From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756172Ab3LDXwU (ORCPT ); Wed, 4 Dec 2013 18:52:20 -0500 Received: from mail-yh0-f44.google.com ([209.85.213.44]:43981 "EHLO mail-yh0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756141Ab3LDXwA (ORCPT ); Wed, 4 Dec 2013 18:52:00 -0500 Date: Wed, 4 Dec 2013 15:51:57 -0800 (PST) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Johannes Weiner cc: Andrew Morton , Michal Hocko , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 2/2] mm: memcg: do not allow task about to OOM kill to bypass the limit In-Reply-To: <1386197114-5317-3-git-send-email-hannes@cmpxchg.org> Message-ID: References: <1386197114-5317-1-git-send-email-hannes@cmpxchg.org> <1386197114-5317-3-git-send-email-hannes@cmpxchg.org> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 4 Dec 2013, Johannes Weiner wrote: > 4942642080ea ("mm: memcg: handle non-error OOM situations more > gracefully") allowed tasks that already entered a memcg OOM condition > to bypass the memcg limit on subsequent allocation attempts hoping > this would expedite finishing the page fault and executing the kill. > > David Rientjes is worried that this breaks memcg isolation guarantees > and since there is no evidence that the bypass actually speeds up > fault processing just change it so that these subsequent charge > attempts fail outright. The notable exception being __GFP_NOFAIL > charges which are required to bypass the limit regardless. > > Reported-by: David Rientjes > Signed-off-by: Johannes Weiner Acked-by: David Rientjes Thanks! I think we should consider marking this for stable@vger.kernel.org for 3.12 since the original patch went into 3.12-rc6. Depending on the number of allocators in the oom memcg, the amount of memory bypassed can become quite large. For example, in a memcg with a limit of 128MB, if you start 10 concurrent processes that simply allocate a lot of memory you can get quite a bit of memory bypassed. If I start 10 membench processes, which would cause a 128MB memcg to oom even if only one such process were running, we get: # grep RSS /proc/1092[0-9]/status VmRSS: 15724 kB VmRSS: 15064 kB VmRSS: 13224 kB VmRSS: 14520 kB VmRSS: 14472 kB VmRSS: 13016 kB VmRSS: 13024 kB VmRSS: 14560 kB VmRSS: 14864 kB VmRSS: 14772 kB And all of those total ~140MB of memory while bound to a memcg with a 128MB limit, about 10% of memory is bypassed.