2 files changed, 13 insertions, 6 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 3922ffcf3dff..8f471edcb985 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1861,7 +1861,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
                         }
                         page_cache_release(old_page);
                 }
-                reuse = can_share_swap_page(old_page);
+                reuse = reuse_swap_page(old_page);
                 unlock_page(old_page);
         } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
                                         (VM_WRITE|VM_SHARED))) {
@@ -2392,7 +2392,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 
         inc_mm_counter(mm, anon_rss);
         pte = mk_pte(page, vma->vm_page_prot);
-        if (write_access && can_share_swap_page(page)) {
+        if (write_access && reuse_swap_page(page)) {
                 pte = maybe_mkwrite(pte_mkdirty(pte), vma);
                 write_access = 0;
         }
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 214e90b94946..bfd4ee59cb88 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -326,17 +326,24 @@ static inline int page_swapcount(struct page *page)
 }
 
 /*
- * We can use this swap cache entry directly
- * if there are no other references to it.
+ * We can write to an anon page without COW if there are no other references
+ * to it.  And as a side-effect, free up its swap: because the old content
+ * on disk will never be read, and seeking back there to write new content
+ * later would only waste time away from clustering.
  */
-int can_share_swap_page(struct page *page)
+int reuse_swap_page(struct page *page)
 {
         int count;
 
         VM_BUG_ON(!PageLocked(page));
         count = page_mapcount(page);
-        if (count <= 1 && PageSwapCache(page))
+        if (count <= 1 && PageSwapCache(page)) {
                 count += page_swapcount(page);
+                if (count == 1 && !PageWriteback(page)) {
+                        delete_from_swap_cache(page);
+                        SetPageDirty(page);
+                }
+        }
         return count == 1;
 }