Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] fs/ext4: Use try_cmpxchg in ext4_update_bh_state | Date | Tue, 9 Aug 2022 18:46:26 +0200 |
| |
Use `!try_cmpxchg(ptr, &old, new)` instead of `cmpxchg(ptr, old, new) != old` in ext4_update_bh_state. This has two benefits:
- The x86 cmpxchg instruction returns success in the ZF flag, so this change saves a compare after cmpxchg, as well as a related move instruction in the front of cmpxchg.
- atomic_try_cmpxchg implicitly assigns the *ptr value to &old when cmpxchg fails, enabling further code simplifications.
This patch has no functional change.
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 601214453c3a..ce2f03621be8 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, -- 2.37.1
| |