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

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Message-ID: <20071015041133.GH995458@sgi.com>
Date:	Mon, 15 Oct 2007 14:11:33 +1000
From:	David Chinner <dgc@....com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, David Chinner <dgc@....com>,
	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 08:42:34PM -0700, Jeremy Fitzhardinge wrote:
> Nick Piggin wrote:
> >  That's not going to
> > happen for at least a cycle or two though, so in the meantime maybe
> > an ifdef for that XFS vmap batching code would help?
> >   
> 
> For now I've proposed a patch to simply eagerly vunmap everything when
> CONFIG_XEN is set.  It certainly works, but I don't have a good feel for
> how much of a performance hit that imposes on XFS.

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....

Cheers,

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