linux-kernel - Re: [RFC][PATCH] split file and anonymous page queues #3

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Message-ID: <46011EF6.3040704@redhat.com>
Date:	Wed, 21 Mar 2007 08:03:02 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Nikita Danilov <nikita@...sterfs.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] split file and anonymous page queues #3

Rik van Riel wrote:
> Nikita Danilov wrote:
> 
>> Probably I am missing something, but I don't see how that can help. For
>> example, suppose (for simplicity) that we have swappiness of 100%, and
>> that fraction of referenced anon pages gets slightly less than of file
>> pages. get_scan_ratio() increases anon_percent, and shrink_zone() starts
>> scanning anon queue more aggressively. As a result, pages spend less
>> time there, and have less chance of ever being accessed, reducing
>> fraction of referenced anon pages further, and triggering further
>> increase in the amount of scanning, etc. Doesn't this introduce positive
>> feed-back loop?
> 
> It's a possibility, but I don't think it will be much of an
> issue in practice.
> 
> If it is, we can always use refaults as a correcting
> mechanism - which would have the added benefit of being
> able to do streaming IO without putting any pressure on
> the active list, essentially clock-pro replacement with
> just some tweaks to shrink_list()...

As an aside, due to the use-once algorithm file pages are at a
natural disadvantage already.  I believe it would be really
hard to construct a workload where anon pages suffer the positive
feedback loop you describe...

-- 
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the best in the world, and those who believe it already is.  Each group
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