From: Peter Collingbourne <pcc@xxxxxxxxxx> Subject: 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. Link: https://lkml.kernel.org/r/20220120011200.1322836-1-pcc@xxxxxxxxxx Link: https://linux-review.googlesource.com/id/I2e1f5b5b080ac9c4e0eb7f98768dba6fd7821693 Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mmzone.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/mm/mmzone.c~mm-mmzonec-use-try_cmpxchg-in-page_cpupid_xchg_last +++ a/mm/mmzone.c @@ -89,13 +89,14 @@ int page_cpupid_xchg_last(struct page *p 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; } _
