/internal.h file?

> 
> Thanks.
> 

Re: [PATCH v2 02/47] mm: shrinker: remove redundant shrinker_rwsem in debugfs operations

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> The debugfs_remove_recursive() will wait for debugfs_file_put() to return,
> so the shrinker will not be freed when doing debugfs operations (such as
> shrinker_debugfs_count_show() and shrinker_debugfs_scan_write()), so there
> is no need to hold shrinker_rwsem during debugfs operations.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.

Re: [PATCH v2 01/47] mm: vmscan: move shrinker-related code into a separate file

[Muchun Song]

> On Jul 25, 2023, at 11:09, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> 
> 
> On 2023/7/25 10:35, Muchun Song wrote:
>>> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>>> 
>>> The mm/vmscan.c file is too large, so separate the shrinker-related
>>> code from it into a separate file. No functional changes.
>>> 
>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>> ---
>>> include/linux/shrinker.h |   3 +
>>> mm/Makefile              |   4 +-
>>> mm/shrinker.c            | 707 +++++++++++++++++++++++++++++++++++++++
>>> mm/vmscan.c              | 701 --------------------------------------
>>> 4 files changed, 712 insertions(+), 703 deletions(-)
>>> create mode 100644 mm/shrinker.c
>>> 
>>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
>>> index 224293b2dd06..961cb84e51f5 100644
>>> --- a/include/linux/shrinker.h
>>> +++ b/include/linux/shrinker.h
>>> @@ -96,6 +96,9 @@ struct shrinker {
>>>  */
>>> #define SHRINKER_NONSLAB (1 << 3)
>>> 
>>> +unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
>>> +    int priority);
>> A good cleanup, vmscan.c is so huge.
>> I'd like to introduce a new header in mm/ directory and contains those
>> declarations of functions (like this and other debug function in
>> shrinker_debug.c) since they are used internally across mm.
> 
> How about putting them in the mm/internal.h file?

Either is fine to me.

> 
>> Thanks.

Re: [PATCH v2 01/47] mm: vmscan: move shrinker-related code into a separate file

[Qi Zheng]

On 2023/7/25 11:23, Muchun Song wrote:
> 
> 
>> On Jul 25, 2023, at 11:09, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>>
>>
>>
>> On 2023/7/25 10:35, Muchun Song wrote:
>>>> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>>>>
>>>> The mm/vmscan.c file is too large, so separate the shrinker-related
>>>> code from it into a separate file. No functional changes.
>>>>
>>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>>> ---
>>>> include/linux/shrinker.h |   3 +
>>>> mm/Makefile              |   4 +-
>>>> mm/shrinker.c            | 707 +++++++++++++++++++++++++++++++++++++++
>>>> mm/vmscan.c              | 701 --------------------------------------
>>>> 4 files changed, 712 insertions(+), 703 deletions(-)
>>>> create mode 100644 mm/shrinker.c
>>>>
>>>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
>>>> index 224293b2dd06..961cb84e51f5 100644
>>>> --- a/include/linux/shrinker.h
>>>> +++ b/include/linux/shrinker.h
>>>> @@ -96,6 +96,9 @@ struct shrinker {
>>>>   */
>>>> #define SHRINKER_NONSLAB (1 << 3)
>>>>
>>>> +unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
>>>> +    int priority);
>>> A good cleanup, vmscan.c is so huge.
>>> I'd like to introduce a new header in mm/ directory and contains those
>>> declarations of functions (like this and other debug function in
>>> shrinker_debug.c) since they are used internally across mm.
>>
>> How about putting them in the mm/internal.h file?
> 
> Either is fine to me.

OK, will do in the next version.

> 
>>
>>> Thanks.
> 
> 

Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Muchun Song]

On 2023/7/24 17:43, Qi Zheng wrote:
> Currently, the shrinker instances can be divided into the following three
> types:
>
> a) global shrinker instance statically defined in the kernel, such as
>     workingset_shadow_shrinker.
>
> b) global shrinker instance statically defined in the kernel modules, such
>     as mmu_shrinker in x86.
>
> c) shrinker instance embedded in other structures.
>
> For case a, the memory of shrinker instance is never freed. For case b,
> the memory of shrinker instance will be freed after synchronize_rcu() when
> the module is unloaded. For case c, the memory of shrinker instance will
> be freed along with the structure it is embedded in.
>
> In preparation for implementing lockless slab shrink, we need to
> dynamically allocate those shrinker instances in case c, then the memory
> can be dynamically freed alone by calling kfree_rcu().
>
> So this commit adds the following new APIs for dynamically allocating
> shrinker, and add a private_data field to struct shrinker to record and
> get the original embedded structure.
>
> 1. shrinker_alloc()
>
> Used to allocate shrinker instance itself and related memory, it will
> return a pointer to the shrinker instance on success and NULL on failure.
>
> 2. shrinker_free_non_registered()
>
> Used to destroy the non-registered shrinker instance.

At least I don't like this name. I know you want to tell others
this function only should be called when shrinker has not been
registed but allocated. Maybe shrinker_free() is more simple.
And and a comment to tell the users when to use it.

>
> 3. shrinker_register()
>
> Used to register the shrinker instance, which is same as the current
> register_shrinker_prepared().
>
> 4. shrinker_unregister()
>
> Used to unregister and free the shrinker instance.
>
> In order to simplify shrinker-related APIs and make shrinker more
> independent of other kernel mechanisms, subsequent submissions will use
> the above API to convert all shrinkers (including case a and b) to
> dynamically allocated, and then remove all existing APIs.
>
> This will also have another advantage mentioned by Dave Chinner:
>
> ```
> The other advantage of this is that it will break all the existing
> out of tree code and third party modules using the old API and will
> no longer work with a kernel using lockless slab shrinkers. They
> need to break (both at the source and binary levels) to stop bad
> things from happening due to using uncoverted shrinkers in the new
> setup.
> ```
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>   include/linux/shrinker.h |   6 +++
>   mm/shrinker.c            | 113 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 119 insertions(+)
>
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index 961cb84e51f5..296f5e163861 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -70,6 +70,8 @@ struct shrinker {
>   	int seeks;	/* seeks to recreate an obj */
>   	unsigned flags;
>   
> +	void *private_data;
> +
>   	/* These are for internal use */
>   	struct list_head list;
>   #ifdef CONFIG_MEMCG
> @@ -98,6 +100,10 @@ struct shrinker {
>   
>   unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
>   			  int priority);
> +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...);
> +void shrinker_free_non_registered(struct shrinker *shrinker);
> +void shrinker_register(struct shrinker *shrinker);
> +void shrinker_unregister(struct shrinker *shrinker);
>   
>   extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
>   					    const char *fmt, ...);
> diff --git a/mm/shrinker.c b/mm/shrinker.c
> index 0a32ef42f2a7..d820e4cc5806 100644
> --- a/mm/shrinker.c
> +++ b/mm/shrinker.c
> @@ -548,6 +548,119 @@ unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
>   	return freed;
>   }
>   
> +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...)
> +{
> +	struct shrinker *shrinker;
> +	unsigned int size;
> +	va_list __maybe_unused ap;
> +	int err;
> +
> +	shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL);
> +	if (!shrinker)
> +		return NULL;
> +
> +#ifdef CONFIG_SHRINKER_DEBUG
> +	va_start(ap, fmt);
> +	shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
> +	va_end(ap);
> +	if (!shrinker->name)
> +		goto err_name;
> +#endif

So why not introduce another helper to handle this and declare it
as a void function when !CONFIG_SHRINKER_DEBUG? Something like the
following:

#ifdef CONFIG_SHRINKER_DEBUG
static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const 
char *fmt,
                                        va_list vargs)

{
     shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, vargs);
     return shrinker->name ? 0 : -ENOMEM;
}
#else
static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const 
char *fmt,
                                        va_list vargs)
{
     return 0;
}
#endif

> +	shrinker->flags = flags;
> +
> +	if (flags & SHRINKER_MEMCG_AWARE) {
> +		err = prealloc_memcg_shrinker(shrinker);
> +		if (err == -ENOSYS)
> +			shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
> +		else if (err == 0)
> +			goto done;
> +		else
> +			goto err_flags;
> +	}
> +
> +	/*
> +	 * The nr_deferred is available on per memcg level for memcg aware
> +	 * shrinkers, so only allocate nr_deferred in the following cases:
> +	 *  - non memcg aware shrinkers
> +	 *  - !CONFIG_MEMCG
> +	 *  - memcg is disabled by kernel command line
> +	 */
> +	size = sizeof(*shrinker->nr_deferred);
> +	if (flags & SHRINKER_NUMA_AWARE)
> +		size *= nr_node_ids;
> +
> +	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
> +	if (!shrinker->nr_deferred)
> +		goto err_flags;
> +
> +done:
> +	return shrinker;
> +
> +err_flags:
> +#ifdef CONFIG_SHRINKER_DEBUG
> +	kfree_const(shrinker->name);
> +	shrinker->name = NULL;

This could be shrinker_debugfs_name_free()

> +err_name:
> +#endif
> +	kfree(shrinker);
> +	return NULL;
> +}
> +EXPORT_SYMBOL(shrinker_alloc);
> +
> +void shrinker_free_non_registered(struct shrinker *shrinker)
> +{
> +#ifdef CONFIG_SHRINKER_DEBUG
> +	kfree_const(shrinker->name);
> +	shrinker->name = NULL;

This could be shrinker_debugfs_name_free()

> +#endif
> +	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
> +		down_write(&shrinker_rwsem);
> +		unregister_memcg_shrinker(shrinker);
> +		up_write(&shrinker_rwsem);
> +	}
> +
> +	kfree(shrinker->nr_deferred);
> +	shrinker->nr_deferred = NULL;
> +
> +	kfree(shrinker);
> +}
> +EXPORT_SYMBOL(shrinker_free_non_registered);
> +
> +void shrinker_register(struct shrinker *shrinker)
> +{
> +	down_write(&shrinker_rwsem);
> +	list_add_tail(&shrinker->list, &shrinker_list);
> +	shrinker->flags |= SHRINKER_REGISTERED;
> +	shrinker_debugfs_add(shrinker);
> +	up_write(&shrinker_rwsem);
> +}
> +EXPORT_SYMBOL(shrinker_register);
> +
> +void shrinker_unregister(struct shrinker *shrinker)

You have made all shrinkers to be dynamically allocated, so
we should prevent users from allocating shrinkers statically and
use this function to unregister it. It is better to add a
flag like SHRINKER_ALLOCATED which is set in shrinker_alloc(),
and check whether it is set in shrinker_unregister(), if not
maybe a warning should be added to tell the users what happened.

> +{
> +	struct dentry *debugfs_entry;
> +	int debugfs_id;
> +
> +	if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))
> +		return;
> +
> +	down_write(&shrinker_rwsem);
> +	list_del(&shrinker->list);
> +	shrinker->flags &= ~SHRINKER_REGISTERED;
> +	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> +		unregister_memcg_shrinker(shrinker);
> +	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);

In the internal of this function, you also could use
shrinker_debugfs_name_free().

Thanks.

> +	up_write(&shrinker_rwsem);
> +
> +	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
> +
> +	kfree(shrinker->nr_deferred);
> +	shrinker->nr_deferred = NULL;
> +
> +	kfree(shrinker);
> +}
> +EXPORT_SYMBOL(shrinker_unregister);
> +
>   /*
>    * Add a shrinker callback to be called from the vm.
>    */

Re: [PATCH v2 04/47] kvm: mmu: dynamically allocate the x86-mmu shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the x86-mmu shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.

Re: [PATCH v2 06/47] drm/ttm: dynamically allocate the drm-ttm_pool shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the drm-ttm_pool shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.

Re: [PATCH v2 07/47] xenbus/backend: dynamically allocate the xen-backend shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the xen-backend shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.

Re: [PATCH v2 08/47] erofs: dynamically allocate the erofs-shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the erofs-shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.

Re: [PATCH v2 09/47] f2fs: dynamically allocate the f2fs-shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the f2fs-shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.

Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Qi Zheng]

Hi Muchun,

On 2023/7/25 17:02, Muchun Song wrote:
> 
> 
> On 2023/7/24 17:43, Qi Zheng wrote:
>> Currently, the shrinker instances can be divided into the following three
>> types:
>>
>> a) global shrinker instance statically defined in the kernel, such as
>>     workingset_shadow_shrinker.
>>
>> b) global shrinker instance statically defined in the kernel modules, 
>> such
>>     as mmu_shrinker in x86.
>>
>> c) shrinker instance embedded in other structures.
>>
>> For case a, the memory of shrinker instance is never freed. For case b,
>> the memory of shrinker instance will be freed after synchronize_rcu() 
>> when
>> the module is unloaded. For case c, the memory of shrinker instance will
>> be freed along with the structure it is embedded in.
>>
>> In preparation for implementing lockless slab shrink, we need to
>> dynamically allocate those shrinker instances in case c, then the memory
>> can be dynamically freed alone by calling kfree_rcu().
>>
>> So this commit adds the following new APIs for dynamically allocating
>> shrinker, and add a private_data field to struct shrinker to record and
>> get the original embedded structure.
>>
>> 1. shrinker_alloc()
>>
>> Used to allocate shrinker instance itself and related memory, it will
>> return a pointer to the shrinker instance on success and NULL on failure.
>>
>> 2. shrinker_free_non_registered()
>>
>> Used to destroy the non-registered shrinker instance.
> 
> At least I don't like this name. I know you want to tell others
> this function only should be called when shrinker has not been
> registed but allocated. Maybe shrinker_free() is more simple.
> And and a comment to tell the users when to use it.

OK, if no one else objects, I will change it to shrinker_free() in
the next version.

> 
>>
>> 3. shrinker_register()
>>
>> Used to register the shrinker instance, which is same as the current
>> register_shrinker_prepared().
>>
>> 4. shrinker_unregister()
>>
>> Used to unregister and free the shrinker instance.
>>
>> In order to simplify shrinker-related APIs and make shrinker more
>> independent of other kernel mechanisms, subsequent submissions will use
>> the above API to convert all shrinkers (including case a and b) to
>> dynamically allocated, and then remove all existing APIs.
>>
>> This will also have another advantage mentioned by Dave Chinner:
>>
>> ```
>> The other advantage of this is that it will break all the existing
>> out of tree code and third party modules using the old API and will
>> no longer work with a kernel using lockless slab shrinkers. They
>> need to break (both at the source and binary levels) to stop bad
>> things from happening due to using uncoverted shrinkers in the new
>> setup.
>> ```
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   include/linux/shrinker.h |   6 +++
>>   mm/shrinker.c            | 113 +++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 119 insertions(+)
>>
>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
>> index 961cb84e51f5..296f5e163861 100644
>> --- a/include/linux/shrinker.h
>> +++ b/include/linux/shrinker.h
>> @@ -70,6 +70,8 @@ struct shrinker {
>>       int seeks;    /* seeks to recreate an obj */
>>       unsigned flags;
>> +    void *private_data;
>> +
>>       /* These are for internal use */
>>       struct list_head list;
>>   #ifdef CONFIG_MEMCG
>> @@ -98,6 +100,10 @@ struct shrinker {
>>   unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup 
>> *memcg,
>>                 int priority);
>> +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, 
>> ...);
>> +void shrinker_free_non_registered(struct shrinker *shrinker);
>> +void shrinker_register(struct shrinker *shrinker);
>> +void shrinker_unregister(struct shrinker *shrinker);
>>   extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
>>                           const char *fmt, ...);
>> diff --git a/mm/shrinker.c b/mm/shrinker.c
>> index 0a32ef42f2a7..d820e4cc5806 100644
>> --- a/mm/shrinker.c
>> +++ b/mm/shrinker.c
>> @@ -548,6 +548,119 @@ unsigned long shrink_slab(gfp_t gfp_mask, int 
>> nid, struct mem_cgroup *memcg,
>>       return freed;
>>   }
>> +struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, 
>> ...)
>> +{
>> +    struct shrinker *shrinker;
>> +    unsigned int size;
>> +    va_list __maybe_unused ap;
>> +    int err;
>> +
>> +    shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL);
>> +    if (!shrinker)
>> +        return NULL;
>> +
>> +#ifdef CONFIG_SHRINKER_DEBUG
>> +    va_start(ap, fmt);
>> +    shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
>> +    va_end(ap);
>> +    if (!shrinker->name)
>> +        goto err_name;
>> +#endif
> 
> So why not introduce another helper to handle this and declare it
> as a void function when !CONFIG_SHRINKER_DEBUG? Something like the
> following:
> 
> #ifdef CONFIG_SHRINKER_DEBUG
> static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const 
> char *fmt,
>                                         va_list vargs)
> 
> {
>      shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, vargs);
>      return shrinker->name ? 0 : -ENOMEM;
> }
> #else
> static int shrinker_debugfs_name_alloc(struct shrinker *shrinker, const 
> char *fmt,
>                                         va_list vargs)
> {
>      return 0;
> }
> #endif

Will do in the next version.

> 
>> +    shrinker->flags = flags;
>> +
>> +    if (flags & SHRINKER_MEMCG_AWARE) {
>> +        err = prealloc_memcg_shrinker(shrinker);
>> +        if (err == -ENOSYS)
>> +            shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
>> +        else if (err == 0)
>> +            goto done;
>> +        else
>> +            goto err_flags;
>> +    }
>> +
>> +    /*
>> +     * The nr_deferred is available on per memcg level for memcg aware
>> +     * shrinkers, so only allocate nr_deferred in the following cases:
>> +     *  - non memcg aware shrinkers
>> +     *  - !CONFIG_MEMCG
>> +     *  - memcg is disabled by kernel command line
>> +     */
>> +    size = sizeof(*shrinker->nr_deferred);
>> +    if (flags & SHRINKER_NUMA_AWARE)
>> +        size *= nr_node_ids;
>> +
>> +    shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
>> +    if (!shrinker->nr_deferred)
>> +        goto err_flags;
>> +
>> +done:
>> +    return shrinker;
>> +
>> +err_flags:
>> +#ifdef CONFIG_SHRINKER_DEBUG
>> +    kfree_const(shrinker->name);
>> +    shrinker->name = NULL;
> 
> This could be shrinker_debugfs_name_free()

Will do.

> 
>> +err_name:
>> +#endif
>> +    kfree(shrinker);
>> +    return NULL;
>> +}
>> +EXPORT_SYMBOL(shrinker_alloc);
>> +
>> +void shrinker_free_non_registered(struct shrinker *shrinker)
>> +{
>> +#ifdef CONFIG_SHRINKER_DEBUG
>> +    kfree_const(shrinker->name);
>> +    shrinker->name = NULL;
> 
> This could be shrinker_debugfs_name_free()
> 
>> +#endif
>> +    if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
>> +        down_write(&shrinker_rwsem);
>> +        unregister_memcg_shrinker(shrinker);
>> +        up_write(&shrinker_rwsem);
>> +    }
>> +
>> +    kfree(shrinker->nr_deferred);
>> +    shrinker->nr_deferred = NULL;
>> +
>> +    kfree(shrinker);
>> +}
>> +EXPORT_SYMBOL(shrinker_free_non_registered);
>> +
>> +void shrinker_register(struct shrinker *shrinker)
>> +{
>> +    down_write(&shrinker_rwsem);
>> +    list_add_tail(&shrinker->list, &shrinker_list);
>> +    shrinker->flags |= SHRINKER_REGISTERED;
>> +    shrinker_debugfs_add(shrinker);
>> +    up_write(&shrinker_rwsem);
>> +}
>> +EXPORT_SYMBOL(shrinker_register);
>> +
>> +void shrinker_unregister(struct shrinker *shrinker)
> 
> You have made all shrinkers to be dynamically allocated, so
> we should prevent users from allocating shrinkers statically and
> use this function to unregister it. It is better to add a
> flag like SHRINKER_ALLOCATED which is set in shrinker_alloc(),
> and check whether it is set in shrinker_unregister(), if not
> maybe a warning should be added to tell the users what happened.

Make sense, will do.

> 
>> +{
>> +    struct dentry *debugfs_entry;
>> +    int debugfs_id;
>> +
>> +    if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))
>> +        return;
>> +
>> +    down_write(&shrinker_rwsem);
>> +    list_del(&shrinker->list);
>> +    shrinker->flags &= ~SHRINKER_REGISTERED;
>> +    if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>> +        unregister_memcg_shrinker(shrinker);
>> +    debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
> 
> In the internal of this function, you also could use
> shrinker_debugfs_name_free().

Yeah, will do.

Thanks,
Qi

> 
> Thanks.
> 
>> +    up_write(&shrinker_rwsem);
>> +
>> +    shrinker_debugfs_remove(debugfs_entry, debugfs_id);
>> +
>> +    kfree(shrinker->nr_deferred);
>> +    shrinker->nr_deferred = NULL;
>> +
>> +    kfree(shrinker);
>> +}
>> +EXPORT_SYMBOL(shrinker_unregister);
>> +
>>   /*
>>    * Add a shrinker callback to be called from the vm.
>>    */
> 

Re: [PATCH v2 10/47] gfs2: dynamically allocate the gfs2-glock shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the gfs2-glock shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.

Re: [PATCH v2 11/47] gfs2: dynamically allocate the gfs2-qd shrinker

[Muchun Song]

On 2023/7/24 17:43, Qi Zheng wrote:
> Use new APIs to dynamically allocate the gfs2-qd shrinker.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>   fs/gfs2/main.c  |  6 +++---
>   fs/gfs2/quota.c | 26 ++++++++++++++++++++------
>   fs/gfs2/quota.h |  3 ++-
>   3 files changed, 25 insertions(+), 10 deletions(-)
>
> diff --git a/fs/gfs2/main.c b/fs/gfs2/main.c
> index afcb32854f14..e47b1cc79f59 100644
> --- a/fs/gfs2/main.c
> +++ b/fs/gfs2/main.c
> @@ -147,7 +147,7 @@ static int __init init_gfs2_fs(void)
>   	if (!gfs2_trans_cachep)
>   		goto fail_cachep8;
>   
> -	error = register_shrinker(&gfs2_qd_shrinker, "gfs2-qd");
> +	error = gfs2_qd_shrinker_init();
>   	if (error)
>   		goto fail_shrinker;
>   
> @@ -196,7 +196,7 @@ static int __init init_gfs2_fs(void)
>   fail_wq2:
>   	destroy_workqueue(gfs_recovery_wq);
>   fail_wq1:
> -	unregister_shrinker(&gfs2_qd_shrinker);
> +	gfs2_qd_shrinker_exit();
>   fail_shrinker:
>   	kmem_cache_destroy(gfs2_trans_cachep);
>   fail_cachep8:
> @@ -229,7 +229,7 @@ static int __init init_gfs2_fs(void)
>   
>   static void __exit exit_gfs2_fs(void)
>   {
> -	unregister_shrinker(&gfs2_qd_shrinker);
> +	gfs2_qd_shrinker_exit();
>   	gfs2_glock_exit();
>   	gfs2_unregister_debugfs();
>   	unregister_filesystem(&gfs2_fs_type);
> diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> index 704192b73605..bc9883cea847 100644
> --- a/fs/gfs2/quota.c
> +++ b/fs/gfs2/quota.c
> @@ -186,13 +186,27 @@ static unsigned long gfs2_qd_shrink_count(struct shrinker *shrink,
>   	return vfs_pressure_ratio(list_lru_shrink_count(&gfs2_qd_lru, sc));
>   }
>   
> -struct shrinker gfs2_qd_shrinker = {
> -	.count_objects = gfs2_qd_shrink_count,
> -	.scan_objects = gfs2_qd_shrink_scan,
> -	.seeks = DEFAULT_SEEKS,
> -	.flags = SHRINKER_NUMA_AWARE,
> -};
> +static struct shrinker *gfs2_qd_shrinker;
> +
> +int gfs2_qd_shrinker_init(void)

It's better to declare this as __init.

> +{
> +	gfs2_qd_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE, "gfs2-qd");
> +	if (!gfs2_qd_shrinker)
> +		return -ENOMEM;
> +
> +	gfs2_qd_shrinker->count_objects = gfs2_qd_shrink_count;
> +	gfs2_qd_shrinker->scan_objects = gfs2_qd_shrink_scan;
> +	gfs2_qd_shrinker->seeks = DEFAULT_SEEKS;
> +
> +	shrinker_register(gfs2_qd_shrinker);
>   
> +	return 0;
> +}
> +
> +void gfs2_qd_shrinker_exit(void)
> +{
> +	shrinker_unregister(gfs2_qd_shrinker);
> +}
>   
>   static u64 qd2index(struct gfs2_quota_data *qd)
>   {
> diff --git a/fs/gfs2/quota.h b/fs/gfs2/quota.h
> index 21ada332d555..f9cb863373f7 100644
> --- a/fs/gfs2/quota.h
> +++ b/fs/gfs2/quota.h
> @@ -59,7 +59,8 @@ static inline int gfs2_quota_lock_check(struct gfs2_inode *ip,
>   }
>   
>   extern const struct quotactl_ops gfs2_quotactl_ops;
> -extern struct shrinker gfs2_qd_shrinker;
> +int gfs2_qd_shrinker_init(void);
> +void gfs2_qd_shrinker_exit(void);
>   extern struct list_lru gfs2_qd_lru;
>   extern void __init gfs2_quota_hash_init(void);
>   

Re: [PATCH v2 12/47] NFSv4.2: dynamically allocate the nfs-xattr shrinkers

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the nfs-xattr shrinkers.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 13/47] nfs: dynamically allocate the nfs-acl shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the nfs-acl shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 14/47] nfsd: dynamically allocate the nfsd-filecache shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the nfsd-filecache shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 15/47] quota: dynamically allocate the dquota-cache shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the dquota-cache shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 16/47] ubifs: dynamically allocate the ubifs-slab shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the ubifs-slab shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 17/47] rcu: dynamically allocate the rcu-lazy shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the rcu-lazy shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
> kernel/rcu/tree_nocb.h | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index 43229d2b0c44..919f17561733 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -1397,12 +1397,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> return count ? count : SHRINK_STOP;
> }
> 
> -static struct shrinker lazy_rcu_shrinker = {
> -	.count_objects = lazy_rcu_shrink_count,
> -	.scan_objects = lazy_rcu_shrink_scan,
> -	.batch = 0,
> -	.seeks = DEFAULT_SEEKS,
> -};
> +static struct shrinker *lazy_rcu_shrinker;

Seems there is no users of this variable, maybe we could drop
this.

Re: [PATCH v2 18/47] rcu: dynamically allocate the rcu-kfree shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the rcu-kfree shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
> kernel/rcu/tree.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 1449cb69a0e0..d068ce3567fc 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3445,12 +3445,7 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> return freed == 0 ? SHRINK_STOP : freed;
> }
> 
> -static struct shrinker kfree_rcu_shrinker = {
> -	.count_objects = kfree_rcu_shrink_count,
> -	.scan_objects = kfree_rcu_shrink_scan,
> -	.batch = 0,
> -	.seeks = DEFAULT_SEEKS,
> -};
> +static struct shrinker *kfree_rcu_shrinker;

Same as patch #17.

Re: [PATCH v2 19/47] mm: thp: dynamically allocate the thp-related shrinkers

[Muchun Song]

On 2023/7/24 17:43, Qi Zheng wrote:
> Use new APIs to dynamically allocate the thp-zero and thp-deferred_split
> shrinkers.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>   mm/huge_memory.c | 69 +++++++++++++++++++++++++++++++-----------------
>   1 file changed, 45 insertions(+), 24 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8c94b34024a2..4db5a1834d81 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -65,7 +65,11 @@ unsigned long transparent_hugepage_flags __read_mostly =
>   	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
>   	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
>   
> -static struct shrinker deferred_split_shrinker;
> +static struct shrinker *deferred_split_shrinker;
> +static unsigned long deferred_split_count(struct shrinker *shrink,
> +					  struct shrink_control *sc);
> +static unsigned long deferred_split_scan(struct shrinker *shrink,
> +					 struct shrink_control *sc);
>   
>   static atomic_t huge_zero_refcount;
>   struct page *huge_zero_page __read_mostly;
> @@ -229,11 +233,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
>   	return 0;
>   }
>   
> -static struct shrinker huge_zero_page_shrinker = {
> -	.count_objects = shrink_huge_zero_page_count,
> -	.scan_objects = shrink_huge_zero_page_scan,
> -	.seeks = DEFAULT_SEEKS,
> -};
> +static struct shrinker *huge_zero_page_shrinker;

Same as patch #17.

>   
>   #ifdef CONFIG_SYSFS
>   static ssize_t enabled_show(struct kobject *kobj,
> @@ -454,6 +454,40 @@ static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
>   }
>   #endif /* CONFIG_SYSFS */
>   
> +static int thp_shrinker_init(void)

Better to declare it as __init.

> +{
> +	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
> +	if (!huge_zero_page_shrinker)
> +		return -ENOMEM;
> +
> +	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
> +						 SHRINKER_MEMCG_AWARE |
> +						 SHRINKER_NONSLAB,
> +						 "thp-deferred_split");
> +	if (!deferred_split_shrinker) {
> +		shrinker_free_non_registered(huge_zero_page_shrinker);
> +		return -ENOMEM;
> +	}
> +
> +	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
> +	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
> +	huge_zero_page_shrinker->seeks = DEFAULT_SEEKS;
> +	shrinker_register(huge_zero_page_shrinker);
> +
> +	deferred_split_shrinker->count_objects = deferred_split_count;
> +	deferred_split_shrinker->scan_objects = deferred_split_scan;
> +	deferred_split_shrinker->seeks = DEFAULT_SEEKS;
> +	shrinker_register(deferred_split_shrinker);
> +
> +	return 0;
> +}
> +
> +static void thp_shrinker_exit(void)

Same as here.

> +{
> +	shrinker_unregister(huge_zero_page_shrinker);
> +	shrinker_unregister(deferred_split_shrinker);
> +}
> +
>   static int __init hugepage_init(void)
>   {
>   	int err;
> @@ -482,12 +516,9 @@ static int __init hugepage_init(void)
>   	if (err)
>   		goto err_slab;
>   
> -	err = register_shrinker(&huge_zero_page_shrinker, "thp-zero");
> -	if (err)
> -		goto err_hzp_shrinker;
> -	err = register_shrinker(&deferred_split_shrinker, "thp-deferred_split");
> +	err = thp_shrinker_init();
>   	if (err)
> -		goto err_split_shrinker;
> +		goto err_shrinker;
>   
>   	/*
>   	 * By default disable transparent hugepages on smaller systems,
> @@ -505,10 +536,8 @@ static int __init hugepage_init(void)
>   
>   	return 0;
>   err_khugepaged:
> -	unregister_shrinker(&deferred_split_shrinker);
> -err_split_shrinker:
> -	unregister_shrinker(&huge_zero_page_shrinker);
> -err_hzp_shrinker:
> +	thp_shrinker_exit();
> +err_shrinker:
>   	khugepaged_destroy();
>   err_slab:
>   	hugepage_exit_sysfs(hugepage_kobj);
> @@ -2851,7 +2880,7 @@ void deferred_split_folio(struct folio *folio)
>   #ifdef CONFIG_MEMCG
>   		if (memcg)
>   			set_shrinker_bit(memcg, folio_nid(folio),
> -					 deferred_split_shrinker.id);
> +					 deferred_split_shrinker->id);
>   #endif
>   	}
>   	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
> @@ -2925,14 +2954,6 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>   	return split;
>   }
>   
> -static struct shrinker deferred_split_shrinker = {
> -	.count_objects = deferred_split_count,
> -	.scan_objects = deferred_split_scan,
> -	.seeks = DEFAULT_SEEKS,
> -	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE |
> -		 SHRINKER_NONSLAB,
> -};
> -
>   #ifdef CONFIG_DEBUG_FS
>   static void split_huge_pages_all(void)
>   {

Re: [PATCH v2 20/47] sunrpc: dynamically allocate the sunrpc_cred shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the sunrpc_cred shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 21/47] mm: workingset: dynamically allocate the mm-shadow shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Use new APIs to dynamically allocate the mm-shadow shrinker.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
> mm/workingset.c | 26 ++++++++++++++------------
> 1 file changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/workingset.c b/mm/workingset.c
> index 4686ae363000..4bc85f739b13 100644
> --- a/mm/workingset.c
> +++ b/mm/workingset.c
> @@ -762,12 +762,7 @@ static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
> NULL);
> }
> 
> -static struct shrinker workingset_shadow_shrinker = {
> -	.count_objects = count_shadow_nodes,
> -	.scan_objects = scan_shadow_nodes,
> -	.seeks = 0, /* ->count reports only fully expendable nodes */
> -	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
> -};
> +static struct shrinker *workingset_shadow_shrinker;


Same as patch #17.

Re: [PATCH v2 22/47] drm/i915: dynamically allocate the i915_gem_mm shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the i915_gem_mm shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct drm_i915_private.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 23/47] drm/msm: dynamically allocate the drm-msm_gem shrinker

[Muchun Song]

On 2023/7/24 17:43, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the drm-msm_gem shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct msm_drm_private.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

A nit bellow.

> ---
>   drivers/gpu/drm/msm/msm_drv.c          |  4 ++-
>   drivers/gpu/drm/msm/msm_drv.h          |  4 +--
>   drivers/gpu/drm/msm/msm_gem_shrinker.c | 36 ++++++++++++++++----------
>   3 files changed, 28 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 891eff8433a9..7f6933be703f 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -461,7 +461,9 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)
>   	if (ret)
>   		goto err_msm_uninit;
>   
> -	msm_gem_shrinker_init(ddev);
> +	ret = msm_gem_shrinker_init(ddev);
> +	if (ret)
> +		goto err_msm_uninit;
>   
>   	if (priv->kms_init) {
>   		ret = priv->kms_init(ddev);
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index e13a8cbd61c9..84523d4a1e58 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -217,7 +217,7 @@ struct msm_drm_private {
>   	} vram;
>   
>   	struct notifier_block vmap_notifier;
> -	struct shrinker shrinker;
> +	struct shrinker *shrinker;
>   
>   	struct drm_atomic_state *pm_state;
>   
> @@ -279,7 +279,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
>   unsigned long msm_gem_shrinker_shrink(struct drm_device *dev, unsigned long nr_to_scan);
>   #endif
>   
> -void msm_gem_shrinker_init(struct drm_device *dev);
> +int msm_gem_shrinker_init(struct drm_device *dev);
>   void msm_gem_shrinker_cleanup(struct drm_device *dev);
>   
>   int msm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
> diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> index f38296ad8743..7daab1298c11 100644
> --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
> +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> @@ -34,8 +34,7 @@ static bool can_block(struct shrink_control *sc)
>   static unsigned long
>   msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
>   {
> -	struct msm_drm_private *priv =
> -		container_of(shrinker, struct msm_drm_private, shrinker);
> +	struct msm_drm_private *priv = shrinker->private_data;
>   	unsigned count = priv->lru.dontneed.count;
>   
>   	if (can_swap())
> @@ -100,8 +99,7 @@ active_evict(struct drm_gem_object *obj)
>   static unsigned long
>   msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>   {
> -	struct msm_drm_private *priv =
> -		container_of(shrinker, struct msm_drm_private, shrinker);
> +	struct msm_drm_private *priv = shrinker->private_data;
>   	struct {
>   		struct drm_gem_lru *lru;
>   		bool (*shrink)(struct drm_gem_object *obj);
> @@ -148,10 +146,11 @@ msm_gem_shrinker_shrink(struct drm_device *dev, unsigned long nr_to_scan)
>   	struct shrink_control sc = {
>   		.nr_to_scan = nr_to_scan,
>   	};
> -	int ret;
> +	unsigned long ret = SHRINK_STOP;
>   
>   	fs_reclaim_acquire(GFP_KERNEL);
> -	ret = msm_gem_shrinker_scan(&priv->shrinker, &sc);
> +	if (priv->shrinker)
> +		ret = msm_gem_shrinker_scan(priv->shrinker, &sc);
>   	fs_reclaim_release(GFP_KERNEL);
>   
>   	return ret;
> @@ -210,16 +209,27 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
>    *
>    * This function registers and sets up the msm shrinker.
>    */
> -void msm_gem_shrinker_init(struct drm_device *dev)
> +int msm_gem_shrinker_init(struct drm_device *dev)
>   {
>   	struct msm_drm_private *priv = dev->dev_private;
> -	priv->shrinker.count_objects = msm_gem_shrinker_count;
> -	priv->shrinker.scan_objects = msm_gem_shrinker_scan;
> -	priv->shrinker.seeks = DEFAULT_SEEKS;
> -	WARN_ON(register_shrinker(&priv->shrinker, "drm-msm_gem"));
> +
> +	priv->shrinker = shrinker_alloc(0, "drm-msm_gem");
> +	if (!priv->shrinker) {

Just "if (WARN_ON(!priv->shrinker))"

> +		WARN_ON(1);
> +		return -ENOMEM;
> +	}
> +
> +	priv->shrinker->count_objects = msm_gem_shrinker_count;
> +	priv->shrinker->scan_objects = msm_gem_shrinker_scan;
> +	priv->shrinker->seeks = DEFAULT_SEEKS;
> +	priv->shrinker->private_data = priv;
> +
> +	shrinker_register(priv->shrinker);
>   
>   	priv->vmap_notifier.notifier_call = msm_gem_shrinker_vmap;
>   	WARN_ON(register_vmap_purge_notifier(&priv->vmap_notifier));
> +
> +	return 0;
>   }
>   
>   /**
> @@ -232,8 +242,8 @@ void msm_gem_shrinker_cleanup(struct drm_device *dev)
>   {
>   	struct msm_drm_private *priv = dev->dev_private;
>   
> -	if (priv->shrinker.nr_deferred) {
> +	if (priv->shrinker) {
>   		WARN_ON(unregister_vmap_purge_notifier(&priv->vmap_notifier));
> -		unregister_shrinker(&priv->shrinker);
> +		shrinker_unregister(priv->shrinker);
>   	}
>   }

Re: [PATCH v2 25/47] dm: dynamically allocate the dm-bufio shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the dm-bufio shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct dm_bufio_client.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 26/47] dm zoned: dynamically allocate the dm-zoned-meta shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the dm-zoned-meta shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct dmz_metadata.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Dave Chinner]

On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote:
> Currently, the shrinker instances can be divided into the following three
> types:
> 
> a) global shrinker instance statically defined in the kernel, such as
>    workingset_shadow_shrinker.
> 
> b) global shrinker instance statically defined in the kernel modules, such
>    as mmu_shrinker in x86.
> 
> c) shrinker instance embedded in other structures.
> 
> For case a, the memory of shrinker instance is never freed. For case b,
> the memory of shrinker instance will be freed after synchronize_rcu() when
> the module is unloaded. For case c, the memory of shrinker instance will
> be freed along with the structure it is embedded in.
> 
> In preparation for implementing lockless slab shrink, we need to
> dynamically allocate those shrinker instances in case c, then the memory
> can be dynamically freed alone by calling kfree_rcu().
> 
> So this commit adds the following new APIs for dynamically allocating
> shrinker, and add a private_data field to struct shrinker to record and
> get the original embedded structure.
> 
> 1. shrinker_alloc()
> 
> Used to allocate shrinker instance itself and related memory, it will
> return a pointer to the shrinker instance on success and NULL on failure.
> 
> 2. shrinker_free_non_registered()
> 
> Used to destroy the non-registered shrinker instance.

This is a bit nasty

> 
> 3. shrinker_register()
> 
> Used to register the shrinker instance, which is same as the current
> register_shrinker_prepared().
> 
> 4. shrinker_unregister()

rename this "shrinker_free()" and key the two different freeing
cases on the SHRINKER_REGISTERED bit rather than mostly duplicating
the two.

void shrinker_free(struct shrinker *shrinker)
{
	struct dentry *debugfs_entry = NULL;
	int debugfs_id;

	if (!shrinker)
		return;

	down_write(&shrinker_rwsem);
	if (shrinker->flags & SHRINKER_REGISTERED) {
		list_del(&shrinker->list);
		debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
	} else if (IS_ENABLED(CONFIG_SHRINKER_DEBUG)) {
		kfree_const(shrinker->name);
	}

	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
		unregister_memcg_shrinker(shrinker);
	up_write(&shrinker_rwsem);

	if (debugfs_entry)
		shrinker_debugfs_remove(debugfs_entry, debugfs_id);

	kfree(shrinker->nr_deferred);
	kfree(shrinker);
}
EXPORT_SYMBOL_GPL(shrinker_free);

-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH v2 27/47] md/raid5: dynamically allocate the md-raid5 shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the md-raid5 shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct r5conf.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 28/47] bcache: dynamically allocate the md-bcache shrinker

[Muchun Song]

On 2023/7/24 17:43, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the md-bcache shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct cache_set.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>   drivers/md/bcache/bcache.h |  2 +-
>   drivers/md/bcache/btree.c  | 27 ++++++++++++++++-----------
>   drivers/md/bcache/sysfs.c  |  3 ++-
>   3 files changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 5a79bb3c272f..c622bc50f81b 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -541,7 +541,7 @@ struct cache_set {
>   	struct bio_set		bio_split;
>   
>   	/* For the btree cache */
> -	struct shrinker		shrink;
> +	struct shrinker		*shrink;
>   
>   	/* For the btree cache and anything allocation related */
>   	struct mutex		bucket_lock;
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index fd121a61f17c..c176c7fc77d9 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -667,7 +667,7 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush)
>   static unsigned long bch_mca_scan(struct shrinker *shrink,
>   				  struct shrink_control *sc)
>   {
> -	struct cache_set *c = container_of(shrink, struct cache_set, shrink);
> +	struct cache_set *c = shrink->private_data;
>   	struct btree *b, *t;
>   	unsigned long i, nr = sc->nr_to_scan;
>   	unsigned long freed = 0;
> @@ -734,7 +734,7 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
>   static unsigned long bch_mca_count(struct shrinker *shrink,
>   				   struct shrink_control *sc)
>   {
> -	struct cache_set *c = container_of(shrink, struct cache_set, shrink);
> +	struct cache_set *c = shrink->private_data;
>   
>   	if (c->shrinker_disabled)
>   		return 0;
> @@ -752,8 +752,8 @@ void bch_btree_cache_free(struct cache_set *c)
>   
>   	closure_init_stack(&cl);
>   
> -	if (c->shrink.list.next)
> -		unregister_shrinker(&c->shrink);
> +	if (c->shrink)
> +		shrinker_unregister(c->shrink);
>   
>   	mutex_lock(&c->bucket_lock);
>   
> @@ -828,14 +828,19 @@ int bch_btree_cache_alloc(struct cache_set *c)
>   		c->verify_data = NULL;
>   #endif
>   
> -	c->shrink.count_objects = bch_mca_count;
> -	c->shrink.scan_objects = bch_mca_scan;
> -	c->shrink.seeks = 4;
> -	c->shrink.batch = c->btree_pages * 2;
> +	c->shrink = shrinker_alloc(0, "md-bcache:%pU", c->set_uuid);
> +	if (!c->shrink) {
> +		pr_warn("bcache: %s: could not allocate shrinker\n", __func__);
> +		return -ENOMEM;

Seems you have cheanged the semantic of this. In the past,
it is better to have a shrinker, but now it becomes a mandatory.
Right? I don't know if it is acceptable. From my point of view,
just do the cleanup, don't change any behaviour.

> +	}
> +
> +	c->shrink->count_objects = bch_mca_count;
> +	c->shrink->scan_objects = bch_mca_scan;
> +	c->shrink->seeks = 4;
> +	c->shrink->batch = c->btree_pages * 2;
> +	c->shrink->private_data = c;
>   
> -	if (register_shrinker(&c->shrink, "md-bcache:%pU", c->set_uuid))
> -		pr_warn("bcache: %s: could not register shrinker\n",
> -				__func__);
> +	shrinker_register(c->shrink);
>   
>   	return 0;
>   }
> diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
> index 0e2c1880f60b..45d8af755de6 100644
> --- a/drivers/md/bcache/sysfs.c
> +++ b/drivers/md/bcache/sysfs.c
> @@ -866,7 +866,8 @@ STORE(__bch_cache_set)
>   
>   		sc.gfp_mask = GFP_KERNEL;
>   		sc.nr_to_scan = strtoul_or_return(buf);
> -		c->shrink.scan_objects(&c->shrink, &sc);
> +		if (c->shrink)
> +			c->shrink->scan_objects(c->shrink, &sc);
>   	}
>   
>   	sysfs_strtoul_clamp(congested_read_threshold_us,

Re: [PATCH v2 29/47] vmw_balloon: dynamically allocate the vmw-balloon shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the vmw-balloon shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct vmballoon.
> 
> And we can simply exit vmballoon_init() when registering the shrinker
> fails. So the shrinker_registered indication is redundant, just remove it.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Nice cleanup.

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 30/47] virtio_balloon: dynamically allocate the virtio-balloon shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the virtio-balloon shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct virtio_balloon.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 31/47] mbcache: dynamically allocate the mbcache shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the mbcache shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct mb_cache.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 32/47] ext4: dynamically allocate the ext4-es shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the ext4-es shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct ext4_sb_info.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 33/47] jbd2, ext4: dynamically allocate the jbd2-journal shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the jbd2-journal shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct journal_s.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 36/47] xfs: dynamically allocate the xfs-buf shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the xfs-buf shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct xfs_buftarg.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 37/47] xfs: dynamically allocate the xfs-inodegc shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the xfs-inodegc shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct xfs_mount.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 38/47] xfs: dynamically allocate the xfs-qm shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the xfs-qm shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct xfs_quotainfo.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 39/47] zsmalloc: dynamically allocate the mm-zspool shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the mm-zspool shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct zs_pool.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 40/47] fs: super: dynamically allocate the s_shrink

[Muchun Song]

On 2023/7/24 17:43, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the s_shrink, so that it can be freed asynchronously
> using kfree_rcu(). Then it doesn't need to wait for RCU read-side critical
> section when releasing the struct super_block.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 41/47] mm: shrinker: remove old APIs

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Now no users are using the old APIs, just remove them.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 42/47] drm/ttm: introduce pool_shrink_rwsem

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Currently, the synchronize_shrinkers() is only used by TTM pool. It only
> requires that no shrinkers run in parallel.
> 
> After we use RCU+refcount method to implement the lockless slab shrink,
> we can not use shrinker_rwsem or synchronize_rcu() to guarantee that all
> shrinker invocations have seen an update before freeing memory.
> 
> So we introduce a new pool_shrink_rwsem to implement a private
> synchronize_shrinkers(), so as to achieve the same purpose.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 44/47] mm: shrinker: make global slab shrink lockless

[Dave Chinner]

On Mon, Jul 24, 2023 at 05:43:51PM +0800, Qi Zheng wrote:
> The shrinker_rwsem is a global read-write lock in shrinkers subsystem,
> which protects most operations such as slab shrink, registration and
> unregistration of shrinkers, etc. This can easily cause problems in the
> following cases.
> 
> 1) When the memory pressure is high and there are many filesystems
>    mounted or unmounted at the same time, slab shrink will be affected
>    (down_read_trylock() failed).
> 
>    Such as the real workload mentioned by Kirill Tkhai:
> 
>    ```
>    One of the real workloads from my experience is start
>    of an overcommitted node containing many starting
>    containers after node crash (or many resuming containers
>    after reboot for kernel update). In these cases memory
>    pressure is huge, and the node goes round in long reclaim.
>    ```
> 
> 2) If a shrinker is blocked (such as the case mentioned
>    in [1]) and a writer comes in (such as mount a fs),
>    then this writer will be blocked and cause all
>    subsequent shrinker-related operations to be blocked.
> 
> Even if there is no competitor when shrinking slab, there may still be a
> problem. The down_read_trylock() may become a perf hotspot with frequent
> calls to shrink_slab(). Because of the poor multicore scalability of
> atomic operations, this can lead to a significant drop in IPC
> (instructions per cycle).
> 
> We used to implement the lockless slab shrink with SRCU [2], but then
> kernel test robot reported -88.8% regression in
> stress-ng.ramfs.ops_per_sec test case [3], so we reverted it [4].
> 
> This commit uses the refcount+RCU method [5] proposed by Dave Chinner
> to re-implement the lockless global slab shrink. The memcg slab shrink is
> handled in the subsequent patch.
> 
> For now, all shrinker instances are converted to dynamically allocated and
> will be freed by kfree_rcu(). So we can use rcu_read_{lock,unlock}() to
> ensure that the shrinker instance is valid.
> 
> And the shrinker instance will not be run again after unregistration. So
> the structure that records the pointer of shrinker instance can be safely
> freed without waiting for the RCU read-side critical section.
> 
> In this way, while we implement the lockless slab shrink, we don't need to
> be blocked in unregister_shrinker().
> 
> The following are the test results:
> 
> stress-ng --timeout 60 --times --verify --metrics-brief --ramfs 9 &
> 
> 1) Before applying this patchset:
> 
> setting to a 60 second run per stressor
> dispatching hogs: 9 ramfs
> stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
>                           (secs)    (secs)    (secs)   (real time) (usr+sys time)
> ramfs            735238     60.00     12.37    363.70     12253.05        1955.08
> for a 60.01s run time:
>    1440.27s available CPU time
>      12.36s user time   (  0.86%)
>     363.70s system time ( 25.25%)
>     376.06s total time  ( 26.11%)
> load average: 10.79 4.47 1.69
> passed: 9: ramfs (9)
> failed: 0
> skipped: 0
> successful run completed in 60.01s (1 min, 0.01 secs)
> 
> 2) After applying this patchset:
> 
> setting to a 60 second run per stressor
> dispatching hogs: 9 ramfs
> stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
>                           (secs)    (secs)    (secs)   (real time) (usr+sys time)
> ramfs            746677     60.00     12.22    367.75     12443.70        1965.13
> for a 60.01s run time:
>    1440.26s available CPU time
>      12.21s user time   (  0.85%)
>     367.75s system time ( 25.53%)
>     379.96s total time  ( 26.38%)
> load average: 8.37 2.48 0.86
> passed: 9: ramfs (9)
> failed: 0
> skipped: 0
> successful run completed in 60.01s (1 min, 0.01 secs)
> 
> We can see that the ops/s has hardly changed.
> 
> [1]. https://lore.kernel.org/lkml/20191129214541.3110-1-ptikhomirov@virtuozzo.com/
> [2]. https://lore.kernel.org/lkml/20230313112819.38938-1-zhengqi.arch@bytedance.com/
> [3]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/
> [4]. https://lore.kernel.org/all/20230609081518.3039120-1-qi.zheng@linux.dev/
> [5]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>  include/linux/shrinker.h | 19 +++++++---
>  mm/shrinker.c            | 75 ++++++++++++++++++++++++++--------------
>  mm/shrinker_debug.c      | 52 +++++++++++++++++++++-------
>  3 files changed, 104 insertions(+), 42 deletions(-)
> 
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index 36977a70bebb..335da93cccee 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -4,6 +4,7 @@
>  
>  #include <linux/atomic.h>
>  #include <linux/types.h>
> +#include <linux/refcount.h>
>  
>  #define SHRINKER_UNIT_BITS	BITS_PER_LONG
>  
> @@ -86,6 +87,10 @@ struct shrinker {
>  	long batch;	/* reclaim batch size, 0 = default */
>  	int seeks;	/* seeks to recreate an obj */
>  	unsigned flags;
> +	bool registered;
> +
> +	refcount_t refcount;
> +	struct rcu_head rcu;
>  
>  	void *private_data;
>  
> @@ -106,14 +111,13 @@ struct shrinker {
>  #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
>  
>  /* Flags */
> -#define SHRINKER_REGISTERED	(1 << 0)
> -#define SHRINKER_NUMA_AWARE	(1 << 1)
> -#define SHRINKER_MEMCG_AWARE	(1 << 2)
> +#define SHRINKER_NUMA_AWARE	(1 << 0)
> +#define SHRINKER_MEMCG_AWARE	(1 << 1)
>  /*
>   * It just makes sense when the shrinker is also MEMCG_AWARE for now,
>   * non-MEMCG_AWARE shrinker should not have this flag set.
>   */
> -#define SHRINKER_NONSLAB	(1 << 3)
> +#define SHRINKER_NONSLAB	(1 << 2)
>  
>  unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
>  			  int priority);
> @@ -122,6 +126,13 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
>  void shrinker_register(struct shrinker *shrinker);
>  void shrinker_unregister(struct shrinker *shrinker);
>  
> +static inline bool shrinker_try_get(struct shrinker *shrinker)
> +{
> +	return READ_ONCE(shrinker->registered) &&
> +	       refcount_inc_not_zero(&shrinker->refcount);
> +}

Why do we care about shrinker->registered here? If we don't set
the refcount to 1 until we have fully initialised everything, then
the shrinker code can key entirely off the reference count and
none of the lookup code needs to care about whether the shrinker is
registered or not.

> +void shrinker_put(struct shrinker *shrinker);
> +
>  #ifdef CONFIG_SHRINKER_DEBUG
>  extern int shrinker_debugfs_add(struct shrinker *shrinker);
>  extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
> diff --git a/mm/shrinker.c b/mm/shrinker.c
> index 8a1fe844f1a4..8e3334749552 100644
> --- a/mm/shrinker.c
> +++ b/mm/shrinker.c
> @@ -2,10 +2,13 @@
>  #include <linux/memcontrol.h>
>  #include <linux/rwsem.h>
>  #include <linux/shrinker.h>
> +#include <linux/rculist.h>
> +#include <linux/spinlock.h>
>  #include <trace/events/vmscan.h>
>  
>  LIST_HEAD(shrinker_list);
>  DECLARE_RWSEM(shrinker_rwsem);
> +DEFINE_SPINLOCK(shrinker_lock);
>  
>  #ifdef CONFIG_MEMCG
>  static int shrinker_nr_max;
> @@ -450,6 +453,18 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>  	return freed;
>  }
>  
> +void shrinker_put(struct shrinker *shrinker)
> +{
> +	if (refcount_dec_and_test(&shrinker->refcount)) {
> +		spin_lock(&shrinker_lock);
> +		list_del_rcu(&shrinker->list);
> +		spin_unlock(&shrinker_lock);
> +
> +		kfree(shrinker->nr_deferred);
> +		kfree_rcu(shrinker, rcu);
> +	}
> +}

Urk, no.

We want the shrinker_free() code to block waiting for the shrinker
reference count to go to zero, because the shrinkers can reference
structures that are associated with the path that is freeing the
shrinker.

i.e. we do not want to free the superblock of a filesystem whilst
the shrinker is still running, but the way you've done this is that
the shrinker can run whilst the structure that contains it has been
torn down.

This should use a completion, then it is always safe under
rcu_read_lock().  This also gets rid of the shrinker_lock spin lock,
which only exists because we can't take a blocking lock under
rcu_read_lock(). i.e:


void shrinker_put(struct shrinker *shrinker)
{
	if (refcount_dec_and_test(&shrinker->refcount))
		complete(&shrinker->done);
}

void shrinker_free()
{
	.....
	refcount_dec(&shrinker->refcount);
	wait_for_completion(&shrinker->done);
	/*
	 * lookups on the shrinker will now all fail as refcount has
	 * fallen to zero. We can now remove it from the lists and
	 * free it.
	 */
	down_write(shrinker_rwsem);
	list_del_rcu(&shrinker->list);
	up_write(&shrinker_rwsem);
	call_rcu(shrinker->rcu_head, shrinker_free_rcu_cb);
}

....

> @@ -686,11 +711,14 @@ EXPORT_SYMBOL(shrinker_free_non_registered);
>  
>  void shrinker_register(struct shrinker *shrinker)
>  {
> -	down_write(&shrinker_rwsem);
> -	list_add_tail(&shrinker->list, &shrinker_list);
> -	shrinker->flags |= SHRINKER_REGISTERED;
> +	refcount_set(&shrinker->refcount, 1);
> +
> +	spin_lock(&shrinker_lock);
> +	list_add_tail_rcu(&shrinker->list, &shrinker_list);
> +	spin_unlock(&shrinker_lock);
> +
>  	shrinker_debugfs_add(shrinker);
> -	up_write(&shrinker_rwsem);
> +	WRITE_ONCE(shrinker->registered, true);
>  }
>  EXPORT_SYMBOL(shrinker_register);

This just looks wrong - you are trying to use WRITE_ONCE() as a
release barrier to indicate that the shrinker is now set up fully.
That's not necessary - the refcount is an atomic and along with the
rcu locks they should provides all the barriers we need. i.e.

void shrinker_register(struct shrinker *shrinker)
{
	down_write(&shrinker_rwsem);
	list_add_tail_rcu(&shrinker->list, &shrinker_list);
	shrinker->flags |= SHRINKER_REGISTERED;
	shrinker_debugfs_add(shrinker);
	up_write(&shrinker_rwsem);

	/*
	 * now the shrinker is fully set up, take the first
	 * reference to it to indicate that lookup operations are
	 * now allowed to use it via shrinker_try_get().
	 */
	refcount_set(&shrinker->refcount, 1);
}

> diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
> index f1becfd45853..c5573066adbf 100644
> --- a/mm/shrinker_debug.c
> +++ b/mm/shrinker_debug.c
> @@ -5,6 +5,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/shrinker.h>
>  #include <linux/memcontrol.h>
> +#include <linux/rculist.h>
>  
>  /* defined in vmscan.c */
>  extern struct rw_semaphore shrinker_rwsem;
> @@ -161,17 +162,21 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>  {
>  	struct dentry *entry;
>  	char buf[128];
> -	int id;
> -
> -	lockdep_assert_held(&shrinker_rwsem);
> +	int id, ret = 0;
>  
>  	/* debugfs isn't initialized yet, add debugfs entries later. */
>  	if (!shrinker_debugfs_root)
>  		return 0;
>  
> +	down_write(&shrinker_rwsem);
> +	if (shrinker->debugfs_entry)
> +		goto fail;
> +
>  	id = ida_alloc(&shrinker_debugfs_ida, GFP_KERNEL);
> -	if (id < 0)
> -		return id;
> +	if (id < 0) {
> +		ret = id;
> +		goto fail;
> +	}
>  	shrinker->debugfs_id = id;
>  
>  	snprintf(buf, sizeof(buf), "%s-%d", shrinker->name, id);
> @@ -180,7 +185,8 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>  	entry = debugfs_create_dir(buf, shrinker_debugfs_root);
>  	if (IS_ERR(entry)) {
>  		ida_free(&shrinker_debugfs_ida, id);
> -		return PTR_ERR(entry);
> +		ret = PTR_ERR(entry);
> +		goto fail;
>  	}
>  	shrinker->debugfs_entry = entry;
>  
> @@ -188,7 +194,10 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>  			    &shrinker_debugfs_count_fops);
>  	debugfs_create_file("scan", 0220, entry, shrinker,
>  			    &shrinker_debugfs_scan_fops);
> -	return 0;
> +
> +fail:
> +	up_write(&shrinker_rwsem);
> +	return ret;
>  }
>  
>  int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
> @@ -243,6 +252,11 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
>  	shrinker->name = NULL;
>  
>  	*debugfs_id = entry ? shrinker->debugfs_id : -1;
> +	/*
> +	 * Ensure that shrinker->registered has been set to false before
> +	 * shrinker->debugfs_entry is set to NULL.
> +	 */
> +	smp_wmb();
>  	shrinker->debugfs_entry = NULL;
>  
>  	return entry;
> @@ -266,14 +280,26 @@ static int __init shrinker_debugfs_init(void)
>  	shrinker_debugfs_root = dentry;
>  
>  	/* Create debugfs entries for shrinkers registered at boot */
> -	down_write(&shrinker_rwsem);
> -	list_for_each_entry(shrinker, &shrinker_list, list)
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
> +		if (!shrinker_try_get(shrinker))
> +			continue;
> +		rcu_read_unlock();
> +
>  		if (!shrinker->debugfs_entry) {
> -			ret = shrinker_debugfs_add(shrinker);
> -			if (ret)
> -				break;
> +			/* Paired with smp_wmb() in shrinker_debugfs_detach() */
> +			smp_rmb();
> +			if (READ_ONCE(shrinker->registered))
> +				ret = shrinker_debugfs_add(shrinker);
>  		}
> -	up_write(&shrinker_rwsem);
> +
> +		rcu_read_lock();
> +		shrinker_put(shrinker);
> +
> +		if (ret)
> +			break;
> +	}
> +	rcu_read_unlock();
>  
>  	return ret;
>  }

And all this churn and complexity can go away because the
shrinker_rwsem is still used to protect shrinker_register()
entirely....

-Dave.
-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH v2 44/47] mm: shrinker: make global slab shrink lockless

[Qi Zheng]

Hi Dave,

On 2023/7/26 16:08, Dave Chinner wrote:
> On Mon, Jul 24, 2023 at 05:43:51PM +0800, Qi Zheng wrote:
>> The shrinker_rwsem is a global read-write lock in shrinkers subsystem,
>> which protects most operations such as slab shrink, registration and
>> unregistration of shrinkers, etc. This can easily cause problems in the
>> following cases.
>>
>> 1) When the memory pressure is high and there are many filesystems
>>     mounted or unmounted at the same time, slab shrink will be affected
>>     (down_read_trylock() failed).
>>
>>     Such as the real workload mentioned by Kirill Tkhai:
>>
>>     ```
>>     One of the real workloads from my experience is start
>>     of an overcommitted node containing many starting
>>     containers after node crash (or many resuming containers
>>     after reboot for kernel update). In these cases memory
>>     pressure is huge, and the node goes round in long reclaim.
>>     ```
>>
>> 2) If a shrinker is blocked (such as the case mentioned
>>     in [1]) and a writer comes in (such as mount a fs),
>>     then this writer will be blocked and cause all
>>     subsequent shrinker-related operations to be blocked.
>>
>> Even if there is no competitor when shrinking slab, there may still be a
>> problem. The down_read_trylock() may become a perf hotspot with frequent
>> calls to shrink_slab(). Because of the poor multicore scalability of
>> atomic operations, this can lead to a significant drop in IPC
>> (instructions per cycle).
>>
>> We used to implement the lockless slab shrink with SRCU [2], but then
>> kernel test robot reported -88.8% regression in
>> stress-ng.ramfs.ops_per_sec test case [3], so we reverted it [4].
>>
>> This commit uses the refcount+RCU method [5] proposed by Dave Chinner
>> to re-implement the lockless global slab shrink. The memcg slab shrink is
>> handled in the subsequent patch.
>>
>> For now, all shrinker instances are converted to dynamically allocated and
>> will be freed by kfree_rcu(). So we can use rcu_read_{lock,unlock}() to
>> ensure that the shrinker instance is valid.
>>
>> And the shrinker instance will not be run again after unregistration. So
>> the structure that records the pointer of shrinker instance can be safely
>> freed without waiting for the RCU read-side critical section.
>>
>> In this way, while we implement the lockless slab shrink, we don't need to
>> be blocked in unregister_shrinker().
>>
>> The following are the test results:
>>
>> stress-ng --timeout 60 --times --verify --metrics-brief --ramfs 9 &
>>
>> 1) Before applying this patchset:
>>
>> setting to a 60 second run per stressor
>> dispatching hogs: 9 ramfs
>> stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
>>                            (secs)    (secs)    (secs)   (real time) (usr+sys time)
>> ramfs            735238     60.00     12.37    363.70     12253.05        1955.08
>> for a 60.01s run time:
>>     1440.27s available CPU time
>>       12.36s user time   (  0.86%)
>>      363.70s system time ( 25.25%)
>>      376.06s total time  ( 26.11%)
>> load average: 10.79 4.47 1.69
>> passed: 9: ramfs (9)
>> failed: 0
>> skipped: 0
>> successful run completed in 60.01s (1 min, 0.01 secs)
>>
>> 2) After applying this patchset:
>>
>> setting to a 60 second run per stressor
>> dispatching hogs: 9 ramfs
>> stressor       bogo ops real time  usr time  sys time   bogo ops/s     bogo ops/s
>>                            (secs)    (secs)    (secs)   (real time) (usr+sys time)
>> ramfs            746677     60.00     12.22    367.75     12443.70        1965.13
>> for a 60.01s run time:
>>     1440.26s available CPU time
>>       12.21s user time   (  0.85%)
>>      367.75s system time ( 25.53%)
>>      379.96s total time  ( 26.38%)
>> load average: 8.37 2.48 0.86
>> passed: 9: ramfs (9)
>> failed: 0
>> skipped: 0
>> successful run completed in 60.01s (1 min, 0.01 secs)
>>
>> We can see that the ops/s has hardly changed.
>>
>> [1]. https://lore.kernel.org/lkml/20191129214541.3110-1-ptikhomirov@virtuozzo.com/
>> [2]. https://lore.kernel.org/lkml/20230313112819.38938-1-zhengqi.arch@bytedance.com/
>> [3]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/
>> [4]. https://lore.kernel.org/all/20230609081518.3039120-1-qi.zheng@linux.dev/
>> [5]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   include/linux/shrinker.h | 19 +++++++---
>>   mm/shrinker.c            | 75 ++++++++++++++++++++++++++--------------
>>   mm/shrinker_debug.c      | 52 +++++++++++++++++++++-------
>>   3 files changed, 104 insertions(+), 42 deletions(-)
>>
>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
>> index 36977a70bebb..335da93cccee 100644
>> --- a/include/linux/shrinker.h
>> +++ b/include/linux/shrinker.h
>> @@ -4,6 +4,7 @@
>>   
>>   #include <linux/atomic.h>
>>   #include <linux/types.h>
>> +#include <linux/refcount.h>
>>   
>>   #define SHRINKER_UNIT_BITS	BITS_PER_LONG
>>   
>> @@ -86,6 +87,10 @@ struct shrinker {
>>   	long batch;	/* reclaim batch size, 0 = default */
>>   	int seeks;	/* seeks to recreate an obj */
>>   	unsigned flags;
>> +	bool registered;
>> +
>> +	refcount_t refcount;
>> +	struct rcu_head rcu;
>>   
>>   	void *private_data;
>>   
>> @@ -106,14 +111,13 @@ struct shrinker {
>>   #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
>>   
>>   /* Flags */
>> -#define SHRINKER_REGISTERED	(1 << 0)
>> -#define SHRINKER_NUMA_AWARE	(1 << 1)
>> -#define SHRINKER_MEMCG_AWARE	(1 << 2)
>> +#define SHRINKER_NUMA_AWARE	(1 << 0)
>> +#define SHRINKER_MEMCG_AWARE	(1 << 1)
>>   /*
>>    * It just makes sense when the shrinker is also MEMCG_AWARE for now,
>>    * non-MEMCG_AWARE shrinker should not have this flag set.
>>    */
>> -#define SHRINKER_NONSLAB	(1 << 3)
>> +#define SHRINKER_NONSLAB	(1 << 2)
>>   
>>   unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
>>   			  int priority);
>> @@ -122,6 +126,13 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
>>   void shrinker_register(struct shrinker *shrinker);
>>   void shrinker_unregister(struct shrinker *shrinker);
>>   
>> +static inline bool shrinker_try_get(struct shrinker *shrinker)
>> +{
>> +	return READ_ONCE(shrinker->registered) &&
>> +	       refcount_inc_not_zero(&shrinker->refcount);
>> +}
> 
> Why do we care about shrinker->registered here? If we don't set
> the refcount to 1 until we have fully initialised everything, then
> the shrinker code can key entirely off the reference count and
> none of the lookup code needs to care about whether the shrinker is
> registered or not.

The purpose of checking shrinker->registered here is to stop running
shrinker after calling shrinker_free(), which can prevent the following
situations from happening:

CPU 0                 CPU 1

shrinker_try_get()

                        shrinker_try_get()

shrinker_put()
shrinker_try_get()
                        shrinker_put()

This chance of this happening is small, but theoretically possible, so
I added this check.

> 
>> +void shrinker_put(struct shrinker *shrinker);
>> +
>>   #ifdef CONFIG_SHRINKER_DEBUG
>>   extern int shrinker_debugfs_add(struct shrinker *shrinker);
>>   extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
>> diff --git a/mm/shrinker.c b/mm/shrinker.c
>> index 8a1fe844f1a4..8e3334749552 100644
>> --- a/mm/shrinker.c
>> +++ b/mm/shrinker.c
>> @@ -2,10 +2,13 @@
>>   #include <linux/memcontrol.h>
>>   #include <linux/rwsem.h>
>>   #include <linux/shrinker.h>
>> +#include <linux/rculist.h>
>> +#include <linux/spinlock.h>
>>   #include <trace/events/vmscan.h>
>>   
>>   LIST_HEAD(shrinker_list);
>>   DECLARE_RWSEM(shrinker_rwsem);
>> +DEFINE_SPINLOCK(shrinker_lock);
>>   
>>   #ifdef CONFIG_MEMCG
>>   static int shrinker_nr_max;
>> @@ -450,6 +453,18 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>>   	return freed;
>>   }
>>   
>> +void shrinker_put(struct shrinker *shrinker)
>> +{
>> +	if (refcount_dec_and_test(&shrinker->refcount)) {
>> +		spin_lock(&shrinker_lock);
>> +		list_del_rcu(&shrinker->list);
>> +		spin_unlock(&shrinker_lock);
>> +
>> +		kfree(shrinker->nr_deferred);
>> +		kfree_rcu(shrinker, rcu);
>> +	}
>> +}
> 
> Urk, no.
> 
> We want the shrinker_free() code to block waiting for the shrinker
> reference count to go to zero, because the shrinkers can reference
> structures that are associated with the path that is freeing the
> shrinker.
> 
> i.e. we do not want to free the superblock of a filesystem whilst
> the shrinker is still running, but the way you've done this is that
> the shrinker can run whilst the structure that contains it has been
> torn down.

Oh, I missed this. I will change it back to use completion as soon as
possible.

> 
> This should use a completion, then it is always safe under
> rcu_read_lock().  This also gets rid of the shrinker_lock spin lock,
> which only exists because we can't take a blocking lock under
> rcu_read_lock(). i.e:
> 
> 
> void shrinker_put(struct shrinker *shrinker)
> {
> 	if (refcount_dec_and_test(&shrinker->refcount))
> 		complete(&shrinker->done);
> }
> 
> void shrinker_free()
> {
> 	.....
> 	refcount_dec(&shrinker->refcount);

I guess what you mean is shrinker_put(), because here may be the last
refcount.

> 	wait_for_completion(&shrinker->done);
> 	/*
> 	 * lookups on the shrinker will now all fail as refcount has
> 	 * fallen to zero. We can now remove it from the lists and
> 	 * free it.
> 	 */
> 	down_write(shrinker_rwsem);
> 	list_del_rcu(&shrinker->list);
> 	up_write(&shrinker_rwsem);
> 	call_rcu(shrinker->rcu_head, shrinker_free_rcu_cb);
> }
> 
> ....
> 
>> @@ -686,11 +711,14 @@ EXPORT_SYMBOL(shrinker_free_non_registered);
>>   
>>   void shrinker_register(struct shrinker *shrinker)
>>   {
>> -	down_write(&shrinker_rwsem);
>> -	list_add_tail(&shrinker->list, &shrinker_list);
>> -	shrinker->flags |= SHRINKER_REGISTERED;
>> +	refcount_set(&shrinker->refcount, 1);
>> +
>> +	spin_lock(&shrinker_lock);
>> +	list_add_tail_rcu(&shrinker->list, &shrinker_list);
>> +	spin_unlock(&shrinker_lock);
>> +
>>   	shrinker_debugfs_add(shrinker);
>> -	up_write(&shrinker_rwsem);
>> +	WRITE_ONCE(shrinker->registered, true);
>>   }
>>   EXPORT_SYMBOL(shrinker_register);
> 
> This just looks wrong - you are trying to use WRITE_ONCE() as a
> release barrier to indicate that the shrinker is now set up fully.
> That's not necessary - the refcount is an atomic and along with the
> rcu locks they should provides all the barriers we need. i.e.

The reason I used WRITE_ONCE() here is because the shrinker->registered
will be read and written concurrently (read in shrinker_try_get() and
written in shrinker_free()), which is why I added shrinker::registered
field instead of using SHRINKER_REGISTERED flag (this can reduce the
addition of WRITE_ONCE()/READ_ONCE()).

> 
> void shrinker_register(struct shrinker *shrinker)
> {
> 	down_write(&shrinker_rwsem);
> 	list_add_tail_rcu(&shrinker->list, &shrinker_list);
> 	shrinker->flags |= SHRINKER_REGISTERED;
> 	shrinker_debugfs_add(shrinker);
> 	up_write(&shrinker_rwsem);
> 
> 	/*
> 	 * now the shrinker is fully set up, take the first
> 	 * reference to it to indicate that lookup operations are
> 	 * now allowed to use it via shrinker_try_get().
> 	 */
> 	refcount_set(&shrinker->refcount, 1);
> }
> 
>> diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
>> index f1becfd45853..c5573066adbf 100644
>> --- a/mm/shrinker_debug.c
>> +++ b/mm/shrinker_debug.c
>> @@ -5,6 +5,7 @@
>>   #include <linux/seq_file.h>
>>   #include <linux/shrinker.h>
>>   #include <linux/memcontrol.h>
>> +#include <linux/rculist.h>
>>   
>>   /* defined in vmscan.c */
>>   extern struct rw_semaphore shrinker_rwsem;
>> @@ -161,17 +162,21 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>>   {
>>   	struct dentry *entry;
>>   	char buf[128];
>> -	int id;
>> -
>> -	lockdep_assert_held(&shrinker_rwsem);
>> +	int id, ret = 0;
>>   
>>   	/* debugfs isn't initialized yet, add debugfs entries later. */
>>   	if (!shrinker_debugfs_root)
>>   		return 0;
>>   
>> +	down_write(&shrinker_rwsem);
>> +	if (shrinker->debugfs_entry)
>> +		goto fail;
>> +
>>   	id = ida_alloc(&shrinker_debugfs_ida, GFP_KERNEL);
>> -	if (id < 0)
>> -		return id;
>> +	if (id < 0) {
>> +		ret = id;
>> +		goto fail;
>> +	}
>>   	shrinker->debugfs_id = id;
>>   
>>   	snprintf(buf, sizeof(buf), "%s-%d", shrinker->name, id);
>> @@ -180,7 +185,8 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>>   	entry = debugfs_create_dir(buf, shrinker_debugfs_root);
>>   	if (IS_ERR(entry)) {
>>   		ida_free(&shrinker_debugfs_ida, id);
>> -		return PTR_ERR(entry);
>> +		ret = PTR_ERR(entry);
>> +		goto fail;
>>   	}
>>   	shrinker->debugfs_entry = entry;
>>   
>> @@ -188,7 +194,10 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>>   			    &shrinker_debugfs_count_fops);
>>   	debugfs_create_file("scan", 0220, entry, shrinker,
>>   			    &shrinker_debugfs_scan_fops);
>> -	return 0;
>> +
>> +fail:
>> +	up_write(&shrinker_rwsem);
>> +	return ret;
>>   }
>>   
>>   int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
>> @@ -243,6 +252,11 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
>>   	shrinker->name = NULL;
>>   
>>   	*debugfs_id = entry ? shrinker->debugfs_id : -1;
>> +	/*
>> +	 * Ensure that shrinker->registered has been set to false before
>> +	 * shrinker->debugfs_entry is set to NULL.
>> +	 */
>> +	smp_wmb();
>>   	shrinker->debugfs_entry = NULL;
>>   
>>   	return entry;
>> @@ -266,14 +280,26 @@ static int __init shrinker_debugfs_init(void)
>>   	shrinker_debugfs_root = dentry;
>>   
>>   	/* Create debugfs entries for shrinkers registered at boot */
>> -	down_write(&shrinker_rwsem);
>> -	list_for_each_entry(shrinker, &shrinker_list, list)
>> +	rcu_read_lock();
>> +	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
>> +		if (!shrinker_try_get(shrinker))
>> +			continue;
>> +		rcu_read_unlock();
>> +
>>   		if (!shrinker->debugfs_entry) {
>> -			ret = shrinker_debugfs_add(shrinker);
>> -			if (ret)
>> -				break;
>> +			/* Paired with smp_wmb() in shrinker_debugfs_detach() */
>> +			smp_rmb();
>> +			if (READ_ONCE(shrinker->registered))
>> +				ret = shrinker_debugfs_add(shrinker);
>>   		}
>> -	up_write(&shrinker_rwsem);
>> +
>> +		rcu_read_lock();
>> +		shrinker_put(shrinker);
>> +
>> +		if (ret)
>> +			break;
>> +	}
>> +	rcu_read_unlock();
>>   
>>   	return ret;
>>   }
> 
> And all this churn and complexity can go away because the
> shrinker_rwsem is still used to protect shrinker_register()
> entirely....

My consideration is that during this process, there may be a
driver probe failure and then shrinker_free() is called (the
shrinker_debugfs_init() is called in late_initcall stage). In
this case, we need to use RCU+refcount to ensure that the shrinker
is not freed.

And after switching back to using completion, the smp_rmb()/smp_wmb()
is no longer needed.

Thanks,
Qi

> 
> -Dave.

Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Qi Zheng]

Hi Dave,

On 2023/7/26 15:26, Dave Chinner wrote:
> On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote:
>> Currently, the shrinker instances can be divided into the following three
>> types:
>>
>> a) global shrinker instance statically defined in the kernel, such as
>>     workingset_shadow_shrinker.
>>
>> b) global shrinker instance statically defined in the kernel modules, such
>>     as mmu_shrinker in x86.
>>
>> c) shrinker instance embedded in other structures.
>>
>> For case a, the memory of shrinker instance is never freed. For case b,
>> the memory of shrinker instance will be freed after synchronize_rcu() when
>> the module is unloaded. For case c, the memory of shrinker instance will
>> be freed along with the structure it is embedded in.
>>
>> In preparation for implementing lockless slab shrink, we need to
>> dynamically allocate those shrinker instances in case c, then the memory
>> can be dynamically freed alone by calling kfree_rcu().
>>
>> So this commit adds the following new APIs for dynamically allocating
>> shrinker, and add a private_data field to struct shrinker to record and
>> get the original embedded structure.
>>
>> 1. shrinker_alloc()
>>
>> Used to allocate shrinker instance itself and related memory, it will
>> return a pointer to the shrinker instance on success and NULL on failure.
>>
>> 2. shrinker_free_non_registered()
>>
>> Used to destroy the non-registered shrinker instance.
> 
> This is a bit nasty
> 
>>
>> 3. shrinker_register()
>>
>> Used to register the shrinker instance, which is same as the current
>> register_shrinker_prepared().
>>
>> 4. shrinker_unregister()
> 
> rename this "shrinker_free()" and key the two different freeing
> cases on the SHRINKER_REGISTERED bit rather than mostly duplicating
> the two.

OK, will do in the next version.

> 
> void shrinker_free(struct shrinker *shrinker)
> {
> 	struct dentry *debugfs_entry = NULL;
> 	int debugfs_id;
> 
> 	if (!shrinker)
> 		return;
> 
> 	down_write(&shrinker_rwsem);
> 	if (shrinker->flags & SHRINKER_REGISTERED) {
> 		list_del(&shrinker->list);
> 		debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
> 	} else if (IS_ENABLED(CONFIG_SHRINKER_DEBUG)) {
> 		kfree_const(shrinker->name);
> 	}
> 
> 	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> 		unregister_memcg_shrinker(shrinker);
> 	up_write(&shrinker_rwsem);
> 
> 	if (debugfs_entry)
> 		shrinker_debugfs_remove(debugfs_entry, debugfs_id);
> 
> 	kfree(shrinker->nr_deferred);
> 	kfree(shrinker);
> }
> EXPORT_SYMBOL_GPL(shrinker_free);

Ah, I will change all new APIs to use EXPORT_SYMBOL_GPL().

Thanks,
Qi

> 

Re: [PATCH v2 11/47] gfs2: dynamically allocate the gfs2-qd shrinker

[Qi Zheng]

On 2023/7/26 14:49, Muchun Song wrote:
> 
> 
> On 2023/7/24 17:43, Qi Zheng wrote:
>> Use new APIs to dynamically allocate the gfs2-qd shrinker.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   fs/gfs2/main.c  |  6 +++---
>>   fs/gfs2/quota.c | 26 ++++++++++++++++++++------
>>   fs/gfs2/quota.h |  3 ++-
>>   3 files changed, 25 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/gfs2/main.c b/fs/gfs2/main.c
>> index afcb32854f14..e47b1cc79f59 100644
>> --- a/fs/gfs2/main.c
>> +++ b/fs/gfs2/main.c
>> @@ -147,7 +147,7 @@ static int __init init_gfs2_fs(void)
>>       if (!gfs2_trans_cachep)
>>           goto fail_cachep8;
>> -    error = register_shrinker(&gfs2_qd_shrinker, "gfs2-qd");
>> +    error = gfs2_qd_shrinker_init();
>>       if (error)
>>           goto fail_shrinker;
>> @@ -196,7 +196,7 @@ static int __init init_gfs2_fs(void)
>>   fail_wq2:
>>       destroy_workqueue(gfs_recovery_wq);
>>   fail_wq1:
>> -    unregister_shrinker(&gfs2_qd_shrinker);
>> +    gfs2_qd_shrinker_exit();
>>   fail_shrinker:
>>       kmem_cache_destroy(gfs2_trans_cachep);
>>   fail_cachep8:
>> @@ -229,7 +229,7 @@ static int __init init_gfs2_fs(void)
>>   static void __exit exit_gfs2_fs(void)
>>   {
>> -    unregister_shrinker(&gfs2_qd_shrinker);
>> +    gfs2_qd_shrinker_exit();
>>       gfs2_glock_exit();
>>       gfs2_unregister_debugfs();
>>       unregister_filesystem(&gfs2_fs_type);
>> diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
>> index 704192b73605..bc9883cea847 100644
>> --- a/fs/gfs2/quota.c
>> +++ b/fs/gfs2/quota.c
>> @@ -186,13 +186,27 @@ static unsigned long gfs2_qd_shrink_count(struct 
>> shrinker *shrink,
>>       return vfs_pressure_ratio(list_lru_shrink_count(&gfs2_qd_lru, sc));
>>   }
>> -struct shrinker gfs2_qd_shrinker = {
>> -    .count_objects = gfs2_qd_shrink_count,
>> -    .scan_objects = gfs2_qd_shrink_scan,
>> -    .seeks = DEFAULT_SEEKS,
>> -    .flags = SHRINKER_NUMA_AWARE,
>> -};
>> +static struct shrinker *gfs2_qd_shrinker;
>> +
>> +int gfs2_qd_shrinker_init(void)
> 
> It's better to declare this as __init.

OK, Will do.

> 
>> +{
>> +    gfs2_qd_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE, "gfs2-qd");
>> +    if (!gfs2_qd_shrinker)
>> +        return -ENOMEM;
>> +
>> +    gfs2_qd_shrinker->count_objects = gfs2_qd_shrink_count;
>> +    gfs2_qd_shrinker->scan_objects = gfs2_qd_shrink_scan;
>> +    gfs2_qd_shrinker->seeks = DEFAULT_SEEKS;
>> +
>> +    shrinker_register(gfs2_qd_shrinker);
>> +    return 0;
>> +}
>> +
>> +void gfs2_qd_shrinker_exit(void)
>> +{
>> +    shrinker_unregister(gfs2_qd_shrinker);
>> +}
>>   static u64 qd2index(struct gfs2_quota_data *qd)
>>   {
>> diff --git a/fs/gfs2/quota.h b/fs/gfs2/quota.h
>> index 21ada332d555..f9cb863373f7 100644
>> --- a/fs/gfs2/quota.h
>> +++ b/fs/gfs2/quota.h
>> @@ -59,7 +59,8 @@ static inline int gfs2_quota_lock_check(struct 
>> gfs2_inode *ip,
>>   }
>>   extern const struct quotactl_ops gfs2_quotactl_ops;
>> -extern struct shrinker gfs2_qd_shrinker;
>> +int gfs2_qd_shrinker_init(void);
>> +void gfs2_qd_shrinker_exit(void);
>>   extern struct list_lru gfs2_qd_lru;
>>   extern void __init gfs2_quota_hash_init(void);
> 

Re: [PATCH v2 17/47] rcu: dynamically allocate the rcu-lazy shrinker

[Qi Zheng]

On 2023/7/26 15:04, Muchun Song wrote:
> 
> 
>> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>>
>> Use new APIs to dynamically allocate the rcu-lazy shrinker.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>> kernel/rcu/tree_nocb.h | 19 +++++++++++--------
>> 1 file changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
>> index 43229d2b0c44..919f17561733 100644
>> --- a/kernel/rcu/tree_nocb.h
>> +++ b/kernel/rcu/tree_nocb.h
>> @@ -1397,12 +1397,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
>> return count ? count : SHRINK_STOP;
>> }
>>
>> -static struct shrinker lazy_rcu_shrinker = {
>> -	.count_objects = lazy_rcu_shrink_count,
>> -	.scan_objects = lazy_rcu_shrink_scan,
>> -	.batch = 0,
>> -	.seeks = DEFAULT_SEEKS,
>> -};
>> +static struct shrinker *lazy_rcu_shrinker;
> 
> Seems there is no users of this variable, maybe we could drop
> this.

Yeah, will change it to a local variable. And the patch #15 is
the same.

> 

Re: [PATCH v2 19/47] mm: thp: dynamically allocate the thp-related shrinkers

[Qi Zheng]

On 2023/7/26 15:10, Muchun Song wrote:
> 
> 
> On 2023/7/24 17:43, Qi Zheng wrote:
>> Use new APIs to dynamically allocate the thp-zero and thp-deferred_split
>> shrinkers.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   mm/huge_memory.c | 69 +++++++++++++++++++++++++++++++-----------------
>>   1 file changed, 45 insertions(+), 24 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 8c94b34024a2..4db5a1834d81 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -65,7 +65,11 @@ unsigned long transparent_hugepage_flags 
>> __read_mostly =
>>       (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
>>       (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
>> -static struct shrinker deferred_split_shrinker;
>> +static struct shrinker *deferred_split_shrinker;
>> +static unsigned long deferred_split_count(struct shrinker *shrink,
>> +                      struct shrink_control *sc);
>> +static unsigned long deferred_split_scan(struct shrinker *shrink,
>> +                     struct shrink_control *sc);
>>   static atomic_t huge_zero_refcount;
>>   struct page *huge_zero_page __read_mostly;
>> @@ -229,11 +233,7 @@ static unsigned long 
>> shrink_huge_zero_page_scan(struct shrinker *shrink,
>>       return 0;
>>   }
>> -static struct shrinker huge_zero_page_shrinker = {
>> -    .count_objects = shrink_huge_zero_page_count,
>> -    .scan_objects = shrink_huge_zero_page_scan,
>> -    .seeks = DEFAULT_SEEKS,
>> -};
>> +static struct shrinker *huge_zero_page_shrinker;
> 
> Same as patch #17.

OK, will do.

> 
>>   #ifdef CONFIG_SYSFS
>>   static ssize_t enabled_show(struct kobject *kobj,
>> @@ -454,6 +454,40 @@ static inline void hugepage_exit_sysfs(struct 
>> kobject *hugepage_kobj)
>>   }
>>   #endif /* CONFIG_SYSFS */
>> +static int thp_shrinker_init(void)
> 
> Better to declare it as __init.

Will do.

> 
>> +{
>> +    huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
>> +    if (!huge_zero_page_shrinker)
>> +        return -ENOMEM;
>> +
>> +    deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
>> +                         SHRINKER_MEMCG_AWARE |
>> +                         SHRINKER_NONSLAB,
>> +                         "thp-deferred_split");
>> +    if (!deferred_split_shrinker) {
>> +        shrinker_free_non_registered(huge_zero_page_shrinker);
>> +        return -ENOMEM;
>> +    }
>> +
>> +    huge_zero_page_shrinker->count_objects = 
>> shrink_huge_zero_page_count;
>> +    huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
>> +    huge_zero_page_shrinker->seeks = DEFAULT_SEEKS;
>> +    shrinker_register(huge_zero_page_shrinker);
>> +
>> +    deferred_split_shrinker->count_objects = deferred_split_count;
>> +    deferred_split_shrinker->scan_objects = deferred_split_scan;
>> +    deferred_split_shrinker->seeks = DEFAULT_SEEKS;
>> +    shrinker_register(deferred_split_shrinker);
>> +
>> +    return 0;
>> +}
>> +
>> +static void thp_shrinker_exit(void)
> 
> Same as here.

Will do.

> 
>> +{
>> +    shrinker_unregister(huge_zero_page_shrinker);
>> +    shrinker_unregister(deferred_split_shrinker);
>> +}
>> +
>>   static int __init hugepage_init(void)
>>   {
>>       int err;
>> @@ -482,12 +516,9 @@ static int __init hugepage_init(void)
>>       if (err)
>>           goto err_slab;
>> -    err = register_shrinker(&huge_zero_page_shrinker, "thp-zero");
>> -    if (err)
>> -        goto err_hzp_shrinker;
>> -    err = register_shrinker(&deferred_split_shrinker, 
>> "thp-deferred_split");
>> +    err = thp_shrinker_init();
>>       if (err)
>> -        goto err_split_shrinker;
>> +        goto err_shrinker;
>>       /*
>>        * By default disable transparent hugepages on smaller systems,
>> @@ -505,10 +536,8 @@ static int __init hugepage_init(void)
>>       return 0;
>>   err_khugepaged:
>> -    unregister_shrinker(&deferred_split_shrinker);
>> -err_split_shrinker:
>> -    unregister_shrinker(&huge_zero_page_shrinker);
>> -err_hzp_shrinker:
>> +    thp_shrinker_exit();
>> +err_shrinker:
>>       khugepaged_destroy();
>>   err_slab:
>>       hugepage_exit_sysfs(hugepage_kobj);
>> @@ -2851,7 +2880,7 @@ void deferred_split_folio(struct folio *folio)
>>   #ifdef CONFIG_MEMCG
>>           if (memcg)
>>               set_shrinker_bit(memcg, folio_nid(folio),
>> -                     deferred_split_shrinker.id);
>> +                     deferred_split_shrinker->id);
>>   #endif
>>       }
>>       spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>> @@ -2925,14 +2954,6 @@ static unsigned long deferred_split_scan(struct 
>> shrinker *shrink,
>>       return split;
>>   }
>> -static struct shrinker deferred_split_shrinker = {
>> -    .count_objects = deferred_split_count,
>> -    .scan_objects = deferred_split_scan,
>> -    .seeks = DEFAULT_SEEKS,
>> -    .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE |
>> -         SHRINKER_NONSLAB,
>> -};
>> -
>>   #ifdef CONFIG_DEBUG_FS
>>   static void split_huge_pages_all(void)
>>   {
> 

Re: [PATCH v2 21/47] mm: workingset: dynamically allocate the mm-shadow shrinker

[Qi Zheng]

On 2023/7/26 15:13, Muchun Song wrote:
> 
> 
>> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>>
>> Use new APIs to dynamically allocate the mm-shadow shrinker.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>> mm/workingset.c | 26 ++++++++++++++------------
>> 1 file changed, 14 insertions(+), 12 deletions(-)
>>
>> diff --git a/mm/workingset.c b/mm/workingset.c
>> index 4686ae363000..4bc85f739b13 100644
>> --- a/mm/workingset.c
>> +++ b/mm/workingset.c
>> @@ -762,12 +762,7 @@ static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
>> NULL);
>> }
>>
>> -static struct shrinker workingset_shadow_shrinker = {
>> -	.count_objects = count_shadow_nodes,
>> -	.scan_objects = scan_shadow_nodes,
>> -	.seeks = 0, /* ->count reports only fully expendable nodes */
>> -	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
>> -};
>> +static struct shrinker *workingset_shadow_shrinker;
> 
> 
> Same as patch #17.

OK, will do.

Re: [PATCH v2 43/47] mm: shrinker: add a secondary array for shrinker_info::{map, nr_deferred}

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> Currently, we maintain two linear arrays per node per memcg, which are
> shrinker_info::map and shrinker_info::nr_deferred. And we need to resize
> them when the shrinker_nr_max is exceeded, that is, allocate a new array,
> and then copy the old array to the new array, and finally free the old
> array by RCU.
> 
> For shrinker_info::map, we do set_bit() under the RCU lock, so we may set
> the value into the old map which is about to be freed. This may cause the
> value set to be lost. The current solution is not to copy the old map when
> resizing, but to set all the corresponding bits in the new map to 1. This
> solves the data loss problem, but bring the overhead of more pointless
> loops while doing memcg slab shrink.
> 
> For shrinker_info::nr_deferred, we will only modify it under the read lock
> of shrinker_rwsem, so it will not run concurrently with the resizing. But
> after we make memcg slab shrink lockless, there will be the same data loss
> problem as shrinker_info::map, and we can't work around it like the map.
> 
> For such resizable arrays, the most straightforward idea is to change it
> to xarray, like we did for list_lru [1]. We need to do xa_store() in the
> list_lru_add()-->set_shrinker_bit(), but this will cause memory
> allocation, and the list_lru_add() doesn't accept failure. A possible
> solution is to pre-allocate, but the location of pre-allocation is not
> well determined.
> 
> Therefore, this commit chooses to introduce a secondary array for
> shrinker_info::{map, nr_deferred}, so that we only need to copy this
> secondary array every time the size is resized. Then even if we get the
> old secondary array under the RCU lock, the found map and nr_deferred are
> also true, so no data is lost.
> 
> [1]. https://lore.kernel.org/all/20220228122126.37293-13-songmuchun@bytedance.com/
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Re: [PATCH v2 23/47] drm/msm: dynamically allocate the drm-msm_gem shrinker

[Qi Zheng]

On 2023/7/26 15:24, Muchun Song wrote:
> 
> 
> On 2023/7/24 17:43, Qi Zheng wrote:
>> In preparation for implementing lockless slab shrink, use new APIs to
>> dynamically allocate the drm-msm_gem shrinker, so that it can be freed
>> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
>> read-side critical section when releasing the struct msm_drm_private.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> 
> A nit bellow.
> 
>> ---
>>   drivers/gpu/drm/msm/msm_drv.c          |  4 ++-
>>   drivers/gpu/drm/msm/msm_drv.h          |  4 +--
>>   drivers/gpu/drm/msm/msm_gem_shrinker.c | 36 ++++++++++++++++----------
>>   3 files changed, 28 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/msm_drv.c 
>> b/drivers/gpu/drm/msm/msm_drv.c
>> index 891eff8433a9..7f6933be703f 100644
>> --- a/drivers/gpu/drm/msm/msm_drv.c
>> +++ b/drivers/gpu/drm/msm/msm_drv.c
>> @@ -461,7 +461,9 @@ static int msm_drm_init(struct device *dev, const 
>> struct drm_driver *drv)
>>       if (ret)
>>           goto err_msm_uninit;
>> -    msm_gem_shrinker_init(ddev);
>> +    ret = msm_gem_shrinker_init(ddev);
>> +    if (ret)
>> +        goto err_msm_uninit;
>>       if (priv->kms_init) {
>>           ret = priv->kms_init(ddev);
>> diff --git a/drivers/gpu/drm/msm/msm_drv.h 
>> b/drivers/gpu/drm/msm/msm_drv.h
>> index e13a8cbd61c9..84523d4a1e58 100644
>> --- a/drivers/gpu/drm/msm/msm_drv.h
>> +++ b/drivers/gpu/drm/msm/msm_drv.h
>> @@ -217,7 +217,7 @@ struct msm_drm_private {
>>       } vram;
>>       struct notifier_block vmap_notifier;
>> -    struct shrinker shrinker;
>> +    struct shrinker *shrinker;
>>       struct drm_atomic_state *pm_state;
>> @@ -279,7 +279,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, 
>> void *data,
>>   unsigned long msm_gem_shrinker_shrink(struct drm_device *dev, 
>> unsigned long nr_to_scan);
>>   #endif
>> -void msm_gem_shrinker_init(struct drm_device *dev);
>> +int msm_gem_shrinker_init(struct drm_device *dev);
>>   void msm_gem_shrinker_cleanup(struct drm_device *dev);
>>   int msm_gem_prime_mmap(struct drm_gem_object *obj, struct 
>> vm_area_struct *vma);
>> diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c 
>> b/drivers/gpu/drm/msm/msm_gem_shrinker.c
>> index f38296ad8743..7daab1298c11 100644
>> --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
>> +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
>> @@ -34,8 +34,7 @@ static bool can_block(struct shrink_control *sc)
>>   static unsigned long
>>   msm_gem_shrinker_count(struct shrinker *shrinker, struct 
>> shrink_control *sc)
>>   {
>> -    struct msm_drm_private *priv =
>> -        container_of(shrinker, struct msm_drm_private, shrinker);
>> +    struct msm_drm_private *priv = shrinker->private_data;
>>       unsigned count = priv->lru.dontneed.count;
>>       if (can_swap())
>> @@ -100,8 +99,7 @@ active_evict(struct drm_gem_object *obj)
>>   static unsigned long
>>   msm_gem_shrinker_scan(struct shrinker *shrinker, struct 
>> shrink_control *sc)
>>   {
>> -    struct msm_drm_private *priv =
>> -        container_of(shrinker, struct msm_drm_private, shrinker);
>> +    struct msm_drm_private *priv = shrinker->private_data;
>>       struct {
>>           struct drm_gem_lru *lru;
>>           bool (*shrink)(struct drm_gem_object *obj);
>> @@ -148,10 +146,11 @@ msm_gem_shrinker_shrink(struct drm_device *dev, 
>> unsigned long nr_to_scan)
>>       struct shrink_control sc = {
>>           .nr_to_scan = nr_to_scan,
>>       };
>> -    int ret;
>> +    unsigned long ret = SHRINK_STOP;
>>       fs_reclaim_acquire(GFP_KERNEL);
>> -    ret = msm_gem_shrinker_scan(&priv->shrinker, &sc);
>> +    if (priv->shrinker)
>> +        ret = msm_gem_shrinker_scan(priv->shrinker, &sc);
>>       fs_reclaim_release(GFP_KERNEL);
>>       return ret;
>> @@ -210,16 +209,27 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, 
>> unsigned long event, void *ptr)
>>    *
>>    * This function registers and sets up the msm shrinker.
>>    */
>> -void msm_gem_shrinker_init(struct drm_device *dev)
>> +int msm_gem_shrinker_init(struct drm_device *dev)
>>   {
>>       struct msm_drm_private *priv = dev->dev_private;
>> -    priv->shrinker.count_objects = msm_gem_shrinker_count;
>> -    priv->shrinker.scan_objects = msm_gem_shrinker_scan;
>> -    priv->shrinker.seeks = DEFAULT_SEEKS;
>> -    WARN_ON(register_shrinker(&priv->shrinker, "drm-msm_gem"));
>> +
>> +    priv->shrinker = shrinker_alloc(0, "drm-msm_gem");
>> +    if (!priv->shrinker) {
> 
> Just "if (WARN_ON(!priv->shrinker))"

As suggested by Steven Pric in patch #24, this warning is
unnecessary, so I will remove it in the next version.

> 
>> +        WARN_ON(1);
>> +        return -ENOMEM;
>> +    }
>> +
>> +    priv->shrinker->count_objects = msm_gem_shrinker_count;
>> +    priv->shrinker->scan_objects = msm_gem_shrinker_scan;
>> +    priv->shrinker->seeks = DEFAULT_SEEKS;
>> +    priv->shrinker->private_data = priv;
>> +
>> +    shrinker_register(priv->shrinker);
>>       priv->vmap_notifier.notifier_call = msm_gem_shrinker_vmap;
>>       WARN_ON(register_vmap_purge_notifier(&priv->vmap_notifier));
>> +
>> +    return 0;
>>   }
>>   /**
>> @@ -232,8 +242,8 @@ void msm_gem_shrinker_cleanup(struct drm_device *dev)
>>   {
>>       struct msm_drm_private *priv = dev->dev_private;
>> -    if (priv->shrinker.nr_deferred) {
>> +    if (priv->shrinker) {
>>           WARN_ON(unregister_vmap_purge_notifier(&priv->vmap_notifier));
>> -        unregister_shrinker(&priv->shrinker);
>> +        shrinker_unregister(priv->shrinker);
>>       }
>>   }
> 

Re: [PATCH v2 28/47] bcache: dynamically allocate the md-bcache shrinker

[Qi Zheng]

On 2023/7/26 15:32, Muchun Song wrote:
> 
> 
> On 2023/7/24 17:43, Qi Zheng wrote:
>> In preparation for implementing lockless slab shrink, use new APIs to
>> dynamically allocate the md-bcache shrinker, so that it can be freed
>> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
>> read-side critical section when releasing the struct cache_set.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   drivers/md/bcache/bcache.h |  2 +-
>>   drivers/md/bcache/btree.c  | 27 ++++++++++++++++-----------
>>   drivers/md/bcache/sysfs.c  |  3 ++-
>>   3 files changed, 19 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
>> index 5a79bb3c272f..c622bc50f81b 100644
>> --- a/drivers/md/bcache/bcache.h
>> +++ b/drivers/md/bcache/bcache.h
>> @@ -541,7 +541,7 @@ struct cache_set {
>>       struct bio_set        bio_split;
>>       /* For the btree cache */
>> -    struct shrinker        shrink;
>> +    struct shrinker        *shrink;
>>       /* For the btree cache and anything allocation related */
>>       struct mutex        bucket_lock;
>> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
>> index fd121a61f17c..c176c7fc77d9 100644
>> --- a/drivers/md/bcache/btree.c
>> +++ b/drivers/md/bcache/btree.c
>> @@ -667,7 +667,7 @@ static int mca_reap(struct btree *b, unsigned int 
>> min_order, bool flush)
>>   static unsigned long bch_mca_scan(struct shrinker *shrink,
>>                     struct shrink_control *sc)
>>   {
>> -    struct cache_set *c = container_of(shrink, struct cache_set, 
>> shrink);
>> +    struct cache_set *c = shrink->private_data;
>>       struct btree *b, *t;
>>       unsigned long i, nr = sc->nr_to_scan;
>>       unsigned long freed = 0;
>> @@ -734,7 +734,7 @@ static unsigned long bch_mca_scan(struct shrinker 
>> *shrink,
>>   static unsigned long bch_mca_count(struct shrinker *shrink,
>>                      struct shrink_control *sc)
>>   {
>> -    struct cache_set *c = container_of(shrink, struct cache_set, 
>> shrink);
>> +    struct cache_set *c = shrink->private_data;
>>       if (c->shrinker_disabled)
>>           return 0;
>> @@ -752,8 +752,8 @@ void bch_btree_cache_free(struct cache_set *c)
>>       closure_init_stack(&cl);
>> -    if (c->shrink.list.next)
>> -        unregister_shrinker(&c->shrink);
>> +    if (c->shrink)
>> +        shrinker_unregister(c->shrink);
>>       mutex_lock(&c->bucket_lock);
>> @@ -828,14 +828,19 @@ int bch_btree_cache_alloc(struct cache_set *c)
>>           c->verify_data = NULL;
>>   #endif
>> -    c->shrink.count_objects = bch_mca_count;
>> -    c->shrink.scan_objects = bch_mca_scan;
>> -    c->shrink.seeks = 4;
>> -    c->shrink.batch = c->btree_pages * 2;
>> +    c->shrink = shrinker_alloc(0, "md-bcache:%pU", c->set_uuid);
>> +    if (!c->shrink) {
>> +        pr_warn("bcache: %s: could not allocate shrinker\n", __func__);
>> +        return -ENOMEM;
> 
> Seems you have cheanged the semantic of this. In the past,
> it is better to have a shrinker, but now it becomes a mandatory.
> Right? I don't know if it is acceptable. From my point of view,
> just do the cleanup, don't change any behaviour.

Oh, should return 0 here, will do.

> 
>> +    }
>> +
>> +    c->shrink->count_objects = bch_mca_count;
>> +    c->shrink->scan_objects = bch_mca_scan;
>> +    c->shrink->seeks = 4;
>> +    c->shrink->batch = c->btree_pages * 2;
>> +    c->shrink->private_data = c;
>> -    if (register_shrinker(&c->shrink, "md-bcache:%pU", c->set_uuid))
>> -        pr_warn("bcache: %s: could not register shrinker\n",
>> -                __func__);
>> +    shrinker_register(c->shrink);
>>       return 0;
>>   }
>> diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
>> index 0e2c1880f60b..45d8af755de6 100644
>> --- a/drivers/md/bcache/sysfs.c
>> +++ b/drivers/md/bcache/sysfs.c
>> @@ -866,7 +866,8 @@ STORE(__bch_cache_set)
>>           sc.gfp_mask = GFP_KERNEL;
>>           sc.nr_to_scan = strtoul_or_return(buf);
>> -        c->shrink.scan_objects(&c->shrink, &sc);
>> +        if (c->shrink)
>> +            c->shrink->scan_objects(c->shrink, &sc);
>>       }
>>       sysfs_strtoul_clamp(congested_read_threshold_us,
> 

Re: [PATCH v2 44/47] mm: shrinker: make global slab shrink lockless

[Dave Chinner]

On Wed, Jul 26, 2023 at 05:14:09PM +0800, Qi Zheng wrote:
> On 2023/7/26 16:08, Dave Chinner wrote:
> > On Mon, Jul 24, 2023 at 05:43:51PM +0800, Qi Zheng wrote:
> > > @@ -122,6 +126,13 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
> > >   void shrinker_register(struct shrinker *shrinker);
> > >   void shrinker_unregister(struct shrinker *shrinker);
> > > +static inline bool shrinker_try_get(struct shrinker *shrinker)
> > > +{
> > > +	return READ_ONCE(shrinker->registered) &&
> > > +	       refcount_inc_not_zero(&shrinker->refcount);
> > > +}
> > 
> > Why do we care about shrinker->registered here? If we don't set
> > the refcount to 1 until we have fully initialised everything, then
> > the shrinker code can key entirely off the reference count and
> > none of the lookup code needs to care about whether the shrinker is
> > registered or not.
> 
> The purpose of checking shrinker->registered here is to stop running
> shrinker after calling shrinker_free(), which can prevent the following
> situations from happening:
> 
> CPU 0                 CPU 1
> 
> shrinker_try_get()
> 
>                        shrinker_try_get()
> 
> shrinker_put()
> shrinker_try_get()
>                        shrinker_put()

I don't see any race here? What is wrong with having multiple active
users at once?

> > 
> > This should use a completion, then it is always safe under
> > rcu_read_lock().  This also gets rid of the shrinker_lock spin lock,
> > which only exists because we can't take a blocking lock under
> > rcu_read_lock(). i.e:
> > 
> > 
> > void shrinker_put(struct shrinker *shrinker)
> > {
> > 	if (refcount_dec_and_test(&shrinker->refcount))
> > 		complete(&shrinker->done);
> > }
> > 
> > void shrinker_free()
> > {
> > 	.....
> > 	refcount_dec(&shrinker->refcount);
> 
> I guess what you mean is shrinker_put(), because here may be the last
> refcount.

Yes, I did.

> > 	wait_for_completion(&shrinker->done);
> > 	/*
> > 	 * lookups on the shrinker will now all fail as refcount has
> > 	 * fallen to zero. We can now remove it from the lists and
> > 	 * free it.
> > 	 */
> > 	down_write(shrinker_rwsem);
> > 	list_del_rcu(&shrinker->list);
> > 	up_write(&shrinker_rwsem);
> > 	call_rcu(shrinker->rcu_head, shrinker_free_rcu_cb);
> > }
> > 
> > ....
> > 
> > > @@ -686,11 +711,14 @@ EXPORT_SYMBOL(shrinker_free_non_registered);
> > >   void shrinker_register(struct shrinker *shrinker)
> > >   {
> > > -	down_write(&shrinker_rwsem);
> > > -	list_add_tail(&shrinker->list, &shrinker_list);
> > > -	shrinker->flags |= SHRINKER_REGISTERED;
> > > +	refcount_set(&shrinker->refcount, 1);
> > > +
> > > +	spin_lock(&shrinker_lock);
> > > +	list_add_tail_rcu(&shrinker->list, &shrinker_list);
> > > +	spin_unlock(&shrinker_lock);
> > > +
> > >   	shrinker_debugfs_add(shrinker);
> > > -	up_write(&shrinker_rwsem);
> > > +	WRITE_ONCE(shrinker->registered, true);
> > >   }
> > >   EXPORT_SYMBOL(shrinker_register);
> > 
> > This just looks wrong - you are trying to use WRITE_ONCE() as a
> > release barrier to indicate that the shrinker is now set up fully.
> > That's not necessary - the refcount is an atomic and along with the
> > rcu locks they should provides all the barriers we need. i.e.
> 
> The reason I used WRITE_ONCE() here is because the shrinker->registered
> will be read and written concurrently (read in shrinker_try_get() and
> written in shrinker_free()), which is why I added shrinker::registered
> field instead of using SHRINKER_REGISTERED flag (this can reduce the
> addition of WRITE_ONCE()/READ_ONCE()).

Using WRITE_ONCE/READ_ONCE doesn't provide memory barriers needed to
use the field like this. You need release/acquire memory ordering
here. i.e. smp_store_release()/smp_load_acquire().

As it is, the refcount_inc_not_zero() provides a control dependency,
as documented in include/linux/refcount.h, refcount_dec_and_test()
provides release memory ordering. The only thing I think we may need
is a write barrier before refcount_set(), such that if
refcount_inc_not_zero() sees a non-zero value, it is guaranteed to
see an initialised structure...

i.e. refcounts provide all the existence and initialisation
guarantees. Hence I don't see the need to use shrinker->registered
like this and it can remain a bit flag protected by the
shrinker_rwsem().


> > void shrinker_register(struct shrinker *shrinker)
> > {
> > 	down_write(&shrinker_rwsem);
> > 	list_add_tail_rcu(&shrinker->list, &shrinker_list);
> > 	shrinker->flags |= SHRINKER_REGISTERED;
> > 	shrinker_debugfs_add(shrinker);
> > 	up_write(&shrinker_rwsem);
> > 
> > 	/*
> > 	 * now the shrinker is fully set up, take the first
> > 	 * reference to it to indicate that lookup operations are
> > 	 * now allowed to use it via shrinker_try_get().
> > 	 */
> > 	refcount_set(&shrinker->refcount, 1);
> > }
> > 
> > > diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
> > > index f1becfd45853..c5573066adbf 100644
> > > --- a/mm/shrinker_debug.c
> > > +++ b/mm/shrinker_debug.c
> > > @@ -5,6 +5,7 @@
> > >   #include <linux/seq_file.h>
> > >   #include <linux/shrinker.h>
> > >   #include <linux/memcontrol.h>
> > > +#include <linux/rculist.h>
> > >   /* defined in vmscan.c */
> > >   extern struct rw_semaphore shrinker_rwsem;
> > > @@ -161,17 +162,21 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
> > >   {
> > >   	struct dentry *entry;
> > >   	char buf[128];
> > > -	int id;
> > > -
> > > -	lockdep_assert_held(&shrinker_rwsem);
> > > +	int id, ret = 0;
> > >   	/* debugfs isn't initialized yet, add debugfs entries later. */
> > >   	if (!shrinker_debugfs_root)
> > >   		return 0;
> > > +	down_write(&shrinker_rwsem);
> > > +	if (shrinker->debugfs_entry)
> > > +		goto fail;
> > > +
> > >   	id = ida_alloc(&shrinker_debugfs_ida, GFP_KERNEL);
> > > -	if (id < 0)
> > > -		return id;
> > > +	if (id < 0) {
> > > +		ret = id;
> > > +		goto fail;
> > > +	}
> > >   	shrinker->debugfs_id = id;
> > >   	snprintf(buf, sizeof(buf), "%s-%d", shrinker->name, id);
> > > @@ -180,7 +185,8 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
> > >   	entry = debugfs_create_dir(buf, shrinker_debugfs_root);
> > >   	if (IS_ERR(entry)) {
> > >   		ida_free(&shrinker_debugfs_ida, id);
> > > -		return PTR_ERR(entry);
> > > +		ret = PTR_ERR(entry);
> > > +		goto fail;
> > >   	}
> > >   	shrinker->debugfs_entry = entry;
> > > @@ -188,7 +194,10 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
> > >   			    &shrinker_debugfs_count_fops);
> > >   	debugfs_create_file("scan", 0220, entry, shrinker,
> > >   			    &shrinker_debugfs_scan_fops);
> > > -	return 0;
> > > +
> > > +fail:
> > > +	up_write(&shrinker_rwsem);
> > > +	return ret;
> > >   }
> > >   int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
> > > @@ -243,6 +252,11 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
> > >   	shrinker->name = NULL;
> > >   	*debugfs_id = entry ? shrinker->debugfs_id : -1;
> > > +	/*
> > > +	 * Ensure that shrinker->registered has been set to false before
> > > +	 * shrinker->debugfs_entry is set to NULL.
> > > +	 */
> > > +	smp_wmb();
> > >   	shrinker->debugfs_entry = NULL;
> > >   	return entry;
> > > @@ -266,14 +280,26 @@ static int __init shrinker_debugfs_init(void)
> > >   	shrinker_debugfs_root = dentry;
> > >   	/* Create debugfs entries for shrinkers registered at boot */
> > > -	down_write(&shrinker_rwsem);
> > > -	list_for_each_entry(shrinker, &shrinker_list, list)
> > > +	rcu_read_lock();
> > > +	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
> > > +		if (!shrinker_try_get(shrinker))
> > > +			continue;
> > > +		rcu_read_unlock();
> > > +
> > >   		if (!shrinker->debugfs_entry) {
> > > -			ret = shrinker_debugfs_add(shrinker);
> > > -			if (ret)
> > > -				break;
> > > +			/* Paired with smp_wmb() in shrinker_debugfs_detach() */
> > > +			smp_rmb();
> > > +			if (READ_ONCE(shrinker->registered))
> > > +				ret = shrinker_debugfs_add(shrinker);
> > >   		}
> > > -	up_write(&shrinker_rwsem);
> > > +
> > > +		rcu_read_lock();
> > > +		shrinker_put(shrinker);
> > > +
> > > +		if (ret)
> > > +			break;
> > > +	}
> > > +	rcu_read_unlock();
> > >   	return ret;
> > >   }
> > 
> > And all this churn and complexity can go away because the
> > shrinker_rwsem is still used to protect shrinker_register()
> > entirely....
> 
> My consideration is that during this process, there may be a
> driver probe failure and then shrinker_free() is called (the
> shrinker_debugfs_init() is called in late_initcall stage). In
> this case, we need to use RCU+refcount to ensure that the shrinker
> is not freed.

Yeah, you're trying to work around the lack of a
wait_for_completion() call in shrinker_free().

With that, this doesn't need RCU at all, and the iteration can be
done fully under the shrinker_rwsem() safely and so none of this
code needs to change.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH v2 44/47] mm: shrinker: make global slab shrink lockless

[Qi Zheng]

Hi Dave,

On 2023/7/27 07:09, Dave Chinner wrote:
> On Wed, Jul 26, 2023 at 05:14:09PM +0800, Qi Zheng wrote:
>> On 2023/7/26 16:08, Dave Chinner wrote:
>>> On Mon, Jul 24, 2023 at 05:43:51PM +0800, Qi Zheng wrote:
>>>> @@ -122,6 +126,13 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
>>>>    void shrinker_register(struct shrinker *shrinker);
>>>>    void shrinker_unregister(struct shrinker *shrinker);
>>>> +static inline bool shrinker_try_get(struct shrinker *shrinker)
>>>> +{
>>>> +	return READ_ONCE(shrinker->registered) &&
>>>> +	       refcount_inc_not_zero(&shrinker->refcount);
>>>> +}
>>>
>>> Why do we care about shrinker->registered here? If we don't set
>>> the refcount to 1 until we have fully initialised everything, then
>>> the shrinker code can key entirely off the reference count and
>>> none of the lookup code needs to care about whether the shrinker is
>>> registered or not.
>>
>> The purpose of checking shrinker->registered here is to stop running
>> shrinker after calling shrinker_free(), which can prevent the following
>> situations from happening:
>>
>> CPU 0                 CPU 1
>>
>> shrinker_try_get()
>>
>>                         shrinker_try_get()
>>
>> shrinker_put()
>> shrinker_try_get()
>>                         shrinker_put()
> 
> I don't see any race here? What is wrong with having multiple active
> users at once?

Maybe I'm overthinking. What I think is that if there are multiple users
at once, it may cause the above-mentioned livelock, which will cause
shrinker_free() to wait for a long time. But this probability should be
very low.

> 
>>>
>>> This should use a completion, then it is always safe under
>>> rcu_read_lock().  This also gets rid of the shrinker_lock spin lock,
>>> which only exists because we can't take a blocking lock under
>>> rcu_read_lock(). i.e:
>>>
>>>
>>> void shrinker_put(struct shrinker *shrinker)
>>> {
>>> 	if (refcount_dec_and_test(&shrinker->refcount))
>>> 		complete(&shrinker->done);
>>> }
>>>
>>> void shrinker_free()
>>> {
>>> 	.....
>>> 	refcount_dec(&shrinker->refcount);
>>
>> I guess what you mean is shrinker_put(), because here may be the last
>> refcount.
> 
> Yes, I did.
> 
>>> 	wait_for_completion(&shrinker->done);
>>> 	/*
>>> 	 * lookups on the shrinker will now all fail as refcount has
>>> 	 * fallen to zero. We can now remove it from the lists and
>>> 	 * free it.
>>> 	 */
>>> 	down_write(shrinker_rwsem);
>>> 	list_del_rcu(&shrinker->list);
>>> 	up_write(&shrinker_rwsem);
>>> 	call_rcu(shrinker->rcu_head, shrinker_free_rcu_cb);
>>> }
>>>
>>> ....
>>>
>>>> @@ -686,11 +711,14 @@ EXPORT_SYMBOL(shrinker_free_non_registered);
>>>>    void shrinker_register(struct shrinker *shrinker)
>>>>    {
>>>> -	down_write(&shrinker_rwsem);
>>>> -	list_add_tail(&shrinker->list, &shrinker_list);
>>>> -	shrinker->flags |= SHRINKER_REGISTERED;
>>>> +	refcount_set(&shrinker->refcount, 1);
>>>> +
>>>> +	spin_lock(&shrinker_lock);
>>>> +	list_add_tail_rcu(&shrinker->list, &shrinker_list);
>>>> +	spin_unlock(&shrinker_lock);
>>>> +
>>>>    	shrinker_debugfs_add(shrinker);
>>>> -	up_write(&shrinker_rwsem);
>>>> +	WRITE_ONCE(shrinker->registered, true);
>>>>    }
>>>>    EXPORT_SYMBOL(shrinker_register);
>>>
>>> This just looks wrong - you are trying to use WRITE_ONCE() as a
>>> release barrier to indicate that the shrinker is now set up fully.
>>> That's not necessary - the refcount is an atomic and along with the
>>> rcu locks they should provides all the barriers we need. i.e.
>>
>> The reason I used WRITE_ONCE() here is because the shrinker->registered
>> will be read and written concurrently (read in shrinker_try_get() and
>> written in shrinker_free()), which is why I added shrinker::registered
>> field instead of using SHRINKER_REGISTERED flag (this can reduce the
>> addition of WRITE_ONCE()/READ_ONCE()).
> 
> Using WRITE_ONCE/READ_ONCE doesn't provide memory barriers needed to
> use the field like this. You need release/acquire memory ordering
> here. i.e. smp_store_release()/smp_load_acquire().
> 
> As it is, the refcount_inc_not_zero() provides a control dependency,
> as documented in include/linux/refcount.h, refcount_dec_and_test()
> provides release memory ordering. The only thing I think we may need
> is a write barrier before refcount_set(), such that if
> refcount_inc_not_zero() sees a non-zero value, it is guaranteed to
> see an initialised structure...
> 
> i.e. refcounts provide all the existence and initialisation
> guarantees. Hence I don't see the need to use shrinker->registered
> like this and it can remain a bit flag protected by the
> shrinker_rwsem().

Ah, I didn't consider the memory order with refcount when I added
WRITE_ONCE/READ_ONCE to shrinker->registered, just didn't want KCSAN
to complain (there are multiple visitors at the same time, one of which
is a writer).

And the livelock case mentioned above is indeed unlikely to happen, so
I will delete shrinker->registered in the next version.

> 
> 
>>> void shrinker_register(struct shrinker *shrinker)
>>> {
>>> 	down_write(&shrinker_rwsem);
>>> 	list_add_tail_rcu(&shrinker->list, &shrinker_list);
>>> 	shrinker->flags |= SHRINKER_REGISTERED;
>>> 	shrinker_debugfs_add(shrinker);
>>> 	up_write(&shrinker_rwsem);
>>>
>>> 	/*
>>> 	 * now the shrinker is fully set up, take the first
>>> 	 * reference to it to indicate that lookup operations are
>>> 	 * now allowed to use it via shrinker_try_get().
>>> 	 */
>>> 	refcount_set(&shrinker->refcount, 1);
>>> }
>>>
>>>> diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
>>>> index f1becfd45853..c5573066adbf 100644
>>>> --- a/mm/shrinker_debug.c
>>>> +++ b/mm/shrinker_debug.c
>>>> @@ -5,6 +5,7 @@
>>>>    #include <linux/seq_file.h>
>>>>    #include <linux/shrinker.h>
>>>>    #include <linux/memcontrol.h>
>>>> +#include <linux/rculist.h>
>>>>    /* defined in vmscan.c */
>>>>    extern struct rw_semaphore shrinker_rwsem;
>>>> @@ -161,17 +162,21 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>>>>    {
>>>>    	struct dentry *entry;
>>>>    	char buf[128];
>>>> -	int id;
>>>> -
>>>> -	lockdep_assert_held(&shrinker_rwsem);
>>>> +	int id, ret = 0;
>>>>    	/* debugfs isn't initialized yet, add debugfs entries later. */
>>>>    	if (!shrinker_debugfs_root)
>>>>    		return 0;
>>>> +	down_write(&shrinker_rwsem);
>>>> +	if (shrinker->debugfs_entry)
>>>> +		goto fail;
>>>> +
>>>>    	id = ida_alloc(&shrinker_debugfs_ida, GFP_KERNEL);
>>>> -	if (id < 0)
>>>> -		return id;
>>>> +	if (id < 0) {
>>>> +		ret = id;
>>>> +		goto fail;
>>>> +	}
>>>>    	shrinker->debugfs_id = id;
>>>>    	snprintf(buf, sizeof(buf), "%s-%d", shrinker->name, id);
>>>> @@ -180,7 +185,8 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>>>>    	entry = debugfs_create_dir(buf, shrinker_debugfs_root);
>>>>    	if (IS_ERR(entry)) {
>>>>    		ida_free(&shrinker_debugfs_ida, id);
>>>> -		return PTR_ERR(entry);
>>>> +		ret = PTR_ERR(entry);
>>>> +		goto fail;
>>>>    	}
>>>>    	shrinker->debugfs_entry = entry;
>>>> @@ -188,7 +194,10 @@ int shrinker_debugfs_add(struct shrinker *shrinker)
>>>>    			    &shrinker_debugfs_count_fops);
>>>>    	debugfs_create_file("scan", 0220, entry, shrinker,
>>>>    			    &shrinker_debugfs_scan_fops);
>>>> -	return 0;
>>>> +
>>>> +fail:
>>>> +	up_write(&shrinker_rwsem);
>>>> +	return ret;
>>>>    }
>>>>    int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
>>>> @@ -243,6 +252,11 @@ struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
>>>>    	shrinker->name = NULL;
>>>>    	*debugfs_id = entry ? shrinker->debugfs_id : -1;
>>>> +	/*
>>>> +	 * Ensure that shrinker->registered has been set to false before
>>>> +	 * shrinker->debugfs_entry is set to NULL.
>>>> +	 */
>>>> +	smp_wmb();
>>>>    	shrinker->debugfs_entry = NULL;
>>>>    	return entry;
>>>> @@ -266,14 +280,26 @@ static int __init shrinker_debugfs_init(void)
>>>>    	shrinker_debugfs_root = dentry;
>>>>    	/* Create debugfs entries for shrinkers registered at boot */
>>>> -	down_write(&shrinker_rwsem);
>>>> -	list_for_each_entry(shrinker, &shrinker_list, list)
>>>> +	rcu_read_lock();
>>>> +	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
>>>> +		if (!shrinker_try_get(shrinker))
>>>> +			continue;
>>>> +		rcu_read_unlock();
>>>> +
>>>>    		if (!shrinker->debugfs_entry) {
>>>> -			ret = shrinker_debugfs_add(shrinker);
>>>> -			if (ret)
>>>> -				break;
>>>> +			/* Paired with smp_wmb() in shrinker_debugfs_detach() */
>>>> +			smp_rmb();
>>>> +			if (READ_ONCE(shrinker->registered))
>>>> +				ret = shrinker_debugfs_add(shrinker);
>>>>    		}
>>>> -	up_write(&shrinker_rwsem);
>>>> +
>>>> +		rcu_read_lock();
>>>> +		shrinker_put(shrinker);
>>>> +
>>>> +		if (ret)
>>>> +			break;
>>>> +	}
>>>> +	rcu_read_unlock();
>>>>    	return ret;
>>>>    }
>>>
>>> And all this churn and complexity can go away because the
>>> shrinker_rwsem is still used to protect shrinker_register()
>>> entirely....
>>
>> My consideration is that during this process, there may be a
>> driver probe failure and then shrinker_free() is called (the
>> shrinker_debugfs_init() is called in late_initcall stage). In
>> this case, we need to use RCU+refcount to ensure that the shrinker
>> is not freed.
> 
> Yeah, you're trying to work around the lack of a
> wait_for_completion() call in shrinker_free().
> 
> With that, this doesn't need RCU at all, and the iteration can be
> done fully under the shrinker_rwsem() safely and so none of this
> code needs to change.

Oh, indeed, here does not need to be changed.

Thanks,
Qi

> 
> Cheers,
> 
> Dave.