From 70ec04f3486103819807b061b50a99f6e1d2bf36 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Tue, 18 Oct 2022 16:51:54 +0200 Subject: [PATCH] zram: use try_cmpxchg in update_used_max 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. Link: https://lkml.kernel.org/r/20221018145154.3699-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak Reviewed-by: Sergey Senozhatsky Cc: Minchan Kim Cc: Nitin Gupta Signed-off-by: Andrew Morton --- 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 966aab9..87711dd 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, -- 2.7.4