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Re: [PATCH 1/1] xfs: serialise unaligned direct IOs

To: Amit Sahrawat <amit.sahrawat83@xxxxxxxxx>
Subject: Re: [PATCH 1/1] xfs: serialise unaligned direct IOs
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 11 Jan 2012 06:34:28 -0500
Cc: Alex Elder <aelder@xxxxxxx>, xfs masters <xfs-masters@xxxxxxxxxxx>, xfs <xfs@xxxxxxxxxxx>, linux kernel <linux-kernel@xxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
In-reply-to: <1325845990-5664-1-git-send-email-amit.sahrawat83@xxxxxxxxx>
References: <1325845990-5664-1-git-send-email-amit.sahrawat83@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
> +     /*
> +      * In most cases the direct IO writes will be done with IOLOCK_SHARED
> +      * allowing them to be done in parallel with reads and other direct IO
> +      * writes. However,if the IO is not aligned to filesystem blocks, the
> +      * direct IO layer needs to do sub-block zeroing and that requires
> +      * serialisation against other direct IOs to the same block. In this
> +      * case we need to serialise the submission of the unaligned IOs so
> +      * that we don't get racing block zeroing in the dio layer.
> +      * To avoid the problem with aio, we also need to wait for outstanding
> +      * IOs to complete so that unwritten extent conversion is completed
> +      * before we try to map the overlapping block. This is currently
> +      * implemented by hitting it with a big hammer (i.e. xfs_ioend_wait()).
> +      */
> +

This comment is lacking one level of indentation, that's because the old
kernel is missing the split of xfs_file_aio_write that reduces one level
of indentation.

Otherwise the backport looks fine, please send it to
stable@xxxxxxxxxxxxxxx, with a [PATCH 0/0] coverletter stating it's for
2.6.35-stable.

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