The patch titled
Subject: fs/ext4: use try_cmpxchg in ext4_update_bh_state
has been added to the -mm mm-nonmm-unstable branch. Its filename is
fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: fs/ext4: use try_cmpxchg in ext4_update_bh_state
Date: Wed, 2 Nov 2022 08:11:47 +0100
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
ext4_update_bh_state. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move instruction
in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.
No functional change intended.
Link: https://lkml.kernel.org/r/20221102071147.6642-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ext4/inode.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- a/fs/ext4/inode.c~fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state
+++ a/fs/ext4/inode.c
@@ -786,11 +786,10 @@ static void ext4_update_bh_state(struct
* once we get rid of using bh as a container for mapping information
* to pass to / from get_block functions, this can go away.
*/
+ old_state = READ_ONCE(bh->b_state);
do {
- old_state = READ_ONCE(bh->b_state);
new_state = (old_state & ~EXT4_MAP_FLAGS) | flags;
- } while (unlikely(
- cmpxchg(&bh->b_state, old_state, new_state) != old_state));
+ } while (unlikely(!try_cmpxchg(&bh->b_state, &old_state, new_state)));
}
static int _ext4_get_block(struct inode *inode, sector_t iblock,
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
lib-genalloc-use-try_cmpxchg-in-setclear_bits_ll.patch
fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch
