From 50862ce711b3e9cf8511df7a356892e128b037d3 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 22 Feb 2017 15:41:33 -0800 Subject: [PATCH] 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 Reported-by: Jay Vana Acked-by: Vladimir Davydov Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 62d0b557a596..af38aaad34b0 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -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