linux-kernel - Re: [PATCH mmotm] vmscan: handle may_swap more strictly (Re: [PATCH mmotm] vmscan: fix may

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Message-ID: <28c262360906090119r6e881caq9b74028ba43567a7@mail.gmail.com>
Date:	Tue, 9 Jun 2009 17:19:20 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH mmotm] vmscan: handle may_swap more strictly (Re: [PATCH 
	mmotm] vmscan: fix may_swap handling for memcg)

On Tue, Jun 9, 2009 at 4:58 PM, KOSAKI
Motohiro<kosaki.motohiro@...fujitsu.com> wrote:
>> Hi, KOSAKI.
>>
>> As you know, this problem caused by if condition(priority) in shrink_zone.
>> Let me have a question.
>>
>> Why do we have to prevent scan value calculation when the priority is zero ?
>> As I know, before split-lru, we didn't do it.
>>
>> Is there any specific issue in case of the priority is zero ?
>
> Yes.
>
> example:
>
> get_scan_ratio() return anon:80%, file=20%. and the system have
> 10000 anon pages and 10000 file pages.
>
> shrink_zone() picked up 8000 anon pages and 2000 file pages.
> it mean 8000 file pages aren't scanned at all.
>
> Oops, it can makes OOM-killer although system have droppable file cache.
>
Hmm..Can that problem be happen in real system ?
The file ratio is big means that file lru list scanning is so big but
rotate is small.
It means file lru have few reclaimable page.

Isn't it ? I am confusing.
Could you elaborate, please if you don't mind ?

-- 
Kinds regards,
Minchan Kim
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