Re: [PATCH 6/6] xfs: don't look for end of extent further than necessary in xfs_rtallocate_extent_near()

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

On Tue, Jun 20, 2023 at 02:32:16PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> As explained in the previous commit, xfs_rtallocate_extent_near() looks
> for the end of a free extent when searching backwards from the target
> bitmap block. Since the previous commit, it searches from the last
> bitmap block it checked to the bitmap block containing the start of the
> extent.
> 
> This may still be more than necessary, since the free extent may not be
> that long. We know the maximum size of the free extent from the realtime
> summary. Use that to compute how many bitmap blocks we actually need to
> check.
> 
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
>  fs/xfs/xfs_rtalloc.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
> index 4d9d0be2e616..2e2eb7c4a648 100644
> --- a/fs/xfs/xfs_rtalloc.c
> +++ b/fs/xfs/xfs_rtalloc.c
> @@ -517,12 +517,29 @@ xfs_rtallocate_extent_near(
>  			 * On the negative side of the starting location.
>  			 */
>  			else {		/* i < 0 */
> +				int maxblocks;
> +
>  				/*
> -				 * Loop backwards through the bitmap blocks from
> -				 * where we last checked up to where we are now.
> -				 * There should be an extent which ends in this
> -				 * bitmap block and is long enough.
> +				 * Loop backwards to find the end of the extent
> +				 * we found in the realtime summary.
> +				 *
> +				 * maxblocks is the maximum possible number of
> +				 * bitmap blocks from the start of the extent to
> +				 * the end of the extent.
>  				 */
> +				if (maxlog == 0)
> +					maxblocks = 0;
> +				else if (maxlog < mp->m_blkbit_log)
> +					maxblocks = 1;
> +				else
> +					maxblocks = 2 << (maxlog - mp->m_blkbit_log);
> +				/*
> +				 * We need to check bbno + i + maxblocks down to
> +				 * bbno + i. We already checked bbno down to
> +				 * bbno + j + 1, so we don't need to check those
> +				 * again.
> +				 */
> +				j = min(i + maxblocks, j);

Makes sense now with a fresher head...
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

What does the xfsprogs version of this patchset look like?

--D

>  				for (; j >= i; j--) {
>  					error = xfs_rtallocate_extent_block(mp,
>  						tp, bbno + j, minlen, maxavail,
> -- 
> 2.41.0
>