[PATCH v2 07/13] mm: mark stable page dirty in KSM

From: Minchan Kim
Date: Tue Nov 03 2015 - 20:26:41 EST

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.

[hughd: adjusted comments]
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
mm/ksm.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/mm/ksm.c b/mm/ksm.c
index 7ee101eaacdf..18d2b7afecff 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1053,6 +1053,12 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
set_page_stable_node(page, NULL);
+ /*
+ * 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);

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