linux-kernel - Re: Interaction between Xen and XFS: stray RW mappings

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Message-ID: <20071015042546.GI995458@sgi.com>
Date:	Mon, 15 Oct 2007 14:25:46 +1000
From:	David Chinner <dgc@....com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	David Chinner <dgc@....com>, Nick Piggin <nickpiggin@...oo.com.au>,
	xfs@....sgi.com, Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mark Williamson <mark.williamson@...cam.ac.uk>,
	Morten Bøgeskov <xen-users@...ten.bogeskov.dk>,
	xfs-masters@....sgi.com
Subject: Re: Interaction between Xen and XFS: stray RW mappings

On Sun, Oct 14, 2007 at 09:18:17PM -0700, Jeremy Fitzhardinge wrote:
> David Chinner wrote:
> > With defaults - little effect as vmap should never be used. It's
> > only when you start using larger block sizes for metadata that this
> > becomes an issue. The CONFIG_XEN workaround should be fine until we
> > get a proper vmap cache....
> 
> 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.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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