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* [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware
@ 2021-03-11 19:08 Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 01/13] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
                   ` (12 more replies)
  0 siblings, 13 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel


Changelog
v9 --> v10:
    * Rebased onto next-20210310 of linux-next to solve the conflict with
      "mm: memcontrol: switch to rstat" series. 
v8 --> v9:
    * Used two parameters form of kvfree_rcu() per Shakeel.
    * Amended commit log about allocating shrinker_info for root memcg for
      patch 09/13 per Shakeel.
    * Colleted more ack and review tags.
    * Rebased onto 5.12-rc2.
v7 --> v8:
    * Added lockdep assert in expand_shrinker_info() per Roman.
    * Added patch 05/13 to use kvfree_rcu() instead of call_rcu() per Roman
      and Kirill.
    * Moved rwsem acquire/release out of unregister_memcg_shrinker() per Roman.
    * Renamed count_nr_deferred_{memcg} to xchg_nr_deferred_{memcg} per Roman.
    * Fixed the next_deferred logic per Vlastimil.
    * Misc minor code cleanup, refactor and spelling correction per Roman
      and Shakeel.
    * Collected more ack and review tags from Roman, Shakeel and Vlastimil.
v6 --> v7:
    * Expanded shrinker_info in a batch of BITS_PER_LONG per Kirill.
    * Added patch 06/12 to introduce a helper for dereferencing shrinker_info
      per Kirill.
    * Renamed set_nr_deferred_memcg to add_nr_deferred_memcg per Kirill.
    * Collected Acked-by from Kirill.
v5 --> v6:
    * Rebased on top of https://lore.kernel.org/linux-mm/1611216029-34397-1-git-send-email-abaci-bugfix@linux.alibaba.com/
      per Kirill.
    * Don't register shrinker idr with NULL and remove idr_replace() per Vlastimil.
    * Move nr_deferred before map to guarantee the alignment per Vlastimil.
    * Misc minor code cleanup and refactor per Kirill and Vlastimil.
    * Added Acked-by from Vlastimil for path #1, #2, #3, #5, #9 and #10.
v4 --> v5:
    * Incorporated the comments from Kirill.
    * Rebased to v5.11-rc5.
v3 --> v4:
    * Removed "memcg_" prefix for shrinker_maps related functions per Roman.
    * Use write lock instead of read lock per Kirill. Also removed Johannes's ack
      since write lock is used.
    * Incorporated the comments from Kirill.
    * Removed RFC.
    * Rebased to v5.11-rc4.
v2 --> v3:
    * Moved shrinker_maps related code to vmscan.c per Dave.
    * Removed memcg_shrinker_map_size. Calcuated the size of map via shrinker_nr_max
      per Johannes.
    * Consolidated shrinker_deferred with shrinker_maps into one struct per Dave.
    * Simplified the nr_deferred related code.
    * Dropped the memory barrier from v2.
    * Moved nr_deferred reparent code to vmscan.c per Dave.
    * Added test coverage information in patch #11. Dave is concerned about the
      potential regression. I didn't notice regression with my tests, but suggestions
      about more test coverage is definitely welcome. And it may help spot regression
      with this patch in -mm tree then linux-next tree so I keep it in this version.
    * The code cleanup and consolidation resulted in the series grow to 11 patches.
    * Rebased onto 5.11-rc2. 
v1 --> v2:
    * Use shrinker->flags to store the new SHRINKER_REGISTERED flag per Roman.
    * Folded patch #1 into patch #6 per Roman.
    * Added memory barrier to prevent shrink_slab_memcg from seeing NULL shrinker_maps/
      shrinker_deferred per Kirill.
    * Removed memcg_shrinker_map_mutex. Protcted shrinker_map/shrinker_deferred
      allocations from expand with shrinker_rwsem per Johannes.

Recently huge amount one-off slab drop was seen on some vfs metadata heavy workloads,
it turned out there were huge amount accumulated nr_deferred objects seen by the
shrinker.

On our production machine, I saw absurd number of nr_deferred shown as the below
tracing result: 

<...>-48776 [032] .... 27970562.458916: mm_shrink_slab_start:
super_cache_scan+0x0/0x1a0 ffff9a83046f3458: nid: 0 objects to shrink
2531805877005 gfp_flags GFP_HIGHUSER_MOVABLE pgs_scanned 32 lru_pgs
9300 cache items 1667 delta 11 total_scan 833

There are 2.5 trillion deferred objects on one node, assuming all of them
are dentry (192 bytes per object), so the total size of deferred on
one node is ~480TB. It is definitely ridiculous.

I managed to reproduce this problem with kernel build workload plus negative dentry
generator.

First step, run the below kernel build test script:

NR_CPUS=`cat /proc/cpuinfo | grep -e processor | wc -l`

cd /root/Buildarea/linux-stable

for i in `seq 1500`; do
        cgcreate -g memory:kern_build
        echo 4G > /sys/fs/cgroup/memory/kern_build/memory.limit_in_bytes

        echo 3 > /proc/sys/vm/drop_caches
        cgexec -g memory:kern_build make clean > /dev/null 2>&1
        cgexec -g memory:kern_build make -j$NR_CPUS > /dev/null 2>&1

        cgdelete -g memory:kern_build
done

Then run the below negative dentry generator script:

NR_CPUS=`cat /proc/cpuinfo | grep -e processor | wc -l`

mkdir /sys/fs/cgroup/memory/test
echo $$ > /sys/fs/cgroup/memory/test/tasks

for i in `seq $NR_CPUS`; do
        while true; do
                FILE=`head /dev/urandom | tr -dc A-Za-z0-9 | head -c 64`
                cat $FILE 2>/dev/null
        done &
done

Then kswapd will shrink half of dentry cache in just one loop as the below tracing result
showed:

	kswapd0-475   [028] .... 305968.252561: mm_shrink_slab_start: super_cache_scan+0x0/0x190 0000000024acf00c: nid: 0
objects to shrink 4994376020 gfp_flags GFP_KERNEL cache items 93689873 delta 45746 total_scan 46844936 priority 12
	kswapd0-475   [021] .... 306013.099399: mm_shrink_slab_end: super_cache_scan+0x0/0x190 0000000024acf00c: nid: 0 unused
scan count 4994376020 new scan count 4947576838 total_scan 8 last shrinker return val 46844928

There were huge number of deferred objects before the shrinker was called, the behavior
does match the code but it might be not desirable from the user's stand of point.

The excessive amount of nr_deferred might be accumulated due to various reasons, for example:
    * GFP_NOFS allocation
    * Significant times of small amount scan (< scan_batch, 1024 for vfs metadata)

However the LRUs of slabs are per memcg (memcg-aware shrinkers) but the deferred objects
is per shrinker, this may have some bad effects:
    * Poor isolation among memcgs. Some memcgs which happen to have frequent limit
      reclaim may get nr_deferred accumulated to a huge number, then other innocent
      memcgs may take the fall. In our case the main workload was hit.
    * Unbounded deferred objects. There is no cap for deferred objects, it can outgrow
      ridiculously as the tracing result showed.
    * Easy to get out of control. Although shrinkers take into account deferred objects,
      but it can go out of control easily. One misconfigured memcg could incur absurd 
      amount of deferred objects in a period of time.
    * Sort of reclaim problems, i.e. over reclaim, long reclaim latency, etc. There may be
      hundred GB slab caches for vfe metadata heavy workload, shrink half of them may take
      minutes. We observed latency spike due to the prolonged reclaim.

These issues also have been discussed in https://lore.kernel.org/linux-mm/20200916185823.5347-1-shy828301@gmail.com/.
The patchset is the outcome of that discussion.

So this patchset makes nr_deferred per-memcg to tackle the problem. It does:
    * Have memcg_shrinker_deferred per memcg per node, just like what shrinker_map
      does. Instead it is an atomic_long_t array, each element represent one shrinker
      even though the shrinker is not memcg aware, this simplifies the implementation.
      For memcg aware shrinkers, the deferred objects are just accumulated to its own
      memcg. The shrinkers just see nr_deferred from its own memcg. Non memcg aware
      shrinkers still use global nr_deferred from struct shrinker.
    * Once the memcg is offlined, its nr_deferred will be reparented to its parent along
      with LRUs.
    * The root memcg has memcg_shrinker_deferred array too. It simplifies the handling of
      reparenting to root memcg.
    * Cap nr_deferred to 2x of the length of lru. The idea is borrowed from Dave Chinner's
      series (https://lore.kernel.org/linux-xfs/20191031234618.15403-1-david@fromorbit.com/)

The downside is each memcg has to allocate extra memory to store the nr_deferred array.
On our production environment, there are typically around 40 shrinkers, so each memcg
needs ~320 bytes. 10K memcgs would need ~3.2MB memory. It seems fine.

We have been running the patched kernel on some hosts of our fleet (test and production) for
months, it works very well. The monitor data shows the working set is sustained as expected.

Yang Shi (13):
      mm: vmscan: use nid from shrink_control for tracepoint
      mm: vmscan: consolidate shrinker_maps handling code
      mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation
      mm: vmscan: remove memcg_shrinker_map_size
      mm: vmscan: use kvfree_rcu instead of call_rcu
      mm: memcontrol: rename shrinker_map to shrinker_info
      mm: vmscan: add shrinker_info_protected() helper
      mm: vmscan: use a new flag to indicate shrinker is registered
      mm: vmscan: add per memcg shrinker nr_deferred
      mm: vmscan: use per memcg nr_deferred of shrinker
      mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers
      mm: memcontrol: reparent nr_deferred when memcg offline
      mm: vmscan: shrink deferred objects proportional to priority

 include/linux/memcontrol.h |  23 +++---
 include/linux/shrinker.h   |   7 +-
 mm/huge_memory.c           |   4 +-
 mm/list_lru.c              |   6 +-
 mm/memcontrol.c            | 130 +------------------------------
 mm/vmscan.c                | 394 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------------------------
 6 files changed, 319 insertions(+), 245 deletions(-)


^ permalink raw reply	[flat|nested] 14+ messages in thread

* [v10 PATCH 01/13] mm: vmscan: use nid from shrink_control for tracepoint
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 02/13] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
                   ` (11 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

The tracepoint's nid should show what node the shrink happens on, the start tracepoint
uses nid from shrinkctl, but the nid might be set to 0 before end tracepoint if the
shrinker is not NUMA aware, so the tracing log may show the shrink happens on one
node but end up on the other node.  It seems confusing.  And the following patch
will remove using nid directly in do_shrink_slab(), this patch also helps cleanup
the code.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 407051ebe869..bdc32c803c66 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -536,7 +536,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	else
 		new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
 
-	trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
+	trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
 	return freed;
 }
 
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 02/13] mm: vmscan: consolidate shrinker_maps handling code
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 01/13] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 03/13] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
                   ` (10 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

The shrinker map management is not purely memcg specific, it is at the intersection
between memory cgroup and shrinkers.  It's allocation and assignment of a structure,
and the only memcg bit is the map is being stored in a memcg structure.  So move the
shrinker_maps handling code into vmscan.c for tighter integration with shrinker code,
and remove the "memcg_" prefix.  There is no functional change.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/memcontrol.h |  11 ++--
 mm/huge_memory.c           |   4 +-
 mm/list_lru.c              |   6 +-
 mm/memcontrol.c            | 130 +-----------------------------------
 mm/vmscan.c                | 132 ++++++++++++++++++++++++++++++++++++-
 5 files changed, 142 insertions(+), 141 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e946c96daa32..b07dc2d5014d 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1533,10 +1533,9 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
 	return false;
 }
 
-extern int memcg_expand_shrinker_maps(int new_id);
-
-extern void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
-				   int nid, int shrinker_id);
+int alloc_shrinker_maps(struct mem_cgroup *memcg);
+void free_shrinker_maps(struct mem_cgroup *memcg);
+void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
 #else
 #define mem_cgroup_sockets_enabled 0
 static inline void mem_cgroup_sk_alloc(struct sock *sk) { };
@@ -1546,8 +1545,8 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
 	return false;
 }
 
-static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
-					  int nid, int shrinker_id)
+static inline void set_shrinker_bit(struct mem_cgroup *memcg,
+				    int nid, int shrinker_id)
 {
 }
 #endif
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index bff92dea5ab3..92a1227be029 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2836,8 +2836,8 @@ void deferred_split_huge_page(struct page *page)
 		ds_queue->split_queue_len++;
 #ifdef CONFIG_MEMCG
 		if (memcg)
-			memcg_set_shrinker_bit(memcg, page_to_nid(page),
-					       deferred_split_shrinker.id);
+			set_shrinker_bit(memcg, page_to_nid(page),
+					 deferred_split_shrinker.id);
 #endif
 	}
 	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 6f067b6b935f..cd58790d0fb3 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -125,8 +125,8 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
 		list_add_tail(item, &l->list);
 		/* Set shrinker bit if the first element was added */
 		if (!l->nr_items++)
-			memcg_set_shrinker_bit(memcg, nid,
-					       lru_shrinker_id(lru));
+			set_shrinker_bit(memcg, nid,
+					 lru_shrinker_id(lru));
 		nlru->nr_items++;
 		spin_unlock(&nlru->lock);
 		return true;
@@ -540,7 +540,7 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
 
 	if (src->nr_items) {
 		dst->nr_items += src->nr_items;
-		memcg_set_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));
+		set_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));
 		src->nr_items = 0;
 	}
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index da6fded852df..aeb1847f159c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -402,130 +402,6 @@ DEFINE_STATIC_KEY_FALSE(memcg_kmem_enabled_key);
 EXPORT_SYMBOL(memcg_kmem_enabled_key);
 #endif
 
-static int memcg_shrinker_map_size;
-static DEFINE_MUTEX(memcg_shrinker_map_mutex);
-
-static void memcg_free_shrinker_map_rcu(struct rcu_head *head)
-{
-	kvfree(container_of(head, struct memcg_shrinker_map, rcu));
-}
-
-static int memcg_expand_one_shrinker_map(struct mem_cgroup *memcg,
-					 int size, int old_size)
-{
-	struct memcg_shrinker_map *new, *old;
-	struct mem_cgroup_per_node *pn;
-	int nid;
-
-	lockdep_assert_held(&memcg_shrinker_map_mutex);
-
-	for_each_node(nid) {
-		pn = memcg->nodeinfo[nid];
-		old = rcu_dereference_protected(pn->shrinker_map, true);
-		/* Not yet online memcg */
-		if (!old)
-			return 0;
-
-		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
-		if (!new)
-			return -ENOMEM;
-
-		/* Set all old bits, clear all new bits */
-		memset(new->map, (int)0xff, old_size);
-		memset((void *)new->map + old_size, 0, size - old_size);
-
-		rcu_assign_pointer(pn->shrinker_map, new);
-		call_rcu(&old->rcu, memcg_free_shrinker_map_rcu);
-	}
-
-	return 0;
-}
-
-static void memcg_free_shrinker_maps(struct mem_cgroup *memcg)
-{
-	struct mem_cgroup_per_node *pn;
-	struct memcg_shrinker_map *map;
-	int nid;
-
-	if (mem_cgroup_is_root(memcg))
-		return;
-
-	for_each_node(nid) {
-		pn = memcg->nodeinfo[nid];
-		map = rcu_dereference_protected(pn->shrinker_map, true);
-		kvfree(map);
-		rcu_assign_pointer(pn->shrinker_map, NULL);
-	}
-}
-
-static int memcg_alloc_shrinker_maps(struct mem_cgroup *memcg)
-{
-	struct memcg_shrinker_map *map;
-	int nid, size, ret = 0;
-
-	if (mem_cgroup_is_root(memcg))
-		return 0;
-
-	mutex_lock(&memcg_shrinker_map_mutex);
-	size = memcg_shrinker_map_size;
-	for_each_node(nid) {
-		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
-		if (!map) {
-			memcg_free_shrinker_maps(memcg);
-			ret = -ENOMEM;
-			break;
-		}
-		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map);
-	}
-	mutex_unlock(&memcg_shrinker_map_mutex);
-
-	return ret;
-}
-
-int memcg_expand_shrinker_maps(int new_id)
-{
-	int size, old_size, ret = 0;
-	struct mem_cgroup *memcg;
-
-	size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
-	old_size = memcg_shrinker_map_size;
-	if (size <= old_size)
-		return 0;
-
-	mutex_lock(&memcg_shrinker_map_mutex);
-	if (!root_mem_cgroup)
-		goto unlock;
-
-	for_each_mem_cgroup(memcg) {
-		if (mem_cgroup_is_root(memcg))
-			continue;
-		ret = memcg_expand_one_shrinker_map(memcg, size, old_size);
-		if (ret) {
-			mem_cgroup_iter_break(NULL, memcg);
-			goto unlock;
-		}
-	}
-unlock:
-	if (!ret)
-		memcg_shrinker_map_size = size;
-	mutex_unlock(&memcg_shrinker_map_mutex);
-	return ret;
-}
-
-void memcg_set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
-{
-	if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
-		struct memcg_shrinker_map *map;
-
-		rcu_read_lock();
-		map = rcu_dereference(memcg->nodeinfo[nid]->shrinker_map);
-		/* Pairs with smp mb in shrink_slab() */
-		smp_mb__before_atomic();
-		set_bit(shrinker_id, map->map);
-		rcu_read_unlock();
-	}
-}
-
 /**
  * mem_cgroup_css_from_page - css of the memcg associated with a page
  * @page: page of interest
@@ -5255,11 +5131,11 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 
 	/*
-	 * A memcg must be visible for memcg_expand_shrinker_maps()
+	 * A memcg must be visible for expand_shrinker_maps()
 	 * by the time the maps are allocated. So, we allocate maps
 	 * here, when for_each_mem_cgroup() can't skip it.
 	 */
-	if (memcg_alloc_shrinker_maps(memcg)) {
+	if (alloc_shrinker_maps(memcg)) {
 		mem_cgroup_id_remove(memcg);
 		return -ENOMEM;
 	}
@@ -5323,7 +5199,7 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
 	vmpressure_cleanup(&memcg->vmpressure);
 	cancel_work_sync(&memcg->high_work);
 	mem_cgroup_remove_from_trees(memcg);
-	memcg_free_shrinker_maps(memcg);
+	free_shrinker_maps(memcg);
 	memcg_free_kmem(memcg);
 	mem_cgroup_free(memcg);
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bdc32c803c66..98a44fb81f8a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -185,6 +185,132 @@ static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
 #ifdef CONFIG_MEMCG
+
+static int memcg_shrinker_map_size;
+static DEFINE_MUTEX(memcg_shrinker_map_mutex);
+
+static void free_shrinker_map_rcu(struct rcu_head *head)
+{
+	kvfree(container_of(head, struct memcg_shrinker_map, rcu));
+}
+
+static int expand_one_shrinker_map(struct mem_cgroup *memcg,
+				   int size, int old_size)
+{
+	struct memcg_shrinker_map *new, *old;
+	struct mem_cgroup_per_node *pn;
+	int nid;
+
+	lockdep_assert_held(&memcg_shrinker_map_mutex);
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		old = rcu_dereference_protected(pn->shrinker_map, true);
+		/* Not yet online memcg */
+		if (!old)
+			return 0;
+
+		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
+		if (!new)
+			return -ENOMEM;
+
+		/* Set all old bits, clear all new bits */
+		memset(new->map, (int)0xff, old_size);
+		memset((void *)new->map + old_size, 0, size - old_size);
+
+		rcu_assign_pointer(pn->shrinker_map, new);
+		call_rcu(&old->rcu, free_shrinker_map_rcu);
+	}
+
+	return 0;
+}
+
+void free_shrinker_maps(struct mem_cgroup *memcg)
+{
+	struct mem_cgroup_per_node *pn;
+	struct memcg_shrinker_map *map;
+	int nid;
+
+	if (mem_cgroup_is_root(memcg))
+		return;
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		map = rcu_dereference_protected(pn->shrinker_map, true);
+		kvfree(map);
+		rcu_assign_pointer(pn->shrinker_map, NULL);
+	}
+}
+
+int alloc_shrinker_maps(struct mem_cgroup *memcg)
+{
+	struct memcg_shrinker_map *map;
+	int nid, size, ret = 0;
+
+	if (mem_cgroup_is_root(memcg))
+		return 0;
+
+	mutex_lock(&memcg_shrinker_map_mutex);
+	size = memcg_shrinker_map_size;
+	for_each_node(nid) {
+		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
+		if (!map) {
+			free_shrinker_maps(memcg);
+			ret = -ENOMEM;
+			break;
+		}
+		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map);
+	}
+	mutex_unlock(&memcg_shrinker_map_mutex);
+
+	return ret;
+}
+
+static int expand_shrinker_maps(int new_id)
+{
+	int size, old_size, ret = 0;
+	struct mem_cgroup *memcg;
+
+	size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
+	old_size = memcg_shrinker_map_size;
+	if (size <= old_size)
+		return 0;
+
+	mutex_lock(&memcg_shrinker_map_mutex);
+	if (!root_mem_cgroup)
+		goto unlock;
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		if (mem_cgroup_is_root(memcg))
+			continue;
+		ret = expand_one_shrinker_map(memcg, size, old_size);
+		if (ret) {
+			mem_cgroup_iter_break(NULL, memcg);
+			goto unlock;
+		}
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
+unlock:
+	if (!ret)
+		memcg_shrinker_map_size = size;
+	mutex_unlock(&memcg_shrinker_map_mutex);
+	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 memcg_shrinker_map *map;
+
+		rcu_read_lock();
+		map = rcu_dereference(memcg->nodeinfo[nid]->shrinker_map);
+		/* Pairs with smp mb in shrink_slab() */
+		smp_mb__before_atomic();
+		set_bit(shrinker_id, map->map);
+		rcu_read_unlock();
+	}
+}
+
 /*
  * We allow subsystems to populate their shrinker-related
  * LRU lists before register_shrinker_prepared() is called
@@ -212,7 +338,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 		goto unlock;
 
 	if (id >= shrinker_nr_max) {
-		if (memcg_expand_shrinker_maps(id)) {
+		if (expand_shrinker_maps(id)) {
 			idr_remove(&shrinker_idr, id);
 			goto unlock;
 		}
@@ -590,7 +716,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			 * 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
-			 * memcg_set_shrinker_bit():
+			 * set_shrinker_bit():
 			 *
 			 * list_lru_add()     shrink_slab_memcg()
 			 *   list_add_tail()    clear_bit()
@@ -602,7 +728,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			if (ret == SHRINK_EMPTY)
 				ret = 0;
 			else
-				memcg_set_shrinker_bit(memcg, nid, i);
+				set_shrinker_bit(memcg, nid, i);
 		}
 		freed += ret;
 
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 03/13] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 01/13] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 02/13] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 04/13] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
                   ` (9 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Since memcg_shrinker_map_size just can be changed under holding shrinker_rwsem
exclusively, the read side can be protected by holding read lock, so it sounds
superfluous to have a dedicated mutex.

Kirill Tkhai suggested use write lock since:

  * We want the assignment to shrinker_maps is visible for shrink_slab_memcg().
  * The rcu_dereference_protected() dereferrencing in shrink_slab_memcg(), but
    in case of we use READ lock in alloc_shrinker_maps(), the dereferrencing
    is not actually protected.
  * READ lock makes alloc_shrinker_info() racy against memory allocation fail.
    alloc_shrinker_info()->free_shrinker_info() may free memory right after
    shrink_slab_memcg() dereferenced it. You may say
    shrink_slab_memcg()->mem_cgroup_online() protects us from it? Yes, sure,
    but this is not the thing we want to remember in the future, since this
    spreads modularity.

And a test with heavy paging workload didn't show write lock makes things worse.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 98a44fb81f8a..b08c8d9055ae 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -187,7 +187,6 @@ static DECLARE_RWSEM(shrinker_rwsem);
 #ifdef CONFIG_MEMCG
 
 static int memcg_shrinker_map_size;
-static DEFINE_MUTEX(memcg_shrinker_map_mutex);
 
 static void free_shrinker_map_rcu(struct rcu_head *head)
 {
@@ -201,8 +200,6 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg,
 	struct mem_cgroup_per_node *pn;
 	int nid;
 
-	lockdep_assert_held(&memcg_shrinker_map_mutex);
-
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
 		old = rcu_dereference_protected(pn->shrinker_map, true);
@@ -250,7 +247,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
 	if (mem_cgroup_is_root(memcg))
 		return 0;
 
-	mutex_lock(&memcg_shrinker_map_mutex);
+	down_write(&shrinker_rwsem);
 	size = memcg_shrinker_map_size;
 	for_each_node(nid) {
 		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
@@ -261,7 +258,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
 		}
 		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map);
 	}
-	mutex_unlock(&memcg_shrinker_map_mutex);
+	up_write(&shrinker_rwsem);
 
 	return ret;
 }
@@ -276,9 +273,10 @@ static int expand_shrinker_maps(int new_id)
 	if (size <= old_size)
 		return 0;
 
-	mutex_lock(&memcg_shrinker_map_mutex);
 	if (!root_mem_cgroup)
-		goto unlock;
+		goto out;
+
+	lockdep_assert_held(&shrinker_rwsem);
 
 	memcg = mem_cgroup_iter(NULL, NULL, NULL);
 	do {
@@ -287,13 +285,13 @@ static int expand_shrinker_maps(int new_id)
 		ret = expand_one_shrinker_map(memcg, size, old_size);
 		if (ret) {
 			mem_cgroup_iter_break(NULL, memcg);
-			goto unlock;
+			goto out;
 		}
 	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
-unlock:
+out:
 	if (!ret)
 		memcg_shrinker_map_size = size;
-	mutex_unlock(&memcg_shrinker_map_mutex);
+
 	return ret;
 }
 
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 04/13] mm: vmscan: remove memcg_shrinker_map_size
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (2 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 03/13] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 05/13] mm: vmscan: use kvfree_rcu instead of call_rcu Yang Shi
                   ` (8 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but actually the
map size can be calculated via shrinker_nr_max, so it seems unnecessary to keep both.
Remove memcg_shrinker_map_size since shrinker_nr_max is also used by iterating the
bit map.

Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b08c8d9055ae..641a0b8b4ea9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -185,8 +185,12 @@ static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
 #ifdef CONFIG_MEMCG
+static int shrinker_nr_max;
 
-static int memcg_shrinker_map_size;
+static inline int shrinker_map_size(int nr_items)
+{
+	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
+}
 
 static void free_shrinker_map_rcu(struct rcu_head *head)
 {
@@ -248,7 +252,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
 		return 0;
 
 	down_write(&shrinker_rwsem);
-	size = memcg_shrinker_map_size;
+	size = shrinker_map_size(shrinker_nr_max);
 	for_each_node(nid) {
 		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
 		if (!map) {
@@ -266,12 +270,13 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
 static int expand_shrinker_maps(int new_id)
 {
 	int size, old_size, ret = 0;
+	int new_nr_max = new_id + 1;
 	struct mem_cgroup *memcg;
 
-	size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
-	old_size = memcg_shrinker_map_size;
+	size = shrinker_map_size(new_nr_max);
+	old_size = shrinker_map_size(shrinker_nr_max);
 	if (size <= old_size)
-		return 0;
+		goto out;
 
 	if (!root_mem_cgroup)
 		goto out;
@@ -290,7 +295,7 @@ static int expand_shrinker_maps(int new_id)
 	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 out:
 	if (!ret)
-		memcg_shrinker_map_size = size;
+		shrinker_nr_max = new_nr_max;
 
 	return ret;
 }
@@ -323,7 +328,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
 
 static DEFINE_IDR(shrinker_idr);
-static int shrinker_nr_max;
 
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
@@ -340,8 +344,6 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 			idr_remove(&shrinker_idr, id);
 			goto unlock;
 		}
-
-		shrinker_nr_max = id + 1;
 	}
 	shrinker->id = id;
 	ret = 0;
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 05/13] mm: vmscan: use kvfree_rcu instead of call_rcu
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (3 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 04/13] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 06/13] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
                   ` (7 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Using kvfree_rcu() to free the old shrinker_maps instead of call_rcu().
We don't have to define a dedicated callback for call_rcu() anymore.

Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 641a0b8b4ea9..bbe13985ae05 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -192,11 +192,6 @@ static inline int shrinker_map_size(int nr_items)
 	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
 }
 
-static void free_shrinker_map_rcu(struct rcu_head *head)
-{
-	kvfree(container_of(head, struct memcg_shrinker_map, rcu));
-}
-
 static int expand_one_shrinker_map(struct mem_cgroup *memcg,
 				   int size, int old_size)
 {
@@ -220,7 +215,7 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg,
 		memset((void *)new->map + old_size, 0, size - old_size);
 
 		rcu_assign_pointer(pn->shrinker_map, new);
-		call_rcu(&old->rcu, free_shrinker_map_rcu);
+		kvfree_rcu(old, rcu);
 	}
 
 	return 0;
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 06/13] mm: memcontrol: rename shrinker_map to shrinker_info
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (4 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 05/13] mm: vmscan: use kvfree_rcu instead of call_rcu Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 07/13] mm: vmscan: add shrinker_info_protected() helper Yang Shi
                   ` (6 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

The following patch is going to add nr_deferred into shrinker_map, the change will
make shrinker_map not only include map anymore, so rename it to "memcg_shrinker_info".
And this should make the patch adding nr_deferred cleaner and readable and make
review easier.  Also remove the "memcg_" prefix.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/memcontrol.h |  8 +++---
 mm/memcontrol.c            |  6 ++--
 mm/vmscan.c                | 58 +++++++++++++++++++-------------------
 3 files changed, 36 insertions(+), 36 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index b07dc2d5014d..dc7d0e2cb3ad 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -117,7 +117,7 @@ struct batched_lruvec_stat {
  * Bitmap of shrinker::id corresponding to memcg-aware shrinkers,
  * which have elements charged to this memcg.
  */
-struct memcg_shrinker_map {
+struct shrinker_info {
 	struct rcu_head rcu;
 	unsigned long map[];
 };
@@ -145,7 +145,7 @@ struct mem_cgroup_per_node {
 
 	struct mem_cgroup_reclaim_iter	iter;
 
-	struct memcg_shrinker_map __rcu	*shrinker_map;
+	struct shrinker_info __rcu	*shrinker_info;
 
 	struct rb_node		tree_node;	/* RB tree node */
 	unsigned long		usage_in_excess;/* Set to the value by which */
@@ -1533,8 +1533,8 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
 	return false;
 }
 
-int alloc_shrinker_maps(struct mem_cgroup *memcg);
-void free_shrinker_maps(struct mem_cgroup *memcg);
+int alloc_shrinker_info(struct mem_cgroup *memcg);
+void free_shrinker_info(struct mem_cgroup *memcg);
 void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
 #else
 #define mem_cgroup_sockets_enabled 0
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index aeb1847f159c..35d44afdd9fc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5131,11 +5131,11 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 
 	/*
-	 * A memcg must be visible for expand_shrinker_maps()
+	 * A memcg must be visible for expand_shrinker_info()
 	 * by the time the maps are allocated. So, we allocate maps
 	 * here, when for_each_mem_cgroup() can't skip it.
 	 */
-	if (alloc_shrinker_maps(memcg)) {
+	if (alloc_shrinker_info(memcg)) {
 		mem_cgroup_id_remove(memcg);
 		return -ENOMEM;
 	}
@@ -5199,7 +5199,7 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
 	vmpressure_cleanup(&memcg->vmpressure);
 	cancel_work_sync(&memcg->high_work);
 	mem_cgroup_remove_from_trees(memcg);
-	free_shrinker_maps(memcg);
+	free_shrinker_info(memcg);
 	memcg_free_kmem(memcg);
 	mem_cgroup_free(memcg);
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bbe13985ae05..7fdfdacf9a1f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -192,16 +192,16 @@ static inline int shrinker_map_size(int nr_items)
 	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
 }
 
-static int expand_one_shrinker_map(struct mem_cgroup *memcg,
-				   int size, int old_size)
+static int expand_one_shrinker_info(struct mem_cgroup *memcg,
+				    int size, int old_size)
 {
-	struct memcg_shrinker_map *new, *old;
+	struct shrinker_info *new, *old;
 	struct mem_cgroup_per_node *pn;
 	int nid;
 
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
-		old = rcu_dereference_protected(pn->shrinker_map, true);
+		old = rcu_dereference_protected(pn->shrinker_info, true);
 		/* Not yet online memcg */
 		if (!old)
 			return 0;
@@ -214,17 +214,17 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg,
 		memset(new->map, (int)0xff, old_size);
 		memset((void *)new->map + old_size, 0, size - old_size);
 
-		rcu_assign_pointer(pn->shrinker_map, new);
+		rcu_assign_pointer(pn->shrinker_info, new);
 		kvfree_rcu(old, rcu);
 	}
 
 	return 0;
 }
 
-void free_shrinker_maps(struct mem_cgroup *memcg)
+void free_shrinker_info(struct mem_cgroup *memcg)
 {
 	struct mem_cgroup_per_node *pn;
-	struct memcg_shrinker_map *map;
+	struct shrinker_info *info;
 	int nid;
 
 	if (mem_cgroup_is_root(memcg))
@@ -232,15 +232,15 @@ void free_shrinker_maps(struct mem_cgroup *memcg)
 
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
-		map = rcu_dereference_protected(pn->shrinker_map, true);
-		kvfree(map);
-		rcu_assign_pointer(pn->shrinker_map, NULL);
+		info = rcu_dereference_protected(pn->shrinker_info, true);
+		kvfree(info);
+		rcu_assign_pointer(pn->shrinker_info, NULL);
 	}
 }
 
-int alloc_shrinker_maps(struct mem_cgroup *memcg)
+int alloc_shrinker_info(struct mem_cgroup *memcg)
 {
-	struct memcg_shrinker_map *map;
+	struct shrinker_info *info;
 	int nid, size, ret = 0;
 
 	if (mem_cgroup_is_root(memcg))
@@ -249,20 +249,20 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
 	down_write(&shrinker_rwsem);
 	size = shrinker_map_size(shrinker_nr_max);
 	for_each_node(nid) {
-		map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
-		if (!map) {
-			free_shrinker_maps(memcg);
+		info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid);
+		if (!info) {
+			free_shrinker_info(memcg);
 			ret = -ENOMEM;
 			break;
 		}
-		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map);
+		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
 	}
 	up_write(&shrinker_rwsem);
 
 	return ret;
 }
 
-static int expand_shrinker_maps(int new_id)
+static int expand_shrinker_info(int new_id)
 {
 	int size, old_size, ret = 0;
 	int new_nr_max = new_id + 1;
@@ -282,7 +282,7 @@ static int expand_shrinker_maps(int new_id)
 	do {
 		if (mem_cgroup_is_root(memcg))
 			continue;
-		ret = expand_one_shrinker_map(memcg, size, old_size);
+		ret = expand_one_shrinker_info(memcg, size, old_size);
 		if (ret) {
 			mem_cgroup_iter_break(NULL, memcg);
 			goto out;
@@ -298,13 +298,13 @@ static int expand_shrinker_maps(int new_id)
 void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 {
 	if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
-		struct memcg_shrinker_map *map;
+		struct shrinker_info *info;
 
 		rcu_read_lock();
-		map = rcu_dereference(memcg->nodeinfo[nid]->shrinker_map);
+		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
 		/* Pairs with smp mb in shrink_slab() */
 		smp_mb__before_atomic();
-		set_bit(shrinker_id, map->map);
+		set_bit(shrinker_id, info->map);
 		rcu_read_unlock();
 	}
 }
@@ -335,7 +335,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 		goto unlock;
 
 	if (id >= shrinker_nr_max) {
-		if (expand_shrinker_maps(id)) {
+		if (expand_shrinker_info(id)) {
 			idr_remove(&shrinker_idr, id);
 			goto unlock;
 		}
@@ -665,7 +665,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			struct mem_cgroup *memcg, int priority)
 {
-	struct memcg_shrinker_map *map;
+	struct shrinker_info *info;
 	unsigned long ret, freed = 0;
 	int i;
 
@@ -675,12 +675,12 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 	if (!down_read_trylock(&shrinker_rwsem))
 		return 0;
 
-	map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,
-					true);
-	if (unlikely(!map))
+	info = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
+					 true);
+	if (unlikely(!info))
 		goto unlock;
 
-	for_each_set_bit(i, map->map, shrinker_nr_max) {
+	for_each_set_bit(i, info->map, shrinker_nr_max) {
 		struct shrink_control sc = {
 			.gfp_mask = gfp_mask,
 			.nid = nid,
@@ -691,7 +691,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 		shrinker = idr_find(&shrinker_idr, i);
 		if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
 			if (!shrinker)
-				clear_bit(i, map->map);
+				clear_bit(i, info->map);
 			continue;
 		}
 
@@ -702,7 +702,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 
 		ret = do_shrink_slab(&sc, shrinker, priority);
 		if (ret == SHRINK_EMPTY) {
-			clear_bit(i, map->map);
+			clear_bit(i, info->map);
 			/*
 			 * After the shrinker reported that it had no objects to
 			 * free, but before we cleared the corresponding bit in
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 07/13] mm: vmscan: add shrinker_info_protected() helper
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (5 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 06/13] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 08/13] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
                   ` (5 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

The shrinker_info is dereferenced in a couple of places via rcu_dereference_protected
with different calling conventions, for example, using mem_cgroup_nodeinfo helper
or dereferencing memcg->nodeinfo[nid]->shrinker_info.  And the later patch
will add more dereference places.

So extract the dereference into a helper to make the code more readable.  No
functional change.

Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7fdfdacf9a1f..ef9f1531a6ee 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -192,6 +192,13 @@ static inline int shrinker_map_size(int nr_items)
 	return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
 }
 
+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 size, int old_size)
 {
@@ -201,7 +208,7 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
 
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
-		old = rcu_dereference_protected(pn->shrinker_info, true);
+		old = shrinker_info_protected(memcg, nid);
 		/* Not yet online memcg */
 		if (!old)
 			return 0;
@@ -232,7 +239,7 @@ void free_shrinker_info(struct mem_cgroup *memcg)
 
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
-		info = rcu_dereference_protected(pn->shrinker_info, true);
+		info = shrinker_info_protected(memcg, nid);
 		kvfree(info);
 		rcu_assign_pointer(pn->shrinker_info, NULL);
 	}
@@ -675,8 +682,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 	if (!down_read_trylock(&shrinker_rwsem))
 		return 0;
 
-	info = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
-					 true);
+	info = shrinker_info_protected(memcg, nid);
 	if (unlikely(!info))
 		goto unlock;
 
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 08/13] mm: vmscan: use a new flag to indicate shrinker is registered
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (6 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 07/13] mm: vmscan: add shrinker_info_protected() helper Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 09/13] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
                   ` (4 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
This approach is fine with nr_deferred at the shrinker level, but the following
patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
shrinker->nr_deferred would always be NULL.  This would prevent the shrinkers
from unregistering correctly.

Remove SHRINKER_REGISTERING since we could check if shrinker is registered
successfully by the new flag.

Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/shrinker.h |  7 ++++---
 mm/vmscan.c              | 40 +++++++++++++++-------------------------
 2 files changed, 19 insertions(+), 28 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 0f80123650e2..1eac79ce57d4 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -79,13 +79,14 @@ struct shrinker {
 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
 
 /* Flags */
-#define SHRINKER_NUMA_AWARE	(1 << 0)
-#define SHRINKER_MEMCG_AWARE	(1 << 1)
+#define SHRINKER_REGISTERED	(1 << 0)
+#define SHRINKER_NUMA_AWARE	(1 << 1)
+#define SHRINKER_MEMCG_AWARE	(1 << 2)
 /*
  * 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 << 2)
+#define SHRINKER_NONSLAB	(1 << 3)
 
 extern int prealloc_shrinker(struct shrinker *shrinker);
 extern void register_shrinker_prepared(struct shrinker *shrinker);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ef9f1531a6ee..34cf3d84309c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -316,19 +316,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 	}
 }
 
-/*
- * We allow subsystems to populate their shrinker-related
- * LRU lists before register_shrinker_prepared() is called
- * for the shrinker, since we don't want to impose
- * restrictions on their internal registration order.
- * In this case shrink_slab_memcg() may find corresponding
- * bit is set in the shrinkers map.
- *
- * This value is used by the function to detect registering
- * shrinkers and to skip do_shrink_slab() calls for them.
- */
-#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
-
 static DEFINE_IDR(shrinker_idr);
 
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
@@ -337,7 +324,7 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 
 	down_write(&shrinker_rwsem);
 	/* This may call shrinker, so it must use down_read_trylock() */
-	id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
+	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
 	if (id < 0)
 		goto unlock;
 
@@ -360,9 +347,9 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
 
 	BUG_ON(id < 0);
 
-	down_write(&shrinker_rwsem);
+	lockdep_assert_held(&shrinker_rwsem);
+
 	idr_remove(&shrinker_idr, id);
-	up_write(&shrinker_rwsem);
 }
 
 static bool cgroup_reclaim(struct scan_control *sc)
@@ -490,8 +477,11 @@ void free_prealloced_shrinker(struct shrinker *shrinker)
 	if (!shrinker->nr_deferred)
 		return;
 
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+	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;
@@ -501,10 +491,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
 {
 	down_write(&shrinker_rwsem);
 	list_add_tail(&shrinker->list, &shrinker_list);
-#ifdef CONFIG_MEMCG
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		idr_replace(&shrinker_idr, shrinker, shrinker->id);
-#endif
+	shrinker->flags |= SHRINKER_REGISTERED;
 	up_write(&shrinker_rwsem);
 }
 
@@ -524,13 +511,16 @@ EXPORT_SYMBOL(register_shrinker);
  */
 void unregister_shrinker(struct shrinker *shrinker)
 {
-	if (!shrinker->nr_deferred)
+	if (!(shrinker->flags & SHRINKER_REGISTERED))
 		return;
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
-		unregister_memcg_shrinker(shrinker);
+
 	down_write(&shrinker_rwsem);
 	list_del(&shrinker->list);
+	shrinker->flags &= ~SHRINKER_REGISTERED;
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
 	up_write(&shrinker_rwsem);
+
 	kfree(shrinker->nr_deferred);
 	shrinker->nr_deferred = NULL;
 }
@@ -695,7 +685,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 		struct shrinker *shrinker;
 
 		shrinker = idr_find(&shrinker_idr, i);
-		if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
+		if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
 			if (!shrinker)
 				clear_bit(i, info->map);
 			continue;
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 09/13] mm: vmscan: add per memcg shrinker nr_deferred
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (7 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 08/13] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 10/13] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
                   ` (3 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Currently the number of deferred objects are per shrinker, but some slabs, for
example, vfs inode/dentry cache are per memcg, this would result in poor
isolation among memcgs.

The deferred objects typically are generated by __GFP_NOFS allocations, one
memcg with excessive __GFP_NOFS allocations may blow up deferred objects, then
other innocent memcgs may suffer from over shrink, excessive reclaim latency,
etc.

For example, two workloads run in memcgA and memcgB respectively, workload in
B is vfs heavy workload.  Workload in A generates excessive deferred objects,
then B's vfs cache might be hit heavily (drop half of caches) by B's limit
reclaim or global reclaim.

We observed this hit in our production environment which was running vfs heavy
workload shown as the below tracing log:

<...>-409454 [016] .... 28286961.747146: mm_shrink_slab_start: super_cache_scan+0x0/0x1a0 ffff9a83046f3458:
nid: 1 objects to shrink 3641681686040 gfp_flags GFP_HIGHUSER_MOVABLE|__GFP_ZERO pgs_scanned 1 lru_pgs 15721
cache items 246404277 delta 31345 total_scan 123202138
<...>-409454 [022] .... 28287105.928018: mm_shrink_slab_end: super_cache_scan+0x0/0x1a0 ffff9a83046f3458:
nid: 1 unused scan count 3641681686040 new scan count 3641798379189 total_scan 602
last shrinker return val 123186855

The vfs cache and page cache ratio was 10:1 on this machine, and half of caches
were dropped.  This also resulted in significant amount of page caches were
dropped due to inodes eviction.

Make nr_deferred per memcg for memcg aware shrinkers would solve the unfairness
and bring better isolation.

The following patch will add nr_deferred to parent memcg when memcg offline.
To preserve nr_deferred when reparenting memcgs to root, root memcg needs
shrinker_info allocated too.

When memcg is not enabled (!CONFIG_MEMCG or memcg disabled), the shrinker's
nr_deferred would be used.  And non memcg aware shrinkers use shrinker's
nr_deferred all the time.

Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/memcontrol.h |  7 +++--
 mm/vmscan.c                | 60 ++++++++++++++++++++++++++------------
 2 files changed, 46 insertions(+), 21 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index dc7d0e2cb3ad..24e735434a46 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -114,12 +114,13 @@ struct batched_lruvec_stat {
 };
 
 /*
- * Bitmap of shrinker::id corresponding to memcg-aware shrinkers,
- * which have elements charged to this memcg.
+ * 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;
-	unsigned long map[];
+	atomic_long_t *nr_deferred;
+	unsigned long *map;
 };
 
 /*
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 34cf3d84309c..397f3b67bad8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -187,11 +187,17 @@ static 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)
 {
@@ -200,11 +206,13 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
 }
 
 static int expand_one_shrinker_info(struct mem_cgroup *memcg,
-				    int size, int old_size)
+				    int map_size, int defer_size,
+				    int old_map_size, int old_defer_size)
 {
 	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];
@@ -217,9 +225,16 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
 		if (!new)
 			return -ENOMEM;
 
-		/* Set all old bits, clear all new bits */
-		memset(new->map, (int)0xff, old_size);
-		memset((void *)new->map + old_size, 0, size - old_size);
+		new->nr_deferred = (atomic_long_t *)(new + 1);
+		new->map = (void *)new->nr_deferred + defer_size;
+
+		/* 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);
@@ -234,9 +249,6 @@ void free_shrinker_info(struct mem_cgroup *memcg)
 	struct shrinker_info *info;
 	int nid;
 
-	if (mem_cgroup_is_root(memcg))
-		return;
-
 	for_each_node(nid) {
 		pn = memcg->nodeinfo[nid];
 		info = shrinker_info_protected(memcg, nid);
@@ -249,12 +261,12 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 {
 	struct shrinker_info *info;
 	int nid, size, ret = 0;
-
-	if (mem_cgroup_is_root(memcg))
-		return 0;
+	int map_size, defer_size = 0;
 
 	down_write(&shrinker_rwsem);
-	size = shrinker_map_size(shrinker_nr_max);
+	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) {
@@ -262,6 +274,8 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 			ret = -ENOMEM;
 			break;
 		}
+		info->nr_deferred = (atomic_long_t *)(info + 1);
+		info->map = (void *)info->nr_deferred + defer_size;
 		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
 	}
 	up_write(&shrinker_rwsem);
@@ -269,15 +283,21 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 	return ret;
 }
 
+static inline bool need_expand(int nr_max)
+{
+	return round_up(nr_max, BITS_PER_LONG) >
+	       round_up(shrinker_nr_max, BITS_PER_LONG);
+}
+
 static int expand_shrinker_info(int new_id)
 {
-	int size, old_size, ret = 0;
+	int ret = 0;
 	int new_nr_max = new_id + 1;
+	int map_size, defer_size = 0;
+	int old_map_size, old_defer_size = 0;
 	struct mem_cgroup *memcg;
 
-	size = shrinker_map_size(new_nr_max);
-	old_size = shrinker_map_size(shrinker_nr_max);
-	if (size <= old_size)
+	if (!need_expand(new_nr_max))
 		goto out;
 
 	if (!root_mem_cgroup)
@@ -285,11 +305,15 @@ 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);
+
 	memcg = mem_cgroup_iter(NULL, NULL, NULL);
 	do {
-		if (mem_cgroup_is_root(memcg))
-			continue;
-		ret = expand_one_shrinker_info(memcg, size, old_size);
+		ret = expand_one_shrinker_info(memcg, map_size, defer_size,
+					       old_map_size, old_defer_size);
 		if (ret) {
 			mem_cgroup_iter_break(NULL, memcg);
 			goto out;
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 10/13] mm: vmscan: use per memcg nr_deferred of shrinker
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (8 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 09/13] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 11/13] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
                   ` (2 subsequent siblings)
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Use per memcg's nr_deferred for memcg aware shrinkers.  The shrinker's nr_deferred
will be used in the following cases:
    1. Non memcg aware shrinkers
    2. !CONFIG_MEMCG
    3. memcg is disabled by boot parameter

Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 78 ++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 66 insertions(+), 12 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 397f3b67bad8..5bc6975cb635 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -376,6 +376,24 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
 	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]);
+}
+
 static bool cgroup_reclaim(struct scan_control *sc)
 {
 	return sc->target_mem_cgroup;
@@ -414,6 +432,18 @@ 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;
@@ -425,6 +455,39 @@ static bool writeback_throttling_sane(struct scan_control *sc)
 }
 #endif
 
+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]);
+}
+
 /*
  * This misses isolated pages which are not accounted for to save counters.
  * As the data only determines if reclaim or compaction continues, it is
@@ -561,14 +624,10 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	long freeable;
 	long nr;
 	long new_nr;
-	int nid = shrinkctl->nid;
 	long batch_size = shrinker->batch ? shrinker->batch
 					  : SHRINK_BATCH;
 	long scanned = 0, next_deferred;
 
-	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
-		nid = 0;
-
 	freeable = shrinker->count_objects(shrinker, shrinkctl);
 	if (freeable == 0 || freeable == SHRINK_EMPTY)
 		return freeable;
@@ -578,7 +637,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	 * and zero it so that other concurrent shrinker invocations
 	 * don't also do this scanning work.
 	 */
-	nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
+	nr = xchg_nr_deferred(shrinker, shrinkctl);
 
 	total_scan = nr;
 	if (shrinker->seeks) {
@@ -669,14 +728,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 		next_deferred = 0;
 	/*
 	 * move the unused scan count back into the shrinker in a
-	 * manner that handles concurrent updates. If we exhausted the
-	 * scan, there is no need to do an update.
+	 * manner that handles concurrent updates.
 	 */
-	if (next_deferred > 0)
-		new_nr = atomic_long_add_return(next_deferred,
-						&shrinker->nr_deferred[nid]);
-	else
-		new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
+	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;
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 11/13] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (9 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 10/13] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 12/13] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 13/13] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Now nr_deferred is available on per memcg level for memcg aware shrinkers, so don't need
allocate shrinker->nr_deferred for such shrinkers anymore.

The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or memcg is disabled
by kernel command line, then shrinker's SHRINKER_MEMCG_AWARE flag would be cleared.
This makes the implementation of this patch simpler.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5bc6975cb635..324c34c6e5cf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -346,6 +346,9 @@ 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);
@@ -425,7 +428,7 @@ static bool writeback_throttling_sane(struct scan_control *sc)
 #else
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
-	return 0;
+	return -ENOSYS;
 }
 
 static void unregister_memcg_shrinker(struct shrinker *shrinker)
@@ -537,8 +540,18 @@ static unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru,
  */
 int prealloc_shrinker(struct shrinker *shrinker)
 {
-	unsigned int size = sizeof(*shrinker->nr_deferred);
+	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;
 
@@ -546,28 +559,16 @@ int prealloc_shrinker(struct shrinker *shrinker)
 	if (!shrinker->nr_deferred)
 		return -ENOMEM;
 
-	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
-		if (prealloc_memcg_shrinker(shrinker))
-			goto free_deferred;
-	}
-
 	return 0;
-
-free_deferred:
-	kfree(shrinker->nr_deferred);
-	shrinker->nr_deferred = NULL;
-	return -ENOMEM;
 }
 
 void free_prealloced_shrinker(struct shrinker *shrinker)
 {
-	if (!shrinker->nr_deferred)
-		return;
-
 	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
 		down_write(&shrinker_rwsem);
 		unregister_memcg_shrinker(shrinker);
 		up_write(&shrinker_rwsem);
+		return;
 	}
 
 	kfree(shrinker->nr_deferred);
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 12/13] mm: memcontrol: reparent nr_deferred when memcg offline
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (10 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 11/13] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  2021-03-11 19:08 ` [v10 PATCH 13/13] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

Now shrinker's nr_deferred is per memcg for memcg aware shrinkers, add to parent's
corresponding nr_deferred when memcg offline.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 include/linux/memcontrol.h |  1 +
 mm/memcontrol.c            |  1 +
 mm/vmscan.c                | 24 ++++++++++++++++++++++++
 3 files changed, 26 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 24e735434a46..4064c9dda534 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1537,6 +1537,7 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
 int alloc_shrinker_info(struct mem_cgroup *memcg);
 void free_shrinker_info(struct mem_cgroup *memcg);
 void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
+void reparent_shrinker_deferred(struct mem_cgroup *memcg);
 #else
 #define mem_cgroup_sockets_enabled 0
 static inline void mem_cgroup_sk_alloc(struct sock *sk) { };
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 35d44afdd9fc..a945dfc85156 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5167,6 +5167,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 	page_counter_set_low(&memcg->memory, 0);
 
 	memcg_offline_kmem(memcg);
+	reparent_shrinker_deferred(memcg);
 	wb_memcg_offline(memcg);
 
 	drain_all_stock(memcg);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 324c34c6e5cf..d0791ebd6761 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -397,6 +397,30 @@ static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
 	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 < shrinker_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);
+}
+
 static bool cgroup_reclaim(struct scan_control *sc)
 {
 	return sc->target_mem_cgroup;
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

* [v10 PATCH 13/13] mm: vmscan: shrink deferred objects proportional to priority
  2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
                   ` (11 preceding siblings ...)
  2021-03-11 19:08 ` [v10 PATCH 12/13] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
@ 2021-03-11 19:08 ` Yang Shi
  12 siblings, 0 replies; 14+ messages in thread
From: Yang Shi @ 2021-03-11 19:08 UTC (permalink / raw)
  To: guro, ktkhai, vbabka, shakeelb, david, hannes, mhocko, akpm
  Cc: shy828301, linux-mm, linux-fsdevel, linux-kernel

The number of deferred objects might get windup to an absurd number, and it
results in clamp of slab objects.  It is undesirable for sustaining workingset.

So shrink deferred objects proportional to priority and cap nr_deferred to twice
of cache items.

The idea is borrowed from Dave Chinner's patch:
https://lore.kernel.org/linux-xfs/20191031234618.15403-13-david@fromorbit.com/

Tested with kernel build and vfs metadata heavy workload in our production
environment, no regression is spotted so far.

Signed-off-by: Yang Shi <shy828301@gmail.com>
---
 mm/vmscan.c | 46 +++++++++++-----------------------------------
 1 file changed, 11 insertions(+), 35 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d0791ebd6761..163616e78a4e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -664,7 +664,6 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	 */
 	nr = xchg_nr_deferred(shrinker, shrinkctl);
 
-	total_scan = nr;
 	if (shrinker->seeks) {
 		delta = freeable >> priority;
 		delta *= 4;
@@ -678,37 +677,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 		delta = freeable / 2;
 	}
 
+	total_scan = nr >> priority;
 	total_scan += delta;
-	if (total_scan < 0) {
-		pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n",
-		       shrinker->scan_objects, total_scan);
-		total_scan = freeable;
-		next_deferred = nr;
-	} else
-		next_deferred = total_scan;
-
-	/*
-	 * We need to avoid excessive windup on filesystem shrinkers
-	 * due to large numbers of GFP_NOFS allocations causing the
-	 * shrinkers to return -1 all the time. This results in a large
-	 * nr being built up so when a shrink that can do some work
-	 * comes along it empties the entire cache due to nr >>>
-	 * freeable. This is bad for sustaining a working set in
-	 * memory.
-	 *
-	 * Hence only allow the shrinker to scan the entire cache when
-	 * a large delta change is calculated directly.
-	 */
-	if (delta < freeable / 4)
-		total_scan = min(total_scan, freeable / 2);
-
-	/*
-	 * Avoid risking looping forever due to too large nr value:
-	 * never try to free more than twice the estimate number of
-	 * freeable entries.
-	 */
-	if (total_scan > freeable * 2)
-		total_scan = freeable * 2;
+	total_scan = min(total_scan, (2 * freeable));
 
 	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
 				   freeable, delta, total_scan, priority);
@@ -747,10 +718,15 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 		cond_resched();
 	}
 
-	if (next_deferred >= scanned)
-		next_deferred -= scanned;
-	else
-		next_deferred = 0;
+	/*
+	 * 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.
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 14+ messages in thread

end of thread, other threads:[~2021-03-11 19:10 UTC | newest]

Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-03-11 19:08 [v10 PATCH 00/13] Make shrinker's nr_deferred memcg aware Yang Shi
2021-03-11 19:08 ` [v10 PATCH 01/13] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2021-03-11 19:08 ` [v10 PATCH 02/13] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
2021-03-11 19:08 ` [v10 PATCH 03/13] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
2021-03-11 19:08 ` [v10 PATCH 04/13] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
2021-03-11 19:08 ` [v10 PATCH 05/13] mm: vmscan: use kvfree_rcu instead of call_rcu Yang Shi
2021-03-11 19:08 ` [v10 PATCH 06/13] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
2021-03-11 19:08 ` [v10 PATCH 07/13] mm: vmscan: add shrinker_info_protected() helper Yang Shi
2021-03-11 19:08 ` [v10 PATCH 08/13] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2021-03-11 19:08 ` [v10 PATCH 09/13] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
2021-03-11 19:08 ` [v10 PATCH 10/13] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2021-03-11 19:08 ` [v10 PATCH 11/13] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2021-03-11 19:08 ` [v10 PATCH 12/13] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2021-03-11 19:08 ` [v10 PATCH 13/13] mm: vmscan: shrink deferred objects proportional to priority Yang Shi

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