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)
|