fs/ext4: Use try_cmpxchg in ext4_update_bh_state
PATCH RESEND 1/1 fs/ext4: Use try_cmpxchg in ext4_update_bh_state
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" <[email protected]>
Cc Andreas Dilger <[email protected]>
Signed-off-by Uros Bizjak <[email protected]>
--- fs/ext4/inode.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
fs/ext4/inode.c +2 -3
@@ -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,
Signature · 1 line
2.37.3