linux-kernel - RE: [PATCH V3 0/8] Cleancache: overview

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Date:	Fri, 23 Jul 2010 14:17:31 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	ngupta@...are.org, akpm@...ux-foundation.org,
	Chris Mason <chris.mason@...cle.com>, viro@...iv.linux.org.uk,
	adilger@....com, tytso@....edu, mfasheh@...e.com,
	Joel Becker <joel.becker@...cle.com>, matthew@....cx,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	ocfs2-devel@....oracle.com, linux-mm@...ck.org, jeremy@...p.org,
	JBeulich@...ell.com, Kurt Hackel <kurt.hackel@...cle.com>,
	npiggin@...e.de, Dave Mccracken <dave.mccracken@...cle.com>,
	riel@...hat.com, avi@...hat.com,
	Konrad Wilk <konrad.wilk@...cle.com>
Subject: RE: [PATCH V3 0/8] Cleancache: overview

> > 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.
> 
> Hi Christoph --
> 
> Thanks very much for the quick (instantaneous?) reply!
> 
> > 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.
> 
> 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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