Re: [Xen-devel] Tagging Xen 4.0.0 first release candidate / pygrub dom0 caching bug

[Daniel Stodden <daniel.stodden@xxxxxxxxxx>]

On Thu, 2010-01-21 at 13:44 -0500, Daniel Stodden wrote:
> On Thu, 2010-01-21 at 07:28 -0500, Pasi KÃrkkÃinen wrote:
> > On Wed, Jan 06, 2010 at 03:50:05PM +0200, Pasi KÃrkkÃinen wrote:
> > > On Tue, Jan 05, 2010 at 06:42:05AM +0000, Keir Fraser wrote:
> > > > I plan to tag -rc1 later this week. If you have any outstanding patches,
> > > > please send them to the list now.
> > > > 
> > > 
> > > Hmm.. I just remembered this pygrub bug:
> > > https://bugzilla.redhat.com/show_bug.cgi?id=466681
> > > 
> > > pygrub doesn't use O_DIRECT so sometimes it gets old information
> > > from dom0 kernel cache - and fails to use the updated domU grub.conf.
> > > 
> > > Redhat seems to have patches available for testing.. not for
> > > xen-unstable though.
> > > 
> > > I've personally hit this bug many times.
> > > 
> > 
> > It seems Redhat guys have a fix available.. they fixed the problem by 
> > patching dom0 kernel blkback.
> > 
> > More details about the fix here:
> > https://bugzilla.redhat.com/show_bug.cgi?id=466681
> > 
> > Should this be applied to 2.6.18-xen and pv_ops dom0 kernels aswell? 
> 
> Only to 2.6.18. 
> 
> It's obsolete after 2.6.27.
> O_DIRECT gained page cache invalidation in the meantime.

Aiiee, sorry. I guess this one only applies to tapdisks. The page cache
invalidation only covers the filemap. That obviously won't fix blkback
bios on raw devices.

Ian Campbell recently noted he came across a different fix, which adds
direct-io to e2fsprogs.

http://www.spinics.net/lists/linux-ext4/msg16992.html

Any opinions on the tradeoff?

Daniel





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