linux-kernel - Re: Why active list and inactive list?

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Date:	Mon, 22 Jan 2007 21:17:34 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Christoph Lameter <clameter@....com>
CC:	Balbir Singh <balbir@...ibm.com>,
	Andrea Arcangeli <andrea@...e.de>,
	Niki Hammler <mailinglists@...aq.net>,
	linux-kernel@...r.kernel.org,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: Why active list and inactive list?

Christoph Lameter wrote:
> On Mon, 22 Jan 2007, Rik van Riel wrote:
> 
>> It would be really nice if we came up with a page replacement
>> algorithm that did not need many extra heuristics to make it
>> work...
> 
> I guess the "clock" type algorithms are the most promising in that 
> area. What happened to all those advanced page replacement endeavors? 
> What is the most promising of those? You seem to have done a lot of work 
> on those.

CLOCK-Pro seems the most promising algorithm, because it can
act well both as a first level cache (operating system running
applications) and as a second level cache (operating system
running as a file server), because it tracks both recency and
frequency well.

However, there are a few unanswered questions on clock-pro.

The big one is how we are to do some background aging in a
clock-pro system, so referenced bits don't just pile up when
the VM has enough memory - otherwise we might not know the
right pages to evict when a new process starts up and starts
allocating lots of memory.

At least we've solved the problems of keeping track of the
recently evicted pages in a cheap way, and balancing the
pressure/hotness of different caches against each other.

-- 
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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