Commit f0849ac0 authored Apr 05, 2018 by Yang Shi Committed by Linus Torvalds Apr 05, 2018

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@linux.alibaba.com


Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Reported-by: Gang Deng <gavin.dg@linux.alibaba.com>
Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c9e97a19

mm/page_idle.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -65,11 +65,15 @@ static bool page_idle_clear_pte_refs_one(struct page *page,
		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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