[PATCH v3 0/4] cleanups for lockless slab shrink

[PATCH v3 0/4] cleanups for lockless slab shrink

[Qi Zheng]

Hi all,

This series is some cleanups split from the previous patchset[1], I dropped the
[PATCH v2 5/5] which is more related to the main lockless patch.

This series is based on the next-20230823.

Comments and suggestions are welcome.

[1]. https://lore.kernel.org/lkml/20230807110936.21819-1-zhengqi.arch@bytedance.com/

Thanks,
Qi

Changlog in part 1 v2 -> part 1 v3:
 - drop [PATCH v2 5/5]
 - collect Acked-by
 - rebase onto the next-20230823

Changlog in part 1 v1 -> part 1 v2:
 - fix compilation warning in [PATCH 1/5]
 - rename synchronize_shrinkers() to ttm_pool_synchronize_shrinkers()
   (pointed by Christian König)
 - collect Reviewed-by

Changlog in v4 -> part 1 v1:
 - split from the previous large patchset
 - fix comment format in [PATCH v4 01/48] (pointed by Muchun Song)
 - change to use kzalloc_node() and fix typo in [PATCH v4 44/48]
   (pointed by Dave Chinner)
 - collect Reviewed-bys
 - rebase onto the next-20230815

Qi Zheng (4):
  mm: move some shrinker-related function declarations to mm/internal.h
  mm: vmscan: move shrinker-related code into a separate file
  mm: shrinker: remove redundant shrinker_rwsem in debugfs operations
  drm/ttm: introduce pool_shrink_rwsem

 drivers/gpu/drm/ttm/ttm_pool.c |  17 +-
 include/linux/shrinker.h       |  20 -
 mm/Makefile                    |   4 +-
 mm/internal.h                  |  28 ++
 mm/shrinker.c                  | 694 ++++++++++++++++++++++++++++++++
 mm/shrinker_debug.c            |  18 +-
 mm/vmscan.c                    | 701 ---------------------------------
 7 files changed, 743 insertions(+), 739 deletions(-)
 create mode 100644 mm/shrinker.c

-- 
2.30.2

[PATCH v3 1/4] mm: move some shrinker-related function declarations to mm/internal.h

[Qi Zheng]

The following functions are only used inside the mm subsystem, so it's
better to move their declarations to the mm/internal.h file.

1. shrinker_debugfs_add()
2. shrinker_debugfs_detach()
3. shrinker_debugfs_remove()

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/shrinker.h | 19 -------------------
 mm/internal.h            | 26 ++++++++++++++++++++++++++
 mm/shrinker_debug.c      |  2 ++
 3 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 224293b2dd06..8dc15aa37410 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -106,28 +106,9 @@ extern void free_prealloced_shrinker(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,
-					      int *debugfs_id);
-extern void shrinker_debugfs_remove(struct dentry *debugfs_entry,
-				    int debugfs_id);
 extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
 						  const char *fmt, ...);
 #else /* CONFIG_SHRINKER_DEBUG */
-static inline int shrinker_debugfs_add(struct shrinker *shrinker)
-{
-	return 0;
-}
-static inline struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
-						     int *debugfs_id)
-{
-	*debugfs_id = -1;
-	return NULL;
-}
-static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
-					   int debugfs_id)
-{
-}
 static inline __printf(2, 3)
 int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
 {
diff --git a/mm/internal.h b/mm/internal.h
index 7499b5ea1cf6..f30bb60e7790 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1155,4 +1155,30 @@ struct vma_prepare {
 	struct vm_area_struct *remove;
 	struct vm_area_struct *remove2;
 };
+
+/* shrinker related functions */
+
+#ifdef CONFIG_SHRINKER_DEBUG
+extern int shrinker_debugfs_add(struct shrinker *shrinker);
+extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
+					      int *debugfs_id);
+extern void shrinker_debugfs_remove(struct dentry *debugfs_entry,
+				    int debugfs_id);
+#else /* CONFIG_SHRINKER_DEBUG */
+static inline int shrinker_debugfs_add(struct shrinker *shrinker)
+{
+	return 0;
+}
+static inline struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
+						     int *debugfs_id)
+{
+	*debugfs_id = -1;
+	return NULL;
+}
+static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
+					   int debugfs_id)
+{
+}
+#endif /* CONFIG_SHRINKER_DEBUG */
+
 #endif	/* __MM_INTERNAL_H */
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 3ab53fad8876..ee0cddb4530f 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -6,6 +6,8 @@
 #include <linux/shrinker.h>
 #include <linux/memcontrol.h>
 
+#include "internal.h"
+
 /* defined in vmscan.c */
 extern struct rw_semaphore shrinker_rwsem;
 extern struct list_head shrinker_list;
-- 
2.30.2

[PATCH v3 2/4] 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>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/Makefile   |   4 +-
 mm/internal.h |   2 +
 mm/shrinker.c | 709 ++++++++++++++++++++++++++++++++++++++++++++++++++
 mm/vmscan.c   | 701 -------------------------------------------------
 4 files changed, 713 insertions(+), 703 deletions(-)
 create mode 100644 mm/shrinker.c

diff --git a/mm/Makefile b/mm/Makefile
index ec65984e2ade..33873c8aedb3 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 shmem_quota.o\
 			   interval_tree.o list_lru.o workingset.o \
diff --git a/mm/internal.h b/mm/internal.h
index f30bb60e7790..5d4697612073 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1157,6 +1157,8 @@ struct vma_prepare {
 };
 
 /* shrinker related functions */
+unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
+			  int priority);
 
 #ifdef CONFIG_SHRINKER_DEBUG
 extern int shrinker_debugfs_add(struct shrinker *shrinker);
diff --git a/mm/shrinker.c b/mm/shrinker.c
new file mode 100644
index 000000000000..043c87ccfab4
--- /dev/null
+++ b/mm/shrinker.c
@@ -0,0 +1,709 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/memcontrol.h>
+#include <linux/rwsem.h>
+#include <linux/shrinker.h>
+#include <trace/events/vmscan.h>
+
+#include "internal.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 6f13394b112e..62bbfea11835 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 v3 3/4] 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>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/shrinker_debug.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index ee0cddb4530f..e4ce509f619e 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -51,17 +51,12 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
 	struct mem_cgroup *memcg;
 	unsigned long total;
 	bool memcg_aware;
-	int ret, nid;
+	int ret = 0, nid;
 
 	count_per_node = kcalloc(nr_node_ids, sizeof(unsigned long), GFP_KERNEL);
 	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;
@@ -94,7 +89,6 @@ 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;
@@ -119,7 +113,6 @@ 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))
@@ -148,12 +141,6 @@ 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;
@@ -161,7 +148,6 @@ 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 v3 4/4] 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
ttm_pool_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>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/ttm/ttm_pool.c | 17 ++++++++++++++++-
 include/linux/shrinker.h       |  1 -
 mm/shrinker.c                  | 15 ---------------
 3 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index cddb9151d20f..648ca70403a7 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);
 
+/**
+ * ttm_pool_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 ttm_pool_synchronize_shrinkers(void)
+{
+	down_write(&pool_shrink_rwsem);
+	up_write(&pool_shrink_rwsem);
+}
+
 /**
  * ttm_pool_fini - Cleanup a pool
  *
@@ -593,7 +608,7 @@ void ttm_pool_fini(struct ttm_pool *pool)
 	/* We removed the pool types from the LRU, but we need to also make sure
 	 * that no shrinker is concurrently freeing pages from the pool.
 	 */
-	synchronize_shrinkers();
+	ttm_pool_synchronize_shrinkers();
 }
 EXPORT_SYMBOL(ttm_pool_fini);
 
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 8dc15aa37410..6b5843c3b827 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -103,7 +103,6 @@ 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
 extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 043c87ccfab4..a16cd448b924 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -692,18 +692,3 @@ void unregister_shrinker(struct shrinker *shrinker)
 	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);
-- 
2.30.2

Re: [PATCH v3 0/4] cleanups for lockless slab shrink

[Qi Zheng]

On 2023/8/24 11:35, Qi Zheng wrote:
> Hi all,
> 
> This series is some cleanups split from the previous patchset[1], I dropped the
> [PATCH v2 5/5] which is more related to the main lockless patch.
> 
> This series is based on the next-20230823.
> 
> Comments and suggestions are welcome.
> 
> [1]. https://lore.kernel.org/lkml/20230807110936.21819-1-zhengqi.arch@bytedance.com/
> 
> Thanks,
> Qi
> 
> Changlog in part 1 v2 -> part 1 v3:
>   - drop [PATCH v2 5/5]
>   - collect Acked-by
>   - rebase onto the next-20230823

Hi Andrew,

Can this cleanup series be merged? This part is relatively independent
and has Reviewed-bys and Acked-by.

Thanks,
Qi

> 
> Changlog in part 1 v1 -> part 1 v2:
>   - fix compilation warning in [PATCH 1/5]
>   - rename synchronize_shrinkers() to ttm_pool_synchronize_shrinkers()
>     (pointed by Christian König)
>   - collect Reviewed-by
> 
> Changlog in v4 -> part 1 v1:
>   - split from the previous large patchset
>   - fix comment format in [PATCH v4 01/48] (pointed by Muchun Song)
>   - change to use kzalloc_node() and fix typo in [PATCH v4 44/48]
>     (pointed by Dave Chinner)
>   - collect Reviewed-bys
>   - rebase onto the next-20230815
> 
> Qi Zheng (4):
>    mm: move some shrinker-related function declarations to mm/internal.h
>    mm: vmscan: move shrinker-related code into a separate file
>    mm: shrinker: remove redundant shrinker_rwsem in debugfs operations
>    drm/ttm: introduce pool_shrink_rwsem
> 
>   drivers/gpu/drm/ttm/ttm_pool.c |  17 +-
>   include/linux/shrinker.h       |  20 -
>   mm/Makefile                    |   4 +-
>   mm/internal.h                  |  28 ++
>   mm/shrinker.c                  | 694 ++++++++++++++++++++++++++++++++
>   mm/shrinker_debug.c            |  18 +-
>   mm/vmscan.c                    | 701 ---------------------------------
>   7 files changed, 743 insertions(+), 739 deletions(-)
>   create mode 100644 mm/shrinker.c
>