[PATCH 09/10] slab: remove slub sysfs interface files early for empty memcg caches
From: Tejun Heo <tj@kernel.org>
Date: 2017-01-17 23:57:00
Also in:
linux-mm, lkml
Subsystem:
memory management, slab allocator, the rest · Maintainers:
Andrew Morton, Vlastimil Babka, Harry Yoo, Linus Torvalds
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. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Jay Vana <redacted> Acked-by: Vladimir Davydov <redacted> Cc: Christoph Lameter <redacted> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <redacted> Cc: Andrew Morton <akpm@linux-foundation.org> --- mm/slub.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 184f80b..5bffa1f 100644
--- a/mm/slub.c
+++ b/mm/slub.c@@ -3951,8 +3951,20 @@ 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)
@@ -5651,6 +5663,15 @@ 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
--
2.9.3
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