mm/mmzone.c: use try_cmpxchg() in page_cpupid_xchg_last()

PATCH Applied Peter Collingbourne 1 participant 1 message Jan 20, 2022

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Memory management MM core

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Peter Collingbourne

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2022-01-20 01:12 UTC #0 lore raw

PATCH v2 1/1 mm/mmzone.c: use try_cmpxchg() in page_cpupid_xchg_last()

This will let us avoid an additional read from page->flags when retrying the compare-exchange on some architectures.

Signed-off-by Peter Collingbourne <[email protected]>

Link https://linux-review.googlesource.com/id/I2e1f5b5b080ac9c4e0eb7f98768dba6fd7821693

---
 mm/mmzone.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

mm/mmzone.c +4 -3

index eb89d6e018e2..d8a9b0e1b526 100644
@@ -89,13 +89,14 @@ int page_cpupid_xchg_last(struct page *page, int cpupid)
 	unsigned long old_flags, flags;
 	int last_cpupid;
 
+	old_flags = READ_ONCE(page->flags);
 	do {
-		old_flags = flags = page->flags;
-		last_cpupid = page_cpupid_last(page);
+		flags = old_flags;
+		last_cpupid = (flags >> LAST_CPUPID_PGSHIFT) & LAST_CPUPID_MASK;
 
 		flags &= ~(LAST_CPUPID_MASK << LAST_CPUPID_PGSHIFT);
 		flags |= (cpupid & LAST_CPUPID_MASK) << LAST_CPUPID_PGSHIFT;
-	} while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));
+	} while (unlikely(!try_cmpxchg(&page->flags, &old_flags, flags)));
 
 	return last_cpupid;
 }

Signature · 1 line

2.34.1.703.g22d0c6ccf7-goog