From: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Subject: mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one()
For PTE-mapped THP, the compound THP has not been split to normal 4K pages
yet, the whole THP is considered referenced if any one of sub page is
referenced.
When walking PTE-mapped THP by pvmw, all relevant PTEs will be checked to
retrieve referenced bit. But, the current code just returns the result of
the last PTE. If the last PTE has not referenced, the referenced flag
will be cleared.
Just set referenced when ptep{pmdp}_clear_young_notify() returns true.
Link: http://lkml.kernel.org/r/1518212451-87134-1-git-send-email-yang.shi@xxxxxxxxxxxxxxxxx
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Reported-by: Gang Deng <gavin.dg@xxxxxxxxxxxxxxxxx>
Suggested-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_idle.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff -puN mm/page_idle.c~mm-thp-fix-potential-clearing-to-referenced-flag-in-page_idle_clear_pte_refs_one mm/page_idle.c
--- a/mm/page_idle.c~mm-thp-fix-potential-clearing-to-referenced-flag-in-page_idle_clear_pte_refs_one
+++ a/mm/page_idle.c
@@ -65,11 +65,15 @@ static bool page_idle_clear_pte_refs_one
while (page_vma_mapped_walk(&pvmw)) {
addr = pvmw.address;
if (pvmw.pte) {
- referenced = ptep_clear_young_notify(vma, addr,
- pvmw.pte);
+ /*
+ * For PTE-mapped THP, one sub page is referenced,
+ * the whole THP is referenced.
+ */
+ if (ptep_clear_young_notify(vma, addr, pvmw.pte))
+ referenced = true;
} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
- referenced = pmdp_clear_young_notify(vma, addr,
- pvmw.pmd);
+ if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
+ referenced = true;
} else {
/* unexpected pmd-mapped page? */
WARN_ON_ONCE(1);
_
--
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