mm/ksm.c: mark stable page dirty

The MADV_FREE patchset changes page reclaim to simply free a clean
anonymous page with no dirty ptes, instead of swapping it out; but KSM
uses clean write-protected ptes to reference the stable ksm page.  So be
sure to mark that page dirty, so it's never mistakenly discarded.

[[email protected]: adjusted comments]
Signed-off-by: Minchan Kim <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Chen Gang <[email protected]>
Cc: Chris Zankel <[email protected]>
Cc: Daniel Micay <[email protected]>
Cc: Darrick J. Wong <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Jason Evans <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Matt Turner <[email protected]>
Cc: Max Filippov <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mika Penttil <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Roland Dreier <[email protected]>
Cc: Russell King <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Wu Fengguang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/ksm.c b/mm/ksm.c
index 80c29b1b2b8af3b631dfb30954794560394f1af0..ca6d2a06a6157fabdc01aafa06b797320364a87c 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1013,6 +1013,12 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
                         */
                        set_page_stable_node(page, NULL);
                        mark_page_accessed(page);
+                       /*
+                        * Page reclaim just frees a clean page with no dirty
+                        * ptes: make sure that the ksm page would be swapped.
+                        */
+                       if (!PageDirty(page))
+                               SetPageDirty(page);
                        err = 0;
                } else if (pages_identical(page, kpage))
                        err = replace_page(vma, page, kpage, orig_pte);