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

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Date:	Mon, 18 Jan 2010 11:25:10 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Rik van Riel <riel@...hat.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 Mon, Jan 18, 2010 at 11:16 AM, Rik van Riel <riel@...hat.com> wrote:
> 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.

Okay. How about making patch to get exact ap/fp?
Although it were not serious or fast recoverable, I think it would be better
to protect lru_lock for consistency if lru_lock isn't big contention lock.

>
> --
> All rights reversed.
>



-- 
Kind regards,
Minchan Kim
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