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

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Message-ID: <28c262360906090135x3382456by3518434a9939002b@mail.gmail.com>
Date:	Tue, 9 Jun 2009 17:35:09 +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>,
	Rik van Riel <riel@...hat.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 5:24 PM, KOSAKI
Motohiro<kosaki.motohiro@...fujitsu.com> wrote:
>> 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 ?
>
> hm, ok, my example was wrong.
> I intention is, if there are droppable file-back pages (althout only 1 page),
> OOM-killer shouldn't occuer.
>
> many or few is unrelated.
>

I am not sure that is effective.
Have you ever met this problem in real situation ?

BTW, I have to dive into code. :)
Thanks for spending valuable time for commenting

-- 
Kinds regards,
Minchan Kim
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