The patch titled
Subject: mm/page_alloc: use try_cmpxchg in set_pfnblock_flags_mask
has been added to the -mm mm-unstable branch. Its filename is
mm-page_alloc-use-try_cmpxchg-in-set_pfnblock_flags_mask.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-use-try_cmpxchg-in-set_pfnblock_flags_mask.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: mm/page_alloc: use try_cmpxchg in set_pfnblock_flags_mask
Date: Fri, 8 Jul 2022 16:07:36 +0200
Use try_cmpxchg instead of cmpxchg in set_pfnblock_flags_mask. x86
CMPXCHG instruction returns success in ZF flag, so this change saves a
compare after cmpxchg (and related move instruction in front of cmpxchg).
The main loop improves from:
1c5d: 48 89 c2 mov %rax,%rdx
1c60: 48 89 c1 mov %rax,%rcx
1c63: 48 21 fa and %rdi,%rdx
1c66: 4c 09 c2 or %r8,%rdx
1c69: f0 48 0f b1 16 lock cmpxchg %rdx,(%rsi)
1c6e: 48 39 c1 cmp %rax,%rcx
1c71: 75 ea jne 1c5d <...>
to:
1c60: 48 89 ca mov %rcx,%rdx
1c63: 48 21 c2 and %rax,%rdx
1c66: 4c 09 c2 or %r8,%rdx
1c69: f0 48 0f b1 16 lock cmpxchg %rdx,(%rsi)
1c6e: 75 f0 jne 1c60 <...>
Link: https://lkml.kernel.org/r/20220708140736.8737-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-use-try_cmpxchg-in-set_pfnblock_flags_mask
+++ a/mm/page_alloc.c
@@ -602,7 +602,7 @@ void set_pfnblock_flags_mask(struct page
{
unsigned long *bitmap;
unsigned long bitidx, word_bitidx;
- unsigned long old_word, word;
+ unsigned long word;
BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));
@@ -618,12 +618,8 @@ void set_pfnblock_flags_mask(struct page
flags <<= bitidx;
word = READ_ONCE(bitmap[word_bitidx]);
- for (;;) {
- old_word = cmpxchg(&bitmap[word_bitidx], word, (word & ~mask) | flags);
- if (word == old_word)
- break;
- word = old_word;
- }
+ do {
+ } while (!try_cmpxchg(&bitmap[word_bitidx], &word, (word & ~mask) | flags));
}
void set_pageblock_migratetype(struct page *page, int migratetype)
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
mm-page_alloc-use-try_cmpxchg-in-set_pfnblock_flags_mask.patch
compiler-gcch-remove-ancient-workaround-for-gcc-pr-58670.patch
