From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 0C9376B0044 for ; Tue, 24 Nov 2009 18:56:28 -0500 (EST) Date: Wed, 25 Nov 2009 08:49:10 +0900 From: Daisuke Nishimura Subject: Re: [BUGFIX][PATCH -mmotm] memcg: avoid oom-killing innocent task in case of use_hierarchy Message-Id: <20091125084910.16d9095d.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20091124170402.GB3365@balbir.in.ibm.com> References: <20091124145759.194cfc9f.nishimura@mxp.nes.nec.co.jp> <661de9470911240531p5e587c42w96995fde37dbd401@mail.gmail.com> <20091124230029.7245e1b8.d-nishimura@mtf.biglobe.ne.jp> <20091124170402.GB3365@balbir.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org To: balbir@linux.vnet.ibm.com Cc: Andrew Morton , LKML , linux-mm , stable , David Rientjes , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Daisuke Nishimura List-ID: On Tue, 24 Nov 2009 22:34:02 +0530, Balbir Singh wrote: > * Daisuke Nishimura [2009-11-24 23:00:29]: > > > On Tue, 24 Nov 2009 19:01:54 +0530 > > Balbir Singh wrote: > > > > > On Tue, Nov 24, 2009 at 11:27 AM, Daisuke Nishimura > > > wrote: > > > > task_in_mem_cgroup(), which is called by select_bad_process() to check whether > > > > a task can be a candidate for being oom-killed from memcg's limit, checks > > > > "curr->use_hierarchy"("curr" is the mem_cgroup the task belongs to). > > > > > > > > But this check return true(it's false positive) when: > > > > > > > > A A A A /00 A A A A A use_hierarchy == 0 A A A <- hitting limit > > > > A A A A A /00/aa A A use_hierarchy == 1 A A A <- "curr" > > > > > > > > This leads to killing an innocent task in 00/aa. This patch is a fix for this > > > > bug. And this patch also fixes the arg for mem_cgroup_print_oom_info(). We > > > > should print information of mem_cgroup which the task being killed, not current, > > > > belongs to. > > > > > > > > > > Quick Question: What happens if /00 has no tasks in it > > > after your patches? > > > > > Nothing would happen because /00 never hit its limit. > > Why not? I am talking of a scenario where /00 is set to a > limit (similar to your example) and hits its limit, but the groups > under it have no limits, but tasks. Shouldn't we be scanning > /00/aa as well? > > > > > The bug that this patch fixes is: > > > > - create a dir /00 and set some limits. > > - create a sub dir /00/aa w/o any limits, and enable hierarchy. > > - run some programs in both in 00 and 00/aa. programs in 00 should be > > big enough to cause oom by its limit. > > - when oom happens by 00's limit, tasks in 00/aa can also be killed. > > > > To be honest, the last part is fair, specifically if 00/aa has a task > that is really the heaviest task as per the oom logic. no? Are you > suggesting that only tasks in /00 should be selected by the > oom logic? > All of your comments would be rational if hierarchy is enabled in 00(it's also enabled in 00/aa automatically in this case). I'm saying about the case where it's disabled in 00 but enabled in 00/aa. In this scenario, charges by tasks in 00/aa is(and should not be) charged to 00. And oom caused by 00's limit should not affect the task in 00/aa. Regards, Daisuke Nishimura. -- 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