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Date:	Fri, 30 Mar 2012 13:18:44 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Jeff Moyer <jmoyer@...hat.com>
CC:	linux-fsdevel@...r.kernel.org, hch@...radead.org,
	linux-ext4@...r.kernel.org, jack@...e.cz, xfs@....sgi.com
Subject: Re: [PATCH 5/7] xfs: honor the O_SYNC flag for aysnchronous direct
 I/O requests

On 3/29/12 5:05 PM, Jeff Moyer wrote:
> Hi,
> 
> If a file is opened with O_SYNC|O_DIRECT, the drive cache does not get
> flushed after the write completion for AIOs.  This patch attempts to fix
> that problem by marking an I/O as requiring a cache flush in endio
> processing, and then issuing the cache flush after any unwritten extent
> conversion is done.
> 
> Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
> ---
>  fs/xfs/xfs_aops.c  |  108 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  fs/xfs/xfs_mount.h |    1 +
>  fs/xfs/xfs_super.c |    8 ++++
>  3 files changed, 116 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 0dbb9e7..6ef8f7a 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -170,6 +170,58 @@ xfs_setfilesize(
>  }
>  
>  /*
> + * In the case of synchronous, AIO, O_DIRECT writes, we need to flush
> + * the disk cache when the I/O is complete.
> + */
> +STATIC bool
> +xfs_ioend_needs_cache_flush(
> +	struct xfs_ioend	*ioend)
> +{
> +	struct xfs_inode *ip = XFS_I(ioend->io_inode);
> +	struct xfs_mount *mp = ip->i_mount;
> +
> +	if (!ioend->io_isasync)
> +		return false;
> +
> +	if (!(mp->m_flags & XFS_MOUNT_BARRIER))
> +		return false;
> +
> +	return (IS_SYNC(ioend->io_inode) ||
> +		(ioend->io_iocb->ki_filp->f_flags & O_DSYNC));
> +}
> +
> +STATIC void
> +xfs_end_io_flush(
> +	struct bio	*bio,
> +	int		error)
> +{
> +	struct xfs_ioend *ioend = bio->bi_private;
> +
> +	if (error && ioend->io_result > 0)
> +		ioend->io_result = error;
> +
> +	xfs_destroy_ioend(ioend);
> +	bio_put(bio);
> +}
> +
> +/*
> + * Issue a WRITE_FLUSH to the specified device.
> + */
> +STATIC void
> +xfs_ioend_flush_cache(
> +	struct xfs_ioend	*ioend,
> +	xfs_buftarg_t		*targp)
> +{
> +	struct bio *bio;
> +
> +	bio = bio_alloc(GFP_KERNEL, 0);
> +	bio->bi_end_io = xfs_end_io_flush;
> +	bio->bi_bdev = targp->bt_bdev;
> +	bio->bi_private = ioend;
> +	submit_bio(WRITE_FLUSH, bio);
> +}
> +
> +/*
>   * Schedule IO completion handling on the final put of an ioend.
>   *
>   * If there is no work to do we might as well call it a day and free the
> @@ -186,11 +238,61 @@ xfs_finish_ioend(
>  			queue_work(mp->m_unwritten_workqueue, &ioend->io_work);
>  		else if (ioend->io_append_trans)
>  			queue_work(mp->m_data_workqueue, &ioend->io_work);
> +		else if (xfs_ioend_needs_cache_flush(ioend))
> +			queue_work(mp->m_flush_workqueue, &ioend->io_work);
>  		else
>  			xfs_destroy_ioend(ioend);
>  	}
>  }
>  
> +STATIC void
> +xfs_ioend_force_cache_flush(
> +	xfs_ioend_t	*ioend)
> +{
> +	struct xfs_inode *ip = XFS_I(ioend->io_inode);
> +	struct xfs_mount *mp = ip->i_mount;
> +	xfs_lsn_t	lsn = 0;
> +	int		err = 0;
> +	int		log_flushed = 0;
> +
> +	/*
> +	 * Check to see if we need to sync metadata.  If so,
> +	 * perform a log flush.  If not, just flush the disk
> +	 * write cache for the data disk.
> +	 */
> +	if (IS_SYNC(ioend->io_inode) ||
> +	    (ioend->io_iocb->ki_filp->f_flags & __O_SYNC)) {
> +		/*
> +		 * TODO: xfs_blkdev_issue_flush and _xfs_log_force_lsn
> +		 * are synchronous, and so will block the I/O
> +		 * completion work queue.
> +		 */
> +		/*
> +		 * If the log device is different from the data device,
> +		 * be sure to flush the cache on the data device
> +		 * first.
> +		 */
> +		if (mp->m_logdev_targp != mp->m_ddev_targp)
> +			xfs_blkdev_issue_flush(mp->m_ddev_targp);
> +
> +		xfs_ilock(ip, XFS_ILOCK_SHARED);
> +		if (xfs_ipincount(ip))
> +			lsn = ip->i_itemp->ili_last_lsn;
> +		xfs_iunlock(ip, XFS_ILOCK_SHARED);
> +		if (lsn)
> +			err = _xfs_log_force_lsn(mp, lsn, XFS_LOG_SYNC,
> +						 &log_flushed);
> +		if (err && ioend->io_result > 0)
> +			ioend->io_result = err;

Careful you don't get burned by _xfs_log_force_lsn returning positive
errors here...

-Eric

> +		if (err || log_flushed)
> +			xfs_destroy_ioend(ioend);
> +		else
> +			xfs_ioend_flush_cache(ioend, mp->m_logdev_targp);
> +	} else
> +		/* data sync only, flush the disk cache */
> +		xfs_ioend_flush_cache(ioend, mp->m_ddev_targp);
> +}
> +
>  /*
>   * IO write completion.
>   */
> @@ -243,7 +345,11 @@ xfs_end_io(
>  	}
>  
>  done:
> -	xfs_destroy_ioend(ioend);
> +	/* the honoring of O_SYNC has to be done last */
> +	if (xfs_ioend_needs_cache_flush(ioend))
> +		xfs_ioend_force_cache_flush(ioend);
> +	else
> +		xfs_destroy_ioend(ioend);
>  }
>  
>  /*
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 9eba738..e406204 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -214,6 +214,7 @@ typedef struct xfs_mount {
>  
>  	struct workqueue_struct	*m_data_workqueue;
>  	struct workqueue_struct	*m_unwritten_workqueue;
> +	struct workqueue_struct *m_flush_workqueue;
>  } xfs_mount_t;
>  
>  /*
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index dab9a5f..e32b309 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -773,8 +773,15 @@ xfs_init_mount_workqueues(
>  	if (!mp->m_unwritten_workqueue)
>  		goto out_destroy_data_iodone_queue;
>  
> +	mp->m_flush_workqueue = alloc_workqueue("xfs-flush/%s",
> +			WQ_MEM_RECLAIM, 0, mp->m_fsname);
> +	if (!mp->m_flush_workqueue)
> +		goto out_destroy_unwritten_queue;
> +
>  	return 0;
>  
> +out_destroy_unwritten_queue:
> +	destroy_workqueue(mp->m_unwritten_workqueue);
>  out_destroy_data_iodone_queue:
>  	destroy_workqueue(mp->m_data_workqueue);
>  out:
> @@ -785,6 +792,7 @@ STATIC void
>  xfs_destroy_mount_workqueues(
>  	struct xfs_mount	*mp)
>  {
> +	destroy_workqueue(mp->m_flush_workqueue);
>  	destroy_workqueue(mp->m_data_workqueue);
>  	destroy_workqueue(mp->m_unwritten_workqueue);
>  }

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