From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx104.postini.com [74.125.245.104]) by kanga.kvack.org (Postfix) with SMTP id 6C72C6B002B for ; Thu, 11 Oct 2012 08:20:50 -0400 (EDT) Date: Thu, 11 Oct 2012 08:20:37 -0400 From: Johannes Weiner Subject: Re: [PATCH] memcg: oom: fix totalpages calculation for memory.swappiness==0 Message-ID: <20121011122037.GE31863@cmpxchg.org> References: <20121011085038.GA29295@dhcp22.suse.cz> <1349945859-1350-1-git-send-email-mhocko@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1349945859-1350-1-git-send-email-mhocko@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , linux-mm@kvack.org, David Rientjes , KOSAKI Motohiro , KAMEZAWA Hiroyuki , LKML On Thu, Oct 11, 2012 at 10:57:39AM +0200, Michal Hocko wrote: > 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 same issue exists for the global oom killer as well but it is not > that problematic as the amount of the RAM is usually much bigger than > the swap space. > > 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 > Cc: stable [3.5+] I also don't think it's hackish, the limit depends very much on whether reclaim can swap, so it's natural that swappiness shows up here. Acked-by: Johannes Weiner -- 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