linux-kernel - Re: [patch -mm 2/9 v2] oom: sacrifice child with highest badness score for parent

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Message-ID: <20100216061553.GZ5723@laptop>
Date:	Tue, 16 Feb 2010 17:15:53 +1100
From:	Nick Piggin <npiggin@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch -mm 2/9 v2] oom: sacrifice child with highest badness
 score for parent

On Mon, Feb 15, 2010 at 02:20:03PM -0800, David Rientjes wrote:
> When a task is chosen for oom kill, the oom killer first attempts to
> sacrifice a child not sharing its parent's memory instead.
> Unfortunately, this often kills in a seemingly random fashion based on
> the ordering of the selected task's child list.  Additionally, it is not
> guaranteed at all to free a large amount of memory that we need to
> prevent additional oom killing in the very near future.
> 
> Instead, we now only attempt to sacrifice the worst child not sharing its
> parent's memory, if one exists.  The worst child is indicated with the
> highest badness() score.  This serves two advantages: we kill a
> memory-hogging task more often, and we allow the configurable
> /proc/pid/oom_adj value to be considered as a factor in which child to
> kill.
> 
> Reviewers may observe that the previous implementation would iterate
> through the children and attempt to kill each until one was successful
> and then the parent if none were found while the new code simply kills
> the most memory-hogging task or the parent.  Note that the only time
> oom_kill_task() fails, however, is when a child does not have an mm or
> has a /proc/pid/oom_adj of OOM_DISABLE.  badness() returns 0 for both
> cases, so the final oom_kill_task() will always succeed.
> 
> Acked-by: Rik van Riel <riel@...hat.com>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
Acked-by: Nick Piggin <npiggin@...e.de>
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