The patch titled
Subject: zram: use try_cmpxchg in update_used_max
has been added to the -mm mm-unstable branch. Its filename is
zram-use-try_cmpxchg-in-update_used_max.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-use-try_cmpxchg-in-update_used_max.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: zram: use try_cmpxchg in update_used_max
Date: Tue, 18 Oct 2022 16:51:54 +0200
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@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
--- a/drivers/block/zram/zram_drv.c~zram-use-try_cmpxchg-in-update_used_max
+++ a/drivers/block/zram/zram_drv.c
@@ -193,16 +193,13 @@ static void update_position(u32 *index,
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,
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
zram-use-try_cmpxchg-in-update_used_max.patch
llist-avoid-extra-memory-read-in-llist_add_batch.patch
