Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
update_used_max. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).
Also, reorder code a bit to remove additional compare and
conditional jump from the assembly code. Together, hese two
changes save 15 bytes from the function when compiled for x86_64.
No functional change intended.
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
drivers/block/zram/zram_drv.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 966aab902d19..87711ddf4b54 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -188,16 +188,13 @@ static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
static inline void update_used_max(struct zram *zram,
const unsigned long pages)
{
- unsigned long old_max, cur_max;
-
- old_max = atomic_long_read(&zram->stats.max_used_pages);
+ unsigned long cur_max = atomic_long_read(&zram->stats.max_used_pages);
do {
- cur_max = old_max;
- if (pages > cur_max)
- old_max = atomic_long_cmpxchg(
- &zram->stats.max_used_pages, cur_max, pages);
- } while (old_max != cur_max);
+ if (cur_max >= pages)
+ return;
+ } while (!atomic_long_try_cmpxchg(&zram->stats.max_used_pages,
+ &cur_max, pages));
}
static inline void zram_fill_page(void *ptr, unsigned long len,
--
2.37.3