[V3] iomap: skip unnecessary ifs_block_is_uptodate check

Commit Message

Gou Hao April 10, 2025, 7:12 a.m. UTC

In iomap_adjust_read_range, i is either the first !uptodate block, or it
is past last for the second loop looking for trailing uptodate blocks.
Assuming there's no overflow (there's no combination of huge folios and
tiny blksize) then yeah, there is no point in retesting that the same
block pointed to by i is uptodate since we hold the folio lock so nobody
else could have set it uptodate.

Signed-off-by: Gou Hao <[e-mail]>
Reviewed-by: "Darrick J. Wong" <[e-mail]>
Suggested-by: Christoph Hellwig <[e-mail]>
---
 fs/iomap/buffered-io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Changes:
V3:
- optimize commit log
- change 'for' to 'while'

V2:
- optimize commit log

Comments

Christoph Hellwig April 10, 2025, 7:17 a.m. UTC | #1

Looks good:

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

Christian Brauner April 11, 2025, 2:02 p.m. UTC | #2

On Thu, 10 Apr 2025 15:12:36 +0800, Gou Hao wrote:
> In iomap_adjust_read_range, i is either the first !uptodate block, or it
> is past last for the second loop looking for trailing uptodate blocks.
> Assuming there's no overflow (there's no combination of huge folios and
> tiny blksize) then yeah, there is no point in retesting that the same
> block pointed to by i is uptodate since we hold the folio lock so nobody
> else could have set it uptodate.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] iomap: skip unnecessary ifs_block_is_uptodate check
      https://git.kernel.org/vfs/vfs/c/8e3c15ee0d29

Patch

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 31553372b33a..5b08bd417b28 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -259,7 +259,7 @@  static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
 		}
 
 		/* truncate len if we find any trailing uptodate block(s) */
-		for ( ; i <= last; i++) {
+		while (++i <= last) {
 			if (ifs_block_is_uptodate(ifs, i)) {
 				plen -= (last - i + 1) * block_size;
 				last = i - 1;