[v2,6/6] xfs: don't look for end of extent further than necessary in xfs_rtallocate_extent_near()

Commit Message

Omar Sandoval Sept. 5, 2023, 9:51 p.m. UTC

From: Omar Sandoval <[e-mail]>

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.

Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Omar Sandoval <[e-mail]>
---
 fs/xfs/xfs_rtalloc.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

Comments

Christoph Hellwig Oct. 9, 2023, 10:39 a.m. UTC | #1

On Tue, Sep 05, 2023 at 02:51:57PM -0700, Omar Sandoval wrote:
> +				if (maxlog == 0)
> +					maxblocks = 0;
> +				else if (maxlog < mp->m_blkbit_log)
> +					maxblocks = 1;
> +				else
> +					maxblocks = 2 << (maxlog - mp->m_blkbit_log);

Overly long line here (can be fixed when applying I guess).

Otherwise looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Patch

diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index 7cbf4ff35887..1a38e981acd4 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -521,12 +521,29 @@  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 down 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);
 				for (; j >= i; j--) {
 					error = xfs_rtallocate_extent_block(mp,
 						tp, bbno + j, minlen, maxavail,