linux-kernel - Re: [PATCH 2/3][v2] vmstat: add anon_scan

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Message-ID: <4B53C466.4010103@redhat.com>
Date:	Sun, 17 Jan 2010 21:16:06 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/3][v2] vmstat: add anon_scan_ratio field to zoneinfo

On 01/17/2010 09:10 PM, Minchan Kim wrote:

> Absoultely right. I missed that. Thanks.
> get_scan_ratio used lru_lock to get reclaim_stat->recent_xxxx.
> But, it doesn't used lru_lock to get ap/fp.
>
> Is it intentional? I think you or Rik know it. :)
> I think if we want to get exact value, we have to use lru_lock until
> getting ap/fp.
> If it isn't, we don't need lru_lock when we get the reclaim_stat->recent_xxxx.
>
> What do you think about it?

This is definately not intentional.

Getting race conditions in this code could throw off the
statistics by a factor 2.  I do not know how serious that
would be for the VM or whether (and how quickly) it would
self correct.

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