Commit 50862ce7 authored Feb 22, 2017 by Tejun Heo Committed by Linus Torvalds Feb 22, 2017

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@kernel.org


Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jay Vana <jsvana@fb.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 01fb58bc

mm/slub.c

+23 −2

Original line number	Diff line number	Diff line
		@@ -3959,8 +3959,20 @@ int __kmem_cache_shrink(struct kmem_cache *s)
		#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)
		@@ -5659,6 +5671,15 @@ static void sysfs_slab_remove(struct kmem_cache *s)
		*/
		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

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