From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755697AbcBDMSJ (ORCPT ); Thu, 4 Feb 2016 07:18:09 -0500 Received: from mx2.parallels.com ([199.115.105.18]:36114 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755247AbcBDMSG (ORCPT ); Thu, 4 Feb 2016 07:18:06 -0500 From: Vladimir Davydov To: Andrew Morton CC: Johannes Weiner , Michal Hocko , , Subject: [PATCH] mm: memcontrol: do not bypass slab charge if memcg is offline Date: Thu, 4 Feb 2016 15:17:55 +0300 Message-ID: <1454588275-7615-1-git-send-email-vdavydov@virtuozzo.com> X-Mailer: git-send-email 2.1.4 MIME-Version: 1.0 Content-Type: text/plain X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To US-EXCH.sw.swsoft.com (10.255.249.47) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Slab pages are charged in two steps. First, an appropriate per memcg cache is selected (see memcg_kmem_get_cache) basing on the current context, then the new slab page is charged to the memory cgroup which the selected cache was created for (see memcg_charge_slab -> __memcg_kmem_charge_memcg). It is OK to bypass kmemcg charge at step 1, but if step 1 succeeded and we successfully allocated a new slab page, step 2 must be performed, otherwise we would get a per memcg kmem cache which contains a slab that does not hold a reference to the memory cgroup owning the cache. Since per memcg kmem caches are destroyed on memcg css free, this could result in freeing a cache while there are still active objects in it. However, currently we will bypass slab page charge if the memory cgroup owning the cache is offline (see __memcg_kmem_charge_memcg). This is very unlikely to occur in practice, because for this to happen a process must be migrated to a different cgroup and the old cgroup must be removed while the process is in kmalloc somewhere between steps 1 and 2 (e.g. trying to allocate a new page). Nevertheless, it's still better to eliminate such a possibility. Signed-off-by: Vladimir Davydov --- mm/memcontrol.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 3e4199830456..f36b20f5b3ed 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2325,9 +2325,6 @@ int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order, struct page_counter *counter; int ret; - if (!memcg_kmem_online(memcg)) - return 0; - ret = try_charge(memcg, gfp, nr_pages); if (ret) return ret; @@ -2346,10 +2343,11 @@ int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order, int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order) { struct mem_cgroup *memcg; - int ret; + int ret = 0; memcg = get_mem_cgroup_from_mm(current->mm); - ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg); + if (memcg_kmem_online(memcg)) + ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg); css_put(&memcg->css); return ret; } -- 2.1.4