Messages in this thread | | | Date | Mon, 15 Aug 2022 14:36:25 -0700 | From | Boris Burkov <> | Subject | Re: [PATCH] fs/btrfs: Use atomic_try_cmpxchg in free_extent_buffer |
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On Tue, Aug 09, 2022 at 06:36:33PM +0200, Uros Bizjak wrote: > 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> Reviewed-by: Boris Burkov <boris@bur.io> > --- > 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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