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slab: remove synchronous synchronize_sched() from memcg cache deactivation path

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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.

slub uses synchronize_sched() to deactivate a memcg cache.
synchronize_sched() is an expensive and slow operation and doesn't scale
when a huge number of caches are destroyed back-to-back.  While there
used to be a simple batching mechanism, the batching was too restricted
to be helpful.

This patch implements slab_deactivate_memcg_cache_rcu_sched() which slub
can use to schedule sched RCU callback instead of performing
synchronize_sched() synchronously while holding cgroup_mutex.  While
this adds online cpus, mems and slab_mutex operations, operating on
these locks back-to-back from the same kworker, which is what's gonna
happen when there are many to deactivate, isn't expensive at all and
this gets rid of the scalability problem completely.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Tejun Heo <[email protected]>
Reported-by: Jay Vana <[email protected]>
Acked-by: Vladimir Davydov <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Tejun Heo 2017-02-22 15:41:30 -08:00 • committed by Linus Torvalds
commit 01fb58bcba
4 changed files with 76 additions and 4 deletions
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12
mm/slub.c
View file

@ -3957,6 +3957,12 @@ 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);
}
void __kmemcg_cache_deactivate(struct kmem_cache *s)
{
/*
@ -3968,11 +3974,9 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
/*
* s->cpu_partial is checked locklessly (see put_cpu_partial), so
* we have to make sure the change is visible.
* we have to make sure the change is visible before shrinking.
*/
synchronize_sched();
__kmem_cache_shrink(s);
slab_deactivate_memcg_cache_rcu_sched(s, kmemcg_cache_deact_after_rcu);
}
#endif