From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f171.google.com (mail-lb0-f171.google.com [209.85.217.171]) by kanga.kvack.org (Postfix) with ESMTP id 8007C6B003A for ; Wed, 18 Dec 2013 08:17:10 -0500 (EST) Received: by mail-lb0-f171.google.com with SMTP id w7so2101128lbi.30 for ; Wed, 18 Dec 2013 05:17:09 -0800 (PST) Received: from relay.parallels.com (relay.parallels.com. [195.214.232.42]) by mx.google.com with ESMTPS id rc10si2874933lbb.164.2013.12.18.05.17.08 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 18 Dec 2013 05:17:09 -0800 (PST) From: Vladimir Davydov Subject: [PATCH 3/6] memcg, slab: cleanup barrier usage when accessing memcg_caches Date: Wed, 18 Dec 2013 17:16:54 +0400 Message-ID: In-Reply-To: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, devel@openvz.org, Johannes Weiner , Glauber Costa , Christoph Lameter , Pekka Enberg , Andrew Morton First, in memcg_create_kmem_cache() we should issue the write barrier after the kmem_cache is initialized, but before storing the pointer to it in its parent's memcg_params. Second, we should always issue the read barrier after cache_from_memcg_idx() to conform with the write barrier. Third, its better to use smp_* versions of barriers, because we don't need them on UP systems. Signed-off-by: Vladimir Davydov Cc: Michal Hocko Cc: Johannes Weiner Cc: Glauber Costa Cc: Christoph Lameter Cc: Pekka Enberg Cc: Andrew Morton --- mm/memcontrol.c | 24 ++++++++++-------------- mm/slab.h | 6 +++++- 2 files changed, 15 insertions(+), 15 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e6ad6ff..e37fdb5 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3429,12 +3429,14 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg, atomic_set(&new_cachep->memcg_params->nr_pages , 0); - cachep->memcg_params->memcg_caches[idx] = new_cachep; /* - * the readers won't lock, make sure everybody sees the updated value, - * so they won't put stuff in the queue again for no reason + * Since readers won't lock (see cache_from_memcg_idx()), we need a + * barrier here to ensure nobody will see the kmem_cache partially + * initialized. */ - wmb(); + smp_wmb(); + + cachep->memcg_params->memcg_caches[idx] = new_cachep; out: mutex_unlock(&memcg_cache_mutex); return new_cachep; @@ -3573,7 +3575,7 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp) { struct mem_cgroup *memcg; - int idx; + struct kmem_cache *memcg_cachep; VM_BUG_ON(!cachep->memcg_params); VM_BUG_ON(!cachep->memcg_params->is_root_cache); @@ -3587,15 +3589,9 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep, if (!memcg_can_account_kmem(memcg)) goto out; - idx = memcg_cache_id(memcg); - - /* - * barrier to mare sure we're always seeing the up to date value. The - * code updating memcg_caches will issue a write barrier to match this. - */ - read_barrier_depends(); - if (likely(cache_from_memcg_idx(cachep, idx))) { - cachep = cache_from_memcg_idx(cachep, idx); + memcg_cachep = cache_from_memcg_idx(cachep, memcg_cache_id(memcg)); + if (likely(memcg_cachep)) { + cachep = memcg_cachep; goto out; } diff --git a/mm/slab.h b/mm/slab.h index 0859c42..1d8b53f 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -163,9 +163,13 @@ static inline const char *cache_name(struct kmem_cache *s) static inline struct kmem_cache * cache_from_memcg_idx(struct kmem_cache *s, int idx) { + struct kmem_cache *cachep; + if (!s->memcg_params) return NULL; - return s->memcg_params->memcg_caches[idx]; + cachep = s->memcg_params->memcg_caches[idx]; + smp_read_barrier_depends(); /* see memcg_register_cache() */ + return cachep; } static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s) -- 1.7.10.4 -- 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