Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH RESEND] fs/ext4: Use try_cmpxchg in ext4_update_bh_state | Date | Wed, 2 Nov 2022 08:11:47 +0100 |
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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.
Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Andreas Dilger <adilger.kernel@dilger.ca> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- fs/ext4/inode.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 2b5ef1b64249..162e39e2f59a 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -780,11 +780,10 @@ static void ext4_update_bh_state(struct buffer_head *bh, unsigned long flags) * 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, -- 2.37.3
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