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Date:	Sat, 16 Apr 2011 03:54:39 +0900
From:	OGAWA Hirofumi <>
To:	Dan Magenheimer <>
Subject: Re: [PATCH V8 1/8] mm/fs: cleancache documentation

Dan Magenheimer <> writes:

> [PATCH V8 1/8] mm/fs: cleancache documentation
> This patchset introduces cleancache, an optional new feature exposed
> by the VFS layer that potentially dramatically increases page cache
> effectiveness for many workloads in many environments at a negligible
> cost.  It does this by providing an interface to transcendent memory,
> which is memory/storage that is not otherwise visible to and/or directly
> addressable by the kernel.
> Instead of being discarded, hooks in the reclaim code "put" clean
> pages to cleancache.  Filesystems that "opt-in" may "get" pages 
> from cleancache that were previously put, but pages in cleancache are 
> "ephemeral", meaning they may disappear at any time. And the size
> of cleancache is entirely dynamic and unknowable to the kernel.
> Filesystems currently supported by this patchset include ext3, ext4,
> btrfs, and ocfs2.  Other filesystems (especially those built entirely
> on VFS) should be easy to add, but should first be thoroughly tested to
> ensure coherency.
> Details and a FAQ are provided in Documentation/vm/cleancache.txt
> This first patch of eight in this cleancache series only adds two
> new documentation files.

Another question: why can't this enable/disable per sb, e.g. via mount
options? (I have the interest the cache stuff like this by SSD on
physical systems like dragonfly's swapcache.)

Well, anyway, I guess force enabling this for mostly unused sb can just
add cache-write overhead and call for unpleasing reclaim to backend
(because of limited space of backend) like updatedb.

And already there is in FAQ though, I also have interest about async
interface because of SDD backend (I'm not sure for now though). Is there
any plan like SSD backend?

OGAWA Hirofumi <>
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