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authorUros Bizjak <ubizjak@gmail.com>2022-07-08 16:07:36 +0200
committerakpm <akpm@linux-foundation.org>2022-07-17 17:14:47 -0700
commit04ec006171badc73f749dc1cd9d66e05f8575a81 (patch)
treede870dacd5654ddd7a5795a29ccf6de657a519d9 /mm
parentdcadcf1c30619ead2f3280bfb7f74de8304be2bb (diff)
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mm/page_alloc: use try_cmpxchg in set_pfnblock_flags_mask
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@gmail.com Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/page_alloc.c10
1 files changed, 3 insertions, 7 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4fa96d3510fe..50d96fff8855 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -602,7 +602,7 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
{
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 *page, unsigned long flags,
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)