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Date: Tue, 24 Nov 2009 19:01:54 +0530
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Subject: Re: [BUGFIX][PATCH -mmotm] memcg: avoid oom-killing innocent task in 
	case of use_hierarchy
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
       stable <stable@kernel.org>, David Rientjes <rientjes@google.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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On Tue, Nov 24, 2009 at 11:27 AM, Daisuke Nishimura
<nishimura@mxp.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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