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

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Message-Id: <20090609164850.DD73.A69D9226@jp.fujitsu.com>
Date:	Tue,  9 Jun 2009 16:58:36 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	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)

> 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.



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