Commit 70ec04f3 authored by Uros Bizjak's avatar Uros Bizjak Committed by Andrew Morton
Browse files

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: default avatarUros Bizjak <ubizjak@gmail.com>
Reviewed-by: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 9fb6beea

drivers/block/zram/zram_drv.c

+5 −8
Original line number Diff line number Diff line
@@ -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,