linux-kernel - Re: [PATCH 2/4] oom: kill younger process first

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Message-ID: <BANLkTi=ya1rAqC+nMPHkBaMsoXpsCeHH=w@mail.gmail.com>
Date:	Thu, 12 May 2011 10:30:45 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	CAI Qian <caiqian@...hat.com>, avagin@...il.com,
	Andrey Vagin <avagin@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 2/4] oom: kill younger process first

Hi Kame,

On Thu, May 12, 2011 at 9:52 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Tue, 10 May 2011 17:15:01 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
>
>> This patch introduces do_each_thread_reverse() and
>> select_bad_process() uses it. The benefits are two,
>> 1) oom-killer can kill younger process than older if
>> they have a same oom score. Usually younger process
>> is less important. 2) younger task often have PF_EXITING
>> because shell script makes a lot of short lived processes.
>> Reverse order search can detect it faster.
>>
>> Reported-by: CAI Qian <caiqian@...hat.com>
>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>
> IIUC, for_each_thread() can be called under rcu_read_lock() but
> for_each_thread_reverse() must be under tasklist_lock.

Just out of curiosity.
You mentioned it when I sent forkbomb killer patch. :)
>From at that time, I can't understand why we need holding
tasklist_lock not rcu_read_lock. Sorry for the dumb question.

At present, it seems that someone uses tasklist_lock and others uses
rcu_read_lock. But I can't find any rule for that.

Could you elaborate it, please?
Doesn't it need document about it?

-- 
Kind regards,
Minchan Kim
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