linux-kernel - Re: [PATCH 02/12] oom: introduce find_lock_task

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Message-ID: <AANLkTikF0EAmKsBx28-paTg7DUdOiHLz5KHJbzLW_OBS@mail.gmail.com>
Date:	Thu, 3 Jun 2010 15:12:10 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Oleg Nesterov <oleg@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 02/12] oom: introduce find_lock_task_mm() to fix !mm false 
	positives

On Thu, Jun 3, 2010 at 2:50 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
> From: Oleg Nesterov <oleg@...hat.com>
>
> Almost all ->mm == NUL checks in oom_kill.c are wrong.
>
> The current code assumes that the task without ->mm has already
> released its memory and ignores the process. However this is not
> necessarily true when this process is multithreaded, other live
> sub-threads can use this ->mm.
>
> - Remove the "if (!p->mm)" check in select_bad_process(), it is
>  just wrong.
>
> - Add the new helper, find_lock_task_mm(), which finds the live
>  thread which uses the memory and takes task_lock() to pin ->mm
>
> - change oom_badness() to use this helper instead of just checking
>  ->mm != NULL.
>
> - As David pointed out, select_bad_process() must never choose the
>  task without ->mm, but no matter what badness() returns the
>  task can be chosen if nothing else has been found yet.
>
> Note! This patch is not enough, we need more changes.
>
>        - badness() was fixed, but oom_kill_task() still ignores
>          the task without ->mm
>
> This will be addressed later.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

Could you see my previous comment?
http://lkml.org/lkml/2010/6/2/325
Anyway, I added my review sign

Reviewed-by: Minchan Kim <minchan.kim@...il.com>
-- 
Kind regards,
Minchan Kim
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