The following commit has been merged into the locking/core branch of tip: Commit-ID: 50fd4d5e6914b60ea6f89c2cbff7a07799414c62 Gitweb: https://git.kernel.org/tip/50fd4d5e6914b60ea6f89c2cbff7a07799414c62 Author: Uros Bizjak <ubizjak@xxxxxxxxx> AuthorDate: Mon, 16 Jan 2023 17:34:46 +01:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Thu, 26 Jan 2023 11:49:39 +01:00 x86/PAT: Use try_cmpxchg() in set_page_memtype() Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in set_page_memtype. 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, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. Note that the value from *ptr should be read using READ_ONCE to prevent the compiler from merging, refetching or reordering the read. No functional change intended. Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Link: https://lore.kernel.org/r/20230116163446.4734-1-ubizjak@xxxxxxxxx --- arch/x86/mm/pat/memtype.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c index fb4b1b5..6d1ba2d 100644 --- a/arch/x86/mm/pat/memtype.c +++ b/arch/x86/mm/pat/memtype.c @@ -159,10 +159,10 @@ static inline void set_page_memtype(struct page *pg, break; } + old_flags = READ_ONCE(pg->flags); do { - old_flags = pg->flags; new_flags = (old_flags & _PGMT_CLEAR_MASK) | memtype_flags; - } while (cmpxchg(&pg->flags, old_flags, new_flags) != old_flags); + } while (!try_cmpxchg(&pg->flags, &old_flags, new_flags)); } #else static inline enum page_cache_mode get_page_memtype(struct page *pg)
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