1 files changed, 10 insertions, 1 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index e74112e8e5f4..6c0585b16418 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -22,6 +22,7 @@
 #include <linux/seq_file.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/ksm.h>
 #include <linux/rmap.h>
 #include <linux/security.h>
 #include <linux/backing-dev.h>
@@ -650,6 +651,8 @@ int reuse_swap_page(struct page *page)
         int count;
 
         VM_BUG_ON(!PageLocked(page));
+        if (unlikely(PageKsm(page)))
+                return 0;
         count = page_mapcount(page);
         if (count <= 1 && PageSwapCache(page)) {
                 count += page_swapcount(page);
@@ -658,7 +661,7 @@ int reuse_swap_page(struct page *page)
                         SetPageDirty(page);
                 }
         }
-        return count == 1;
+        return count <= 1;
 }
 
 /*
@@ -1185,6 +1188,12 @@ static int try_to_unuse(unsigned int type)
                  * read from disk into another page.  Splitting into two
                  * pages would be incorrect if swap supported "shared
                  * private" pages, but they are handled by tmpfs files.
+                 *
+                 * Given how unuse_vma() targets one particular offset
+                 * in an anon_vma, once the anon_vma has been determined,
+                 * this splitting happens to be just what is needed to
+                 * handle where KSM pages have been swapped out: re-reading
+                 * is unnecessarily slow, but we can fix that later on.
                  */
                 if (swap_count(*swap_map) &&
                      PageDirty(page) && PageSwapCache(page)) {