linux-kernel - Re: [PATCH 0/3] readahead drop behind and size adjustment

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Message-ID: <46A76C09.6000602@redhat.com>
Date:	Wed, 25 Jul 2007 11:28:09 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Eric St-Laurent <ericstl34@...patico.ca>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Fengguang Wu <fengguang.wu@...il.com>,
	Dave Jones <davej@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tim Pepper <lnxninja@...ibm.com>,
	Chris Snook <csnook@...hat.com>
Subject: Re: [PATCH 0/3] readahead drop behind and size adjustment

Nick Piggin wrote:

> What *I* think is supposed to happen is that newly read in pages get
> put on the inactive list, and unless they get accessed againbefore
> being reclaimed, they are allowed to fall off the end of the list
> without disturbing active data too much.
> 
> I think there is a missing piece here, that we used to ease the reclaim
> pressure off the active list when the inactive list grows relatively
> much larger than it (which could indicate a lot of use-once pages in
> the system).
> 
> Andrew got rid of that logic for some reason which I don't know, but I
> can't see that use-once would be terribly effective today (so your
> results don't surprise me too much).

I suspect that reason is that use-once works great for
page cache pages, but anonymous pages share the same
LRUs and need a more balanced aging approach.

The result: an LRU list that works ok for both types
of pages most of the time, but falls over in some
workloads.

-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
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