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>
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mm/slub.c
25
mm/slub.c
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@ -3959,8 +3959,20 @@ int __kmem_cache_shrink(struct kmem_cache *s)
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#ifdef CONFIG_MEMCG
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static void kmemcg_cache_deact_after_rcu(struct kmem_cache *s)
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{
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/* called with all the locks held after a sched RCU grace period */
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__kmem_cache_shrink(s);
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/*
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* Called with all the locks held after a sched RCU grace period.
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* Even if @s becomes empty after shrinking, we can't know that @s
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* doesn't have allocations already in-flight and thus can't
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* destroy @s until the associated memcg is released.
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*
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* However, let's remove the sysfs files for empty caches here.
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* Each cache has a lot of interface files which aren't
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* particularly useful for empty draining caches; otherwise, we can
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* easily end up with millions of unnecessary sysfs files on
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* systems which have a lot of memory and transient cgroups.
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*/
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if (!__kmem_cache_shrink(s))
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sysfs_slab_remove(s);
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}
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void __kmemcg_cache_deactivate(struct kmem_cache *s)
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@ -5659,6 +5671,15 @@ static void sysfs_slab_remove(struct kmem_cache *s)
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*/
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return;
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if (!s->kobj.state_in_sysfs)
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/*
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* For a memcg cache, this may be called during
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* deactivation and again on shutdown. Remove only once.
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* A cache is never shut down before deactivation is
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* complete, so no need to worry about synchronization.
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*/
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return;
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#ifdef CONFIG_MEMCG
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kset_unregister(s->memcg_kset);
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#endif
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