Re: [PATCH 17/19] xfs: reorder the minlen and prod calculations in xfs_bmap_rtalloc

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

On Thu, Dec 14, 2023 at 07:34:36AM +0100, Christoph Hellwig wrote:
> xfs_bmap_rtalloc is a bit of a mess in terms of calculating the locally
> need variables.  Reorder them a bit so that related code is located
> next to each other - the raminlen calculation moves up next to where
> the maximum len is calculated, and all the prod calculation is move
> into a single place and rearranged so that the real prod calculation
> only happens when it actually is needed.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

This looks like a simple enough change,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_rtalloc.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
> index 24d74c8b532e5f..595740d18dc4c3 100644
> --- a/fs/xfs/xfs_rtalloc.c
> +++ b/fs/xfs/xfs_rtalloc.c
> @@ -1369,7 +1369,6 @@ xfs_bmap_rtalloc(
>  
>  	align = xfs_get_extsz_hint(ap->ip);
>  retry:
> -	prod = xfs_extlen_to_rtxlen(mp, align);
>  	error = xfs_bmap_extsize_align(mp, &ap->got, &ap->prev,
>  					align, 1, ap->eof, 0,
>  					ap->conv, &ap->offset, &ap->length);
> @@ -1387,13 +1386,6 @@ xfs_bmap_rtalloc(
>  	if (ap->offset != orig_offset)
>  		minlen += orig_offset - ap->offset;
>  
> -	/*
> -	 * If the offset & length are not perfectly aligned
> -	 * then kill prod, it will just get us in trouble.
> -	 */
> -	div_u64_rem(ap->offset, align, &mod);
> -	if (mod || ap->length % align)
> -		prod = 1;
>  	/*
>  	 * Set ralen to be the actual requested length in rtextents.
>  	 *
> @@ -1404,6 +1396,7 @@ xfs_bmap_rtalloc(
>  	 * adjust the starting point to match it.
>  	 */
>  	ralen = xfs_extlen_to_rtxlen(mp, min(ap->length, XFS_MAX_BMBT_EXTLEN));
> +	raminlen = max_t(xfs_rtxlen_t, 1, xfs_extlen_to_rtxlen(mp, minlen));
>  
>  	/*
>  	 * Lock out modifications to both the RT bitmap and summary inodes
> @@ -1432,7 +1425,16 @@ xfs_bmap_rtalloc(
>  		start = 0;
>  	}
>  
> -	raminlen = max_t(xfs_rtxlen_t, 1, xfs_extlen_to_rtxlen(mp, minlen));
> +	/*
> +	 * Only bother calculating a real prod factor if offset & length are
> +	 * perfectly aligned, otherwise it will just get us in trouble.
> +	 */
> +	div_u64_rem(ap->offset, align, &mod);
> +	if (mod || ap->length % align)
> +		prod = 1;
> +	else
> +		prod = xfs_extlen_to_rtxlen(mp, align);
> +
>  	error = xfs_rtallocate_extent(ap->tp, start, raminlen, ralen, &ralen,
>  			ap->wasdel, prod, &rtx);
>  	if (error == -ENOSPC) {
> -- 
> 2.39.2
> 
>