Re: [GIT PULL] block/io bits for 2.6.35-rc

[Mark Lord]

On 10/06/10 12:44 PM, Brian Bloniarz wrote:
> On 06/10/2010 12:25 PM, Jens Axboe wrote:
> > On 2010-06-10 17:55, Linus Torvalds wrote:
> > > On Thu, Jun 10, 2010 at 6:44 AM, Jens Axboe<jaxboe@xxxxxxxxxxxx>  wrote:
> > > > - A set of patches fixing the WB_SYNC_NONE writeback from Christoph. So
> > > >   we should finally have both functional and working WB_SYNC_NONE from
> > > >   umount context.
> > >
> > > I _really_ think this is too late, considering how broken it has been.
> > > We already reverted the WB_SYNC_NONE things exactly because it didn't
> > > work, didn't we? I'm going to be off-line in two days, and this part
> > > of the pull request really makes me nervous, if only simply because of
> > > the history of it all (ie it's always been broken, why shouldn't it be
> > > broken now?).
> > >
> > > IOW, that's a lot of scary changes, that have historically not been
> > > safe or sufficiently tested, and have caused problems for various
> > > filesystems. Convince me why they should suddenly be ok to merge?
> >
> > I agree, it's late and it makes me nervous too. I had them cook for
> > a day, didn't see any problems. And Christoph would not send it in
> > unless it passes at least xfs qa, which is what found the problems
> > last time (the ones we reverted).
> >
> > It's fixing a regression where umount takes a LONG time if you have
> > a lot of dirty inodes, since it basically degenerates to a data
> > integrity writeback instead of a simple WB_SYNC_NONE. If it wasn't
> > fixing a nasty regression (the distros are all wanting a real fix
> > for this, it's a user problem), I would not be submitting this code
> > at this point in time.
>
> Reinforcing that last point: from what I could figure out, Fedora 13
> is shipping the buggy WB_SYNC_NONE patch currently. Ubuntu 10.04 is
> shipping an in-kernel workaround that has serious performance
> drawbacks.
>
> https://bugzilla.kernel.org/show_bug.cgi?id=15906 has links to the
> downstream bugs.
..

Jens, this bug has been biting my servers badly here for the past
few months -- umount after a backup (from ext4 to ext4) takes 3-4 minutes
instead of the expected 3-4 seconds.

Is there a patch file for this against 2.6.34 that I (and others) could use?

Thanks
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