Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] fs/btrfs: Use atomic_try_cmpxchg in free_extent_buffer | Date | Tue, 9 Aug 2022 18:36:33 +0200 |
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Use `atomic_try_cmpxchg(ptr, &old, new)` instead of `atomic_cmpxchg(ptr, old, new) == old` in free_extent_buffer. 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: Chris Mason <clm@fb.com> Cc: Josef Bacik <josef@toxicpanda.com> Cc: David Sterba <dsterba@suse.com> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- fs/btrfs/extent_io.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index bfae67c593c5..15ff196cbd6d 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -6328,18 +6328,16 @@ static int release_extent_buffer(struct extent_buffer *eb) void free_extent_buffer(struct extent_buffer *eb) { int refs; - int old; if (!eb) return; + refs = atomic_read(&eb->refs); while (1) { - refs = atomic_read(&eb->refs); if ((!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) && refs <= 3) || (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) && refs == 1)) break; - old = atomic_cmpxchg(&eb->refs, refs, refs - 1); - if (old == refs) + if (atomic_try_cmpxchg(&eb->refs, &refs, refs - 1)) return; } -- 2.37.1
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