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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 <ubizjak@gmail.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2022-10-18 16:51:54 +02:00 committed by Andrew Morton
parent 9fb6beea79
commit 70ec04f348
1 changed files with 5 additions and 8 deletions
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13
drivers/block/zram/zram_drv.c
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@ -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,