linux-kernel - [RFC][PATCH] split file and anonymous page queues #2

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Message-ID: <45FF3052.0@redhat.com>
Date:	Mon, 19 Mar 2007 20:52:34 -0400
From:	Rik van Riel <riel@...hat.com>
To:	linux-mm <linux-mm@...ck.org>
CC:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [RFC][PATCH] split file and anonymous page queues #2

Split the anonymous and file backed pages out onto their own pageout
queues.  This we do not unnecessarily churn through lots of anonymous
pages when we do not want to swap them out anyway.

This should (with additional tuning) be a great step forward in
scalability, allowing Linux to run well on very large systems where
scanning through the anonymous memory (on our way to the page cache
memory we do want to evict) is slowing systems down significantly.

This patch has been stress tested and seems to work, but has not
been fine tuned or benchmarked yet.  For now the swappiness parameter
can be used to tweak swap aggressiveness up and down as desired, but
in the long run we may want to simply measure IO cost of page cache
and anonymous memory and auto-adjust.

We apply pressure to each of sets of the pageout queues based on:
- the size of each queue
- the fraction of recently referenced pages in each queue,
    not counting used-once file pages
- swappiness (file IO is more efficient than swap IO)

Please take this patch for a spin and let me know what goes well
and what goes wrong.

More info on the patch can be found on:

http://linux-mm.org/PageReplacementDesign

Signed-off-by: Rik van Riel <riel@...hat.com>

Changelog:
- Fix page_anon() to put all the file pages really on the
   file list.
- Fix get_scan_ratio() to return more stable numbers, by
   properly keeping track of the scanned anon and file pages.

-- 
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.

View attachment "linux-2.6-vm-split.patch" of type "text/x-patch" (51334 bytes)