linux-kernel - Re: Device loses barrier support (was: Fixed patch for simple barriers.)

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Date:	Sun, 7 Dec 2008 15:17:11 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	xfs@....sgi.com, Alasdair G Kergon <agk@...hat.com>,
	Andi Kleen <andi-suse@...stfloor.org>,
	Milan Broz <mbroz@...hat.com>
Subject: Re: Device loses barrier support (was: Fixed patch for simple
	barriers.)

On Thu, Dec 04, 2008 at 11:45:44AM -0500, Mikulas Patocka wrote:
> > The write block with barrier bit varies, jbd/gfs2 do it synchronously
> > too and xfs does it asynchronously (with io done callbacks), but
> 
> And how does xfs preserve write ordering, if the barrier asynchronously 
> fails with -EOPNOTSUPP and there are other writes submitted after the 
> barrier?

Doesn't matter. XFS executes journal state changes during the I/O
completion callbacks a layer above this resubmit code. Hence,
if the I/O is resubmitted before the completion callbacks are
run, it just appears that the I/O has taken longer than expected
and the state change is delayed....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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