[xfs-masters] Re: Interaction between Xen and XFS: stray RW mappings

[David Chinner <dgc@xxxxxxx>]

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