linux-kernel - Re: [BUGFIX][PATCH -mmotm] memcg: avoid oom-killing innocent task in case of use

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Date:	Tue, 24 Nov 2009 19:01:54 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, stable <stable@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [BUGFIX][PATCH -mmotm] memcg: avoid oom-killing innocent task in 
	case of use_hierarchy

On Tue, Nov 24, 2009 at 11:27 AM, Daisuke Nishimura
<nishimura@....nes.nec.co.jp> 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:
>
>        <some path>/00          use_hierarchy == 0      <- hitting limit
>          <some path>/00/aa     use_hierarchy == 1      <- "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 <some path>/00 has no tasks in it
after your patches?

Balbir
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