From: Dan Magenheimer <dan.magenheimer@oracle.com>
Subject: RE: [PATCH V3 0/8] Cleancache: overview
Date: Fri, 23 Jul 2010 14:17:31 -0700 (PDT)
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Cc: ngupta@vflare.org, akpm@linux-foundation.org,
        Chris Mason
 <chris.mason@oracle.com>, viro@zeniv.linux.org.uk,
        adilger@sun.com, tytso@mit.edu, mfasheh@suse.com,
        Joel Becker <joel.becker@oracle.com>, matthew@wil.cx,
        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
        ocfs2-devel@oss.oracle.com, linux-mm@kvack.org, jeremy@goop.org,
        JBeulich@novell.com, Kurt Hackel <kurt.hackel@oracle.com>,
        npiggin@suse.de, Dave Mccracken <dave.mccracken@oracle.com>,
        riel@redhat.com, avi@redhat.com, Konrad Wilk <konrad.wilk@oracle.com>
To: Christoph Hellwig <hch@infradead.org>
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> > On Fri, Jul 23, 2010 at 06:58:03AM -0700, Dan Magenheimer wrote:
> > > CHRISTOPH AND ANDREW, if you disagree and your concerns have
> > > not been resolved, please speak up.
>=20
> Hi Christoph --
>=20
> Thanks very much for the quick (instantaneous?) reply!
>=20
> > Anything that need modification of a normal non-shared fs is utterly
> > broken and you'll get a clear NAK, so the propsal before is a good
> > one.
>=20
> No, the per-fs opt-in is very sensible; and its design is
> very minimal.

Not to belabor the point, but maybe the right way to think about
this is:

Cleancache is a new optional feature provided by the VFS layer
that potentially dramatically increases page cache effectiveness
for many workloads in many environments at a negligible cost.

Filesystems that are well-behaved and conform to certain restrictions
can utilize cleancache simply by making a call to cleancache_init_fs
at mount time.  Unusual, misbehaving, or poorly layered filesystems
must either add additional hooks and/or undergo extensive additional
testing... or should just not enable the optional cleancache.

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