mm, thp: fix leaking mapped pte in __collapse_huge_page_swapin()

Currently, khugepaged does not permit swapin if there are enough young
pages in a THP.  The problem is when a THP does not have enough young
pages, khugepaged leaks mapped ptes.

This patch prohibits leaking mapped ptes.

Link: http://lkml.kernel.org/r/1472820276-7831-1-git-send-email-ebru.akagunduz@gmail.com
Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 62339bf..728d779 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -882,6 +882,11 @@ 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) {
@@ -889,11 +894,6 @@ 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 */