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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.com>,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 19/19] xfs: improve the IOMAP_NOWAIT check for COW inodes
Date: Wed, 18 Sep 2019 11:09:01 -0700
Message-ID: <20190918180901.GL2229799@magnolia> (raw)
In-Reply-To: <20190909182722.16783-20-hch@lst.de>

On Mon, Sep 09, 2019 at 08:27:22PM +0200, Christoph Hellwig wrote:
> Only bail out once we know that a COW allocation is actually required,
> similar to how we handle normal data fork allocations.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

/me is still a little fuzzy about what NOWAIT is actually supposed to
mean (no waiting for fs metadata to load?  no waiting on other io to the
same device?  no waiting for anything, period?) but afaict this doesn't
seem to change the behavior much...

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/xfs_iomap.c | 23 +++++------------------
>  1 file changed, 5 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index e4e79aa5b695..9e1b4b94acac 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -693,15 +693,8 @@ xfs_ilock_for_iomap(
>  	 * COW writes may allocate delalloc space or convert unwritten COW
>  	 * extents, so we need to make sure to take the lock exclusively here.
>  	 */
> -	if (xfs_is_cow_inode(ip) && is_write) {
> -		/*
> -		 * FIXME: It could still overwrite on unshared extents and not
> -		 * need allocation.
> -		 */
> -		if (flags & IOMAP_NOWAIT)
> -			return -EAGAIN;
> +	if (xfs_is_cow_inode(ip) && is_write)
>  		mode = XFS_ILOCK_EXCL;
> -	}
>  
>  	/*
>  	 * Extents not yet cached requires exclusive access, don't block.  This
> @@ -760,12 +753,6 @@ xfs_direct_write_iomap_begin(
>  	if (XFS_FORCED_SHUTDOWN(mp))
>  		return -EIO;
>  
> -	/*
> -	 * Lock the inode in the manner required for the specified operation and
> -	 * check for as many conditions that would result in blocking as
> -	 * possible. This removes most of the non-blocking checks from the
> -	 * mapping code below.
> -	 */
>  	error = xfs_ilock_for_iomap(ip, flags, &lockmode);
>  	if (error)
>  		return error;
> @@ -775,11 +762,11 @@ xfs_direct_write_iomap_begin(
>  	if (error)
>  		goto out_unlock;
>  
> -	/*
> -	 * Break shared extents if necessary. Checks for non-blocking IO have
> -	 * been done up front, so we don't need to do them here.
> -	 */
>  	if (imap_needs_cow(ip, &imap, flags, nimaps)) {
> +		error = -EAGAIN;
> +		if (flags & IOMAP_NOWAIT)
> +			goto out_unlock;
> +
>  		/* may drop and re-acquire the ilock */
>  		error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
>  				&lockmode, flags & IOMAP_DIRECT);
> -- 
> 2.20.1
> 

      reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-09 18:27 iomap and xfs COW cleanups Christoph Hellwig
2019-09-09 18:27 ` [PATCH 01/19] iomap: better document the IOMAP_F_* flags Christoph Hellwig
2019-09-14  0:42   ` Allison Collins
2019-09-16 18:08   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 02/19] iomap: remove the unused iomap argument to __iomap_write_end Christoph Hellwig
2019-09-14  0:42   ` Allison Collins
2019-09-16 18:10   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 03/19] iomap: always use AOP_FLAG_NOFS in iomap_write_begin Christoph Hellwig
2019-09-16 18:11   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 04/19] iomap: ignore non-shared or non-data blocks in xfs_file_dirty Christoph Hellwig
2019-09-16 18:12   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 05/19] iomap: move the zeroing case out of iomap_read_page_sync Christoph Hellwig
2019-09-16 18:17   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 06/19] iomap: use write_begin to read pages to unshare Christoph Hellwig
2019-09-16 18:34   ` Darrick J. Wong
2019-09-30 11:07     ` Christoph Hellwig
2019-10-08 15:12       ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 07/19] iomap: use a srcmap for a read-modify-write I/O Christoph Hellwig
2019-09-10 12:48   ` Goldwyn Rodrigues
2019-09-10 14:39     ` hch
2019-09-16 17:57       ` Darrick J. Wong
2019-09-16 18:42   ` Darrick J. Wong
2019-09-18 18:15     ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 08/19] xfs: also call xfs_file_iomap_end_delalloc for zeroing operations Christoph Hellwig
2019-09-18 17:09   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 09/19] xfs: remove xfs_reflink_dirty_extents Christoph Hellwig
2019-09-18 17:17   ` Darrick J. Wong
2019-09-18 17:25     ` Christoph Hellwig
2019-09-18 17:31       ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 10/19] xfs: pass two imaps to xfs_reflink_allocate_cow Christoph Hellwig
2019-09-18 17:26   ` Darrick J. Wong
2019-09-30 11:10     ` Christoph Hellwig
2019-09-09 18:27 ` [PATCH 11/19] xfs: refactor xfs_file_iomap_begin_delay Christoph Hellwig
2019-09-18 17:30   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 12/19] xfs: fill out the srcmap in iomap_begin Christoph Hellwig
2019-09-18 17:52   ` Darrick J. Wong
2019-10-01  6:26     ` Christoph Hellwig
2019-09-09 18:27 ` [PATCH 13/19] xfs: factor out a helper to calculate the end_fsb Christoph Hellwig
2019-09-14  0:42   ` Allison Collins
2019-09-18 17:55   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 14/19] xfs: split out a new set of read-only iomap ops Christoph Hellwig
2019-09-18 17:56   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 15/19] xfs: move xfs_file_iomap_begin_delay around Christoph Hellwig
2019-09-18 17:59   ` Darrick J. Wong
2019-09-30 11:14     ` Christoph Hellwig
2019-09-09 18:27 ` [PATCH 16/19] xfs: split the iomap ops for buffered vs direct writes Christoph Hellwig
2019-09-18 18:00   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 17/19] xfs: rename the whichfork variable in xfs_buffered_write_iomap_begin Christoph Hellwig
2019-09-14  0:42   ` Allison Collins
2019-09-18 18:00   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 18/19] xfs: cleanup xfs_iomap_write_unwritten Christoph Hellwig
2019-09-18 18:06   ` Darrick J. Wong
2019-09-09 18:27 ` [PATCH 19/19] xfs: improve the IOMAP_NOWAIT check for COW inodes Christoph Hellwig
2019-09-18 18:09   ` Darrick J. Wong [this message]

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