[PATCH 06/10] xfs: don't free post-EOF blocks on read close

Christoph Hellwig
2024-06-23T05:35:59Z

From: Dave Chinner <dchinner@redhat.com>

When we have a workload that does open/read/close in parallel with other
allocation, the file becomes rapidly fragmented. This is due to close()
calling xfs_file_release() and removing the speculative preallocation
beyond EOF.

Add a check for a writable context to xfs_file_release to skip the
post-EOF block freeing (an the similarly pointless flushing on truncate
down).

Before:

Test 1: sync write fragmentation counts

/mnt/scratch/file.0: 919
/mnt/scratch/file.1: 916
/mnt/scratch/file.2: 919
/mnt/scratch/file.3: 920
/mnt/scratch/file.4: 920
/mnt/scratch/file.5: 921
/mnt/scratch/file.6: 916
/mnt/scratch/file.7: 918

After:

Test 1: sync write fragmentation counts

/mnt/scratch/file.0: 24
/mnt/scratch/file.1: 24
/mnt/scratch/file.2: 11
/mnt/scratch/file.3: 24
/mnt/scratch/file.4: 3
/mnt/scratch/file.5: 24
/mnt/scratch/file.6: 24
/mnt/scratch/file.7: 23

Signed-off-by: Dave Chinner <dchinner@redhat.com>
[darrick: wordsmithing, fix commit message]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
[hch: ported to the new ->release code structure]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/xfs_file.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 0380e0b1d9c6c7..8d70171678fe24 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1228,12 +1228,18 @@ xfs_file_release(
* There is no point in freeing blocks here for open but unlinked files
* as they will be taken care of by the inactivation path soon.
*
+ * When releasing a read-only context, don't flush data or trim post-EOF
+ * blocks. This avoids open/read/close workloads from removing EOF
+ * blocks that other writers depend upon to reduce fragmentation.
+ *
* If we can't get the iolock just skip truncating the blocks past EOF
* because we could deadlock with the mmap_lock otherwise. We'll get
* another chance to drop them once the last reference to the inode is
* dropped, so we'll never leak blocks permanently.
*/
- if (inode->i_nlink && xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
+ if (inode->i_nlink &&
+ (file->f_mode & FMODE_WRITE) &&
+ xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
if (xfs_can_free_eofblocks(ip) &&
!xfs_iflags_test(ip, XFS_IDIRTY_RELEASE)) {
/*
--
2.43.0