linux-kernel - Re: [PATCH v2] vmscan: limit concurrent reclaimers in shrink

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Date:	Sun, 13 Dec 2009 23:09:18 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	lwoodman@...hat.com, akpm@...ux-foundation.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vmscan: limit concurrent reclaimers in shrink_zone

On 12/13/2009 07:14 PM, Minchan Kim wrote:

> On Sat, Dec 12, 2009 at 6:46 AM, Rik van Riel<riel@...hat.com>  wrote:

>> If too many processes are active doing page reclaim in one zone,
>> simply go to sleep in shrink_zone().

> I am worried about one.
>
> Now, we can put too many processes reclaim_wait with NR_UNINTERRUBTIBLE state.
> If OOM happens, OOM will kill many innocent processes since
> uninterruptible task
> can't handle kill signal until the processes free from reclaim_wait list.
>
> I think reclaim_wait list staying time might be long if VM pressure is heavy.
> Is this a exaggeration?
>
> If it is serious problem, how about this?
>
> We add new PF_RECLAIM_BLOCK flag and don't pick the process
> in select_bad_process.

A simpler solution may be to use sleep_on_interruptible, and
simply have the process continue into shrink_zone() if it
gets a signal.

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