From: Christoph Hellwig <hch@lst.de>
Subject: Re: [xfs-masters] Re: Interaction between Xen and XFS: stray RW mappings
Date: Mon, 15 Oct 2007 10:31:41 +0200
Message-ID: <20071015083141.GA20851@lst.de>
References: <470FA7C3.90404@goop.org> <200710151415.07248.nickpiggin@yahoo.com.au> <4712BB05.1020701@goop.org> <200710151726.08387.nickpiggin@yahoo.com.au> <4712E1AA.501@goop.org> <20071015041133.GH995458@sgi.com> <4712EA09.6000102@goop.org> <20071015042546.GI995458@sgi.com>
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Cc: Jeremy Fitzhardinge <jeremy@goop.org>, David Chinner <dgc@sgi.com>, Nick Piggin <nickpiggin@yahoo.com.au>, xfs@oss.sgi.com, Xen-devel <xen-devel@lists.xensource.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Mark Williamson <mark.williamson@cl.cam.ac.uk>, Morten B?geskov <xen-users@morten.bogeskov.dk>
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On Mon, Oct 15, 2007 at 02:25:46PM +1000, David Chinner wrote:
> > Hm, well I saw the problem with a filesystem made with mkfs.xfs with no
> > options, so there must be at least *some* vmapping going on there.
> 
> Sorry - I should have been more precise - vmap should never be used in
> performance critical paths on default configs.  Log recovery will
> trigger vmap/vunmap usage, so this is probably what you are seeing.

The iclogs are also vmapped, but they aren't unmapped until unmount so
this optimizations doesn't matter either.