Commit e5677f05 authored by Uros Bizjak's avatar Uros Bizjak Committed by David Sterba
Browse files

btrfs: use atomic_try_cmpxchg in free_extent_buffer 



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.

Reviewed-by: default avatarBoris Burkov <boris@bur.io>
Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent fc65bb53

fs/btrfs/extent_io.c

+2 −4
Original line number Diff line number Diff line
@@ -6362,18 +6362,16 @@ static int release_extent_buffer(struct extent_buffer *eb) 
void free_extent_buffer(struct extent_buffer *eb)

{

	int refs;

	int old;

	if (!eb)

		return;



	while (1) {

	refs = atomic_read(&eb->refs);

	while (1) {

		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;

	}