linux-kernel - Re: [PATCH 4/5] oom: don't kill random process

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Message-ID: <4DDB1028.7000600@jp.fujitsu.com>
Date:	Tue, 24 May 2011 10:55:52 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	rientjes@...gle.com
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, caiqian@...hat.com, hughd@...gle.com,
	kamezawa.hiroyu@...fujitsu.com, minchan.kim@...il.com,
	oleg@...hat.com
Subject: Re: [PATCH 4/5] oom: don't kill random process

>>> This is unnecessary and just makes the oom killer egregiously long.  We
>>> are already diagnosing problems here at Google where the oom killer holds
>>> tasklist_lock on the readside for far too long, causing other cpus waiting
>>> for a write_lock_irq(&tasklist_lock) to encounter issues when irqs are
>>> disabled and it is spinning.  A second tasklist scan is simply a
>>> non-starter.
>>>
>>>    [ This is also one of the reasons why we needed to introduce
>>>      mm->oom_disable_count to prevent a second, expensive tasklist scan. ]
>>
>> You misunderstand the code. Both select_bad_process() and oom_kill_process()
>> are under tasklist_lock(). IOW, no change lock holding time.
>>
>
> A second iteration through the tasklist in select_bad_process() will
> extend the time that tasklist_lock is held, which is what your patch does.

It never happen usual case. Plz think when happen all process score = 1.

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