Re: [PATCH 5/8] xfs: pass the actual offset and len to allocate to xfs_bmapi_allocate

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Apr 08, 2024 at 04:54:51PM +0200, Christoph Hellwig wrote:
> xfs_bmapi_allocate currently overwrites offset and len when converting
> delayed allocations, and duplicates the length cap done for non-delalloc
> allocations.  Move all that logic into the callers to avoid duplication
> and to make the calling conventions more obvious.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_bmap.c | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index f2e934c2fb423c..aa182937de4641 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -4194,21 +4194,11 @@ xfs_bmapi_allocate(
>  	int			error;
>  
>  	ASSERT(bma->length > 0);
> +	ASSERT(bma->length <= XFS_MAX_BMBT_EXTLEN);
>  
> -	/*
> -	 * For the wasdelay case, we could also just allocate the stuff asked
> -	 * for in this bmap call but that wouldn't be as good.
> -	 */
>  	if (bma->wasdel) {
> -		bma->length = (xfs_extlen_t)bma->got.br_blockcount;
> -		bma->offset = bma->got.br_startoff;
>  		if (!xfs_iext_peek_prev_extent(ifp, &bma->icur, &bma->prev))
>  			bma->prev.br_startoff = NULLFILEOFF;
> -	} else {
> -		bma->length = XFS_FILBLKS_MIN(bma->length, XFS_MAX_BMBT_EXTLEN);
> -		if (!bma->eof)
> -			bma->length = XFS_FILBLKS_MIN(bma->length,
> -					bma->got.br_startoff - bma->offset);
>  	}
>  
>  	if (bma->flags & XFS_BMAPI_CONTIG)
> @@ -4542,6 +4532,15 @@ xfs_bmapi_write(
>  			 */
>  			bma.length = XFS_FILBLKS_MIN(len, XFS_MAX_BMBT_EXTLEN);
>  
> +			if (wasdelay) {
> +				bma.offset = bma.got.br_startoff;
> +				bma.length = bma.got.br_blockcount;

This read funny since we'd previously set bma.{offset,length} above, but
I guess that preserves the "convert all the delalloc" behavior; and you
turn it off in patch 8, right?

--D

> +			} else {
> +				if (!eof)
> +					bma.length = XFS_FILBLKS_MIN(bma.length,
> +						bma.got.br_startoff - bno);
> +			}
> +
>  			ASSERT(bma.length > 0);
>  			error = xfs_bmapi_allocate(&bma);
>  			if (error) {
> @@ -4694,11 +4693,16 @@ xfs_bmapi_convert_delalloc(
>  	bma.tp = tp;
>  	bma.ip = ip;
>  	bma.wasdel = true;
> -	bma.offset = bma.got.br_startoff;
> -	bma.length = max_t(xfs_filblks_t, bma.got.br_blockcount,
> -			XFS_MAX_BMBT_EXTLEN);
>  	bma.minleft = xfs_bmapi_minleft(tp, ip, whichfork);
>  
> +	/*
> +	 * Always allocate convert from the start of the delalloc extent even if
> +	 * that is outside the passed in range to create large contiguous
> +	 * extents on disk.
> +	 */
> +	bma.offset = bma.got.br_startoff;
> +	bma.length = bma.got.br_blockcount;
> +
>  	/*
>  	 * When we're converting the delalloc reservations backing dirty pages
>  	 * in the page cache, we must be careful about how we create the new
> -- 
> 2.39.2
> 
>