Re: [PATCH v3 3/9] xfs: make xfs_bmapi_convert_delalloc() to allocate the target offset

[Darrick J. Wong]

On Tue, Mar 19, 2024 at 09:10:56AM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> Since xfs_bmapi_convert_delalloc() only attempts to allocate the entire
> delalloc extent and require multiple invocations to allocate the target
> offset. So xfs_convert_blocks() add a loop to do this job and we call it
> in the write back path, but xfs_convert_blocks() isn't a common helper.
> Let's do it in xfs_bmapi_convert_delalloc() and drop
> xfs_convert_blocks(), preparing for the post EOF delalloc blocks
> converting in the buffered write begin path.
> 
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  fs/xfs/libxfs/xfs_bmap.c | 34 +++++++++++++++++++++++--
>  fs/xfs/xfs_aops.c        | 54 +++++++++++-----------------------------
>  2 files changed, 46 insertions(+), 42 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 07dc35de8ce5..042e8d3ab0ba 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -4516,8 +4516,8 @@ xfs_bmapi_write(
>   * invocations to allocate the target offset if a large enough physical extent
>   * is not available.
>   */
> -int
> -xfs_bmapi_convert_delalloc(
> +static int

static inline?

> +__xfs_bmapi_convert_delalloc(

Double underscore prefixes read to me like "do this without grabbing
a lock or a resource", not just one step in a loop.

Would you mind changing it to xfs_bmapi_convert_one_delalloc() ?
Then the callsite looks like:

xfs_bmapi_convert_delalloc(...)
{
	...
	do {
		error = xfs_bmapi_convert_one_delalloc(ip, whichfork, offset,
					iomap, seq);
		if (error)
			return error;
	} while (iomap->offset + iomap->length <= offset);
}

With that renamed,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>

--D

>  	struct xfs_inode	*ip,
>  	int			whichfork,
>  	xfs_off_t		offset,
> @@ -4648,6 +4648,36 @@ xfs_bmapi_convert_delalloc(
>  	return error;
>  }
>  
> +/*
> + * Pass in a dellalloc extent and convert it to real extents, return the real
> + * extent that maps offset_fsb in iomap.
> + */
> +int
> +xfs_bmapi_convert_delalloc(
> +	struct xfs_inode	*ip,
> +	int			whichfork,
> +	loff_t			offset,
> +	struct iomap		*iomap,
> +	unsigned int		*seq)
> +{
> +	int			error;
> +
> +	/*
> +	 * Attempt to allocate whatever delalloc extent currently backs offset
> +	 * and put the result into iomap.  Allocate in a loop because it may
> +	 * take several attempts to allocate real blocks for a contiguous
> +	 * delalloc extent if free space is sufficiently fragmented.
> +	 */
> +	do {
> +		error = __xfs_bmapi_convert_delalloc(ip, whichfork, offset,
> +					iomap, seq);
> +		if (error)
> +			return error;
> +	} while (iomap->offset + iomap->length <= offset);
> +
> +	return 0;
> +}
> +
>  int
>  xfs_bmapi_remap(
>  	struct xfs_trans	*tp,
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 813f85156b0c..6479e0dac69d 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -233,45 +233,6 @@ xfs_imap_valid(
>  	return true;
>  }
>  
> -/*
> - * Pass in a dellalloc extent and convert it to real extents, return the real
> - * extent that maps offset_fsb in wpc->iomap.
> - *
> - * The current page is held locked so nothing could have removed the block
> - * backing offset_fsb, although it could have moved from the COW to the data
> - * fork by another thread.
> - */
> -static int
> -xfs_convert_blocks(
> -	struct iomap_writepage_ctx *wpc,
> -	struct xfs_inode	*ip,
> -	int			whichfork,
> -	loff_t			offset)
> -{
> -	int			error;
> -	unsigned		*seq;
> -
> -	if (whichfork == XFS_COW_FORK)
> -		seq = &XFS_WPC(wpc)->cow_seq;
> -	else
> -		seq = &XFS_WPC(wpc)->data_seq;
> -
> -	/*
> -	 * Attempt to allocate whatever delalloc extent currently backs offset
> -	 * and put the result into wpc->iomap.  Allocate in a loop because it
> -	 * may take several attempts to allocate real blocks for a contiguous
> -	 * delalloc extent if free space is sufficiently fragmented.
> -	 */
> -	do {
> -		error = xfs_bmapi_convert_delalloc(ip, whichfork, offset,
> -				&wpc->iomap, seq);
> -		if (error)
> -			return error;
> -	} while (wpc->iomap.offset + wpc->iomap.length <= offset);
> -
> -	return 0;
> -}
> -
>  static int
>  xfs_map_blocks(
>  	struct iomap_writepage_ctx *wpc,
> @@ -289,6 +250,7 @@ xfs_map_blocks(
>  	struct xfs_iext_cursor	icur;
>  	int			retries = 0;
>  	int			error = 0;
> +	unsigned int		*seq;
>  
>  	if (xfs_is_shutdown(mp))
>  		return -EIO;
> @@ -386,7 +348,19 @@ xfs_map_blocks(
>  	trace_xfs_map_blocks_found(ip, offset, count, whichfork, &imap);
>  	return 0;
>  allocate_blocks:
> -	error = xfs_convert_blocks(wpc, ip, whichfork, offset);
> +	/*
> +	 * Convert a dellalloc extent to a real one. The current page is held
> +	 * locked so nothing could have removed the block backing offset_fsb,
> +	 * although it could have moved from the COW to the data fork by another
> +	 * thread.
> +	 */
> +	if (whichfork == XFS_COW_FORK)
> +		seq = &XFS_WPC(wpc)->cow_seq;
> +	else
> +		seq = &XFS_WPC(wpc)->data_seq;
> +
> +	error = xfs_bmapi_convert_delalloc(ip, whichfork, offset,
> +				&wpc->iomap, seq);
>  	if (error) {
>  		/*
>  		 * If we failed to find the extent in the COW fork we might have
> -- 
> 2.39.2
> 
>