linux-kernel - Re: [PATCH] vmscan: bail out of page reclaim after swap_cluster

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Message-ID: <492BFE6F.5090902@redhat.com>
Date:	Tue, 25 Nov 2008 08:32:31 -0500
From:	Rik van Riel <riel@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, mel@....ul.ie,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] vmscan: bail out of page reclaim after swap_cluster_max
 pages

KOSAKI Motohiro wrote:
>> Sometimes the VM spends the first few priority rounds rotating back
>> referenced pages and submitting IO.  Once we get to a lower priority,
>> sometimes the VM ends up freeing way too many pages.
>>
>> The fix is relatively simple: in shrink_zone() we can check how many
>> pages we have already freed, direct reclaim tasks break out of the
>> scanning loop if they have already freed enough pages and have reached
>> a lower priority level.
>>
>> However, in order to do this we do need to know how many pages we already
>> freed, so move nr_reclaimed into scan_control.
>>
>> Signed-off-by: Rik van Riel <riel@...hat.com>
>> ---
>> Kosaki, this should address the zone scanning pressure issue.
> 
> hmmmm. I still don't like the behavior when priority==DEF_PRIORITY.
> but I also should explain by code and benchmark.

Well, the behaviour when priority==DEF_PRIORITY is the
same as the kernel's behaviour without the patch...

> therefore, I'll try to mesure this patch in this week.

Looking forward to it.

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