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Date: Sun, 7 Dec 2008 15:17:11 +1100
From: Dave Chinner <david@fromorbit.com>
Subject: Re: Device loses barrier support (was: Fixed patch for simple
	barriers.)
Message-ID: <20081207041711.GA22525@disturbed>
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To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Andi Kleen <andi-suse@firstfloor.org>, linux-kernel@vger.kernel.org, xfs@oss.sgi.com, Andi Kleen <andi@firstfloor.org>, Alasdair G Kergon <agk@redhat.com>, Milan Broz <mbroz@redhat.com>

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@fromorbit.com

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