The patch titled
Subject: slab: remove slub sysfs interface files early for empty memcg caches
has been added to the -mm tree. Its filename is
slab-remove-slub-sysfs-interface-files-early-for-empty-memcg-caches.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/slab-remove-slub-sysfs-interface-files-early-for-empty-memcg-caches.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/slab-remove-slub-sysfs-interface-files-early-for-empty-memcg-caches.patch
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------------------------------------------------------
From: Tejun Heo <tj@xxxxxxxxxx>
Subject: slab: remove slub sysfs interface files early for empty memcg caches
With kmem cgroup support enabled, kmem_caches can be created and destroyed
frequently and a great number of near empty kmem_caches can accumulate if
there are a lot of transient cgroups and the system is not under memory
pressure. When memory reclaim starts under such conditions, it can lead
to consecutive deactivation and destruction of many kmem_caches, easily
hundreds of thousands on moderately large systems, exposing scalability
issues in the current slab management code. This is one of the patches to
address the issue.
Each cache has a number of sysfs interface files under /sys/kernel/slab.
On a system with a lot of memory and transient memcgs, the number of
interface files which have to be removed once memory reclaim kicks in can
reach millions.
Link: http://lkml.kernel.org/r/20170117235411.9408-10-tj@xxxxxxxxxx
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Jay Vana <jsvana@xxxxxx>
Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slub.c | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)
diff -puN mm/slub.c~slab-remove-slub-sysfs-interface-files-early-for-empty-memcg-caches mm/slub.c
--- a/mm/slub.c~slab-remove-slub-sysfs-interface-files-early-for-empty-memcg-caches
+++ a/mm/slub.c
@@ -3955,8 +3955,20 @@ int __kmem_cache_shrink(struct kmem_cach
#ifdef CONFIG_MEMCG
static void kmemcg_cache_deact_after_rcu(struct kmem_cache *s)
{
- /* called with all the locks held after a sched RCU grace period */
- __kmem_cache_shrink(s);
+ /*
+ * Called with all the locks held after a sched RCU grace period.
+ * Even if @s becomes empty after shrinking, we can't know that @s
+ * doesn't have allocations already in-flight and thus can't
+ * destroy @s until the associated memcg is released.
+ *
+ * However, let's remove the sysfs files for empty caches here.
+ * Each cache has a lot of interface files which aren't
+ * particularly useful for empty draining caches; otherwise, we can
+ * easily end up with millions of unnecessary sysfs files on
+ * systems which have a lot of memory and transient cgroups.
+ */
+ if (!__kmem_cache_shrink(s))
+ sysfs_slab_remove(s);
}
void __kmemcg_cache_deactivate(struct kmem_cache *s)
@@ -5655,6 +5667,15 @@ static void sysfs_slab_remove(struct kme
*/
return;
+ if (!s->kobj.state_in_sysfs)
+ /*
+ * For a memcg cache, this may be called during
+ * deactivation and again on shutdown. Remove only once.
+ * A cache is never shut down before deactivation is
+ * complete, so no need to worry about synchronization.
+ */
+ return;
+
#ifdef CONFIG_MEMCG
kset_unregister(s->memcg_kset);
#endif
_
Patches currently in -mm which might be from tj@xxxxxxxxxx are
revert-slub-move-synchronize_sched-out-of-slab_mutex-on-shrink.patch
slub-separate-out-sysfs_slab_release-from-sysfs_slab_remove.patch
slab-remove-synchronous-rcu_barrier-call-in-memcg-cache-release-path.patch
slab-reorganize-memcg_cache_params.patch
slab-link-memcg-kmem_caches-on-their-associated-memory-cgroup.patch
slab-implement-slab_root_caches-list.patch
slab-introduce-__kmemcg_cache_deactivate.patch
slab-remove-synchronous-synchronize_sched-from-memcg-cache-deactivation-path.patch
slab-remove-slub-sysfs-interface-files-early-for-empty-memcg-caches.patch
slab-use-memcg_kmem_cache_wq-for-slab-destruction-operations.patch
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