From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx204.postini.com [74.125.245.204]) by kanga.kvack.org (Postfix) with SMTP id 990B96B0044 for ; Wed, 7 Nov 2012 17:10:27 -0500 (EST) Date: Wed, 7 Nov 2012 14:10:25 -0800 From: Andrew Morton Subject: Re: [PATCH v2] memcg: oom: fix totalpages calculation for memory.swappiness==0 Message-Id: <20121107141025.2ac62206.akpm@linux-foundation.org> In-Reply-To: <20121015220354.GA11682@dhcp22.suse.cz> References: <20121011085038.GA29295@dhcp22.suse.cz> <1349945859-1350-1-git-send-email-mhocko@suse.cz> <20121015220354.GA11682@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, David Rientjes , KOSAKI Motohiro , KAMEZAWA Hiroyuki , Johannes Weiner , LKML On Tue, 16 Oct 2012 00:04:08 +0200 Michal Hocko wrote: > As Kosaki correctly pointed out, the glogal reclaim doesn't have this > issue because we _do_ swap on swappinnes==0 so the swap space has > to be considered. So the v2 is just acks + changelog fix. > > Changes since v1 > - drop a note about global swappiness affected as well from the > changelog > - stable needs 3.2+ rather than 3.5+ because the fe35004f has been > backported to stable > --- > >From c2ae4849f09dbfda6b61472c6dd1fd8c2fe8ac81 Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Wed, 10 Oct 2012 15:46:54 +0200 > Subject: [PATCH] memcg: oom: fix totalpages calculation for > memory.swappiness==0 > > oom_badness takes totalpages argument which says how many pages are > available and it uses it as a base for the score calculation. The value > is calculated by mem_cgroup_get_limit which considers both limit and > total_swap_pages (resp. memsw portion of it). > > This is usually correct but since fe35004f (mm: avoid swapping out > with swappiness==0) we do not swap when swappiness is 0 which means > that we cannot really use up all the totalpages pages. This in turn > confuses oom score calculation if the memcg limit is much smaller than > the available swap because the used memory (capped by the limit) is > negligible comparing to totalpages so the resulting score is too small > if adj!=0 (typically task with CAP_SYS_ADMIN or non zero oom_score_adj). > A wrong process might be selected as result. > > The problem can be worked around by checking mem_cgroup_swappiness==0 > and not considering swap at all in such a case. > > Signed-off-by: Michal Hocko > Acked-by: David Rientjes > Acked-by: Johannes Weiner > Acked-by: KOSAKI Motohiro > Acked-by: KAMEZAWA Hiroyuki > Cc: stable [3.2+] That's "Cc: ", please. It's unobvious from the changelog that a -stable backport is really needed. The bug looks pretty obscure and has been there for a long time. Realistically, is anyone likely to hurt from this? -- 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