From e5677f056010298d3a8d43f710f8b445dd73462d Mon Sep 17 00:00:00 2001
From: Uros Bizjak <ubizjak@gmail.com>
Date: Tue, 9 Aug 2022 18:36:33 +0200
Subject: [PATCH] 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: Boris Burkov <boris@bur.io>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.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 cf4f19e80e2f7..63decf3abe26b 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -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;
+ 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;
}