From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 267376B026B for ; Sat, 14 Jan 2017 00:55:15 -0500 (EST) Received: by mail-pf0-f199.google.com with SMTP id 80so174417522pfy.2 for ; Fri, 13 Jan 2017 21:55:15 -0800 (PST) Received: from mail-pg0-x244.google.com (mail-pg0-x244.google.com. [2607:f8b0:400e:c05::244]) by mx.google.com with ESMTPS id h14si14765157plk.127.2017.01.13.21.55.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 13 Jan 2017 21:55:14 -0800 (PST) Received: by mail-pg0-x244.google.com with SMTP id b1so344431pgc.1 for ; Fri, 13 Jan 2017 21:55:14 -0800 (PST) From: Tejun Heo Subject: [PATCH 9/9] slab: remove slub sysfs interface files early for empty memcg caches Date: Sat, 14 Jan 2017 00:54:49 -0500 Message-Id: <20170114055449.11044-10-tj@kernel.org> In-Reply-To: <20170114055449.11044-1-tj@kernel.org> References: <20170114055449.11044-1-tj@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: vdavydov.dev@gmail.com, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org Cc: jsvana@fb.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, kernel-team@fb.com, Tejun Heo 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 Reported-by: Jay Vana Cc: Vladimir Davydov Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andrew Morton --- mm/slub.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 8621940..41a3da7 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) @@ -5650,6 +5662,15 @@ 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org