linux-kernel - Re: Cleancache and shared filesystems

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Message-ID: <20110531215443.GC31742@noexit.corp.google.com>
Date:	Tue, 31 May 2011 14:54:43 -0700
From:	Joel Becker <jlbec@...lplan.org>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	Steven Whitehouse <swhiteho@...hat.com>,
	linux-kernel@...r.kernel.org,
	Sunil Mushran <sunil.mushran@...cle.com>
Subject: Re: Cleancache and shared filesystems

On Tue, May 31, 2011 at 07:51:36AM -0700, Dan Magenheimer wrote:
> > Hey Dan,
> > 	Steven makes a good point here.  ocfs2 could also take advantage
> > of local filesystem behavior when running in local mode.
> 
> I guess the semantics need to be more clearly defined
> (or perhaps changed if the shared-fs community wants),
> but if cleancache_init_shared_fs is called only by
> a single node, cleancache still enables all the same
> functionality** as cleancache_init_fs. 

	I don't see the ** reference in the footnotes ;-)  You're saying
that, for a single caller, you will properly keep the pagecache bits
around in cleancache as you shrink the balloon and give them back when
requested?  So an ocfs2 calling cleancache_init_share_fs() in only one
VM will have the same page lifetimes (including life inside cleancache
but not in guest pagecache) as a similar ext3?  If so, there are no
changes needed at all.

> I'm not sure I fully understand the semantics of
> local mode though, so please clarify if you think
> I am wrong or misunderstanding your point.

	ocfs2 local mode means that it is not a cluster filesystem.  The
cluster services are not enabled, and ocfs2 behaves like xfs/extN/btrfs.

Joel

-- 

"Lately I've been talking in my sleep.
 Can't imagine what I'd have to say.
 Except my world will be right
 When love comes back my way."

			http://www.jlbec.org/
			jlbec@...lplan.org
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