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Subject[PATCH] mm, thp: fix leaking mapped pte in __collapse_huge_page_swapin()
Date
Currently, khugepaged does not let swapin, if there is no
enough young pages in a THP. The problem is when a THP does
not have enough young page, khugepaged leaks mapped ptes.

This patch prohibits leaking mapped ptes.

Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
---
mm/khugepaged.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 79c52d0..f401e9d 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -881,6 +881,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
.pmd = pmd,
};

+ /* we only decide to swapin, if there is enough young ptes */
+ if (referenced < HPAGE_PMD_NR/2) {
+ trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
+ return false;
+ }
fe.pte = pte_offset_map(pmd, address);
for (; fe.address < address + HPAGE_PMD_NR*PAGE_SIZE;
fe.pte++, fe.address += PAGE_SIZE) {
@@ -888,11 +893,6 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
if (!is_swap_pte(pteval))
continue;
swapped_in++;
- /* we only decide to swapin, if there is enough young ptes */
- if (referenced < HPAGE_PMD_NR/2) {
- trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
- return false;
- }
ret = do_swap_page(&fe, pteval);

/* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
--
1.9.1
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