linux-kernel - [PATCH v3] xfs: fix the entry condition of exact EOF block allocation optimization

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Message-ID: <20241211120304.3244443-1-alexjlzheng@tencent.com>
Date: Wed, 11 Dec 2024 20:03:04 +0800
From: Jinliang Zheng <alexjlzheng@...il.com>
To: dchinner@...hat.com,
	cem@...nel.org
Cc: djwong@...nel.org,
	chandanbabu@...nel.org,
	linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jinliang Zheng <alexjlzheng@...cent.com>,
	Dave Chinner <david@...morbit.com>
Subject: [PATCH v3] xfs: fix the entry condition of exact EOF block allocation optimization

When we call create(), lseek() and write() sequentially, offset != 0
cannot be used as a judgment condition for whether the file already
has extents.

Furthermore, when xfs_bmap_adjacent() has not given a better blkno,
it is not necessary to use exact EOF block allocation.

Suggested-by: Dave Chinner <david@...morbit.com>
Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>
---
Changelog:
- V3: use ap->eof to mark whether to use the EXACT allocation algorithm
- V2: https://lore.kernel.org/linux-xfs/Z1I74KeyZRv2pBBT@dread.disaster.area/
- V1: https://lore.kernel.org/linux-xfs/ZyFJm7xg7Msd6eVr@dread.disaster.area/T/#t
---
 fs/xfs/libxfs/xfs_bmap.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 5255f93bae31..2b95279303d3 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -3566,12 +3566,12 @@ xfs_bmap_btalloc_at_eof(
 	int			error;
 
 	/*
-	 * If there are already extents in the file, try an exact EOF block
-	 * allocation to extend the file as a contiguous extent. If that fails,
-	 * or it's the first allocation in a file, just try for a stripe aligned
-	 * allocation.
+	 * If there are already extents in the file, and xfs_bmap_adjacent() has
+	 * given a better blkno, try an exact EOF block allocation to extend the
+	 * file as a contiguous extent. If that fails, or it's the first
+	 * allocation in a file, just try for a stripe aligned allocation.
 	 */
-	if (ap->offset) {
+	if (ap->eof) {
 		xfs_extlen_t	nextminlen = 0;
 
 		/*
@@ -3739,7 +3739,8 @@ xfs_bmap_btalloc_best_length(
 	int			error;
 
 	ap->blkno = XFS_INO_TO_FSB(args->mp, ap->ip->i_ino);
-	xfs_bmap_adjacent(ap);
+	if (!xfs_bmap_adjacent(ap))
+		ap->eof = false;
 
 	/*
 	 * Search for an allocation group with a single extent large enough for
-- 
2.41.1