3 files changed, 32 insertions, 0 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 62da2001d55c..72be23b1480a 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -125,6 +125,7 @@ static inline void anon_vma_merge(struct vm_area_struct *vma,
 /*
  * rmap interfaces called when adding or removing pte of page
  */
+void page_move_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
 void page_add_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
 void page_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned long);
 void page_add_file_rmap(struct page *);
diff --git a/mm/memory.c b/mm/memory.c
index dc785b438d70..d1153e37e9ba 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2138,6 +2138,13 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
                         page_cache_release(old_page);
                 }
                 reuse = reuse_swap_page(old_page);
+                if (reuse)
+                        /*
+                         * The page is all ours.  Move it to our anon_vma so
+                         * the rmap code will not search our parent or siblings.
+                         * Protected against the rmap code by the page lock.
+                         */
+                        page_move_anon_rmap(old_page, vma, address);
                 unlock_page(old_page);
         } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
                                         (VM_WRITE|VM_SHARED))) {
diff --git a/mm/rmap.c b/mm/rmap.c
index 23ecd0a892df..28bcdc433d88 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -716,6 +716,30 @@ int page_mkclean(struct page *page)
 EXPORT_SYMBOL_GPL(page_mkclean);
 
 /**
+ * page_move_anon_rmap - move a page to our anon_vma
+ * @page:       the page to move to our anon_vma
+ * @vma:        the vma the page belongs to
+ * @address:    the user virtual address mapped
+ *
+ * When a page belongs exclusively to one process after a COW event,
+ * that page can be moved into the anon_vma that belongs to just that
+ * process, so the rmap code will not search the parent or sibling
+ * processes.
+ */
+void page_move_anon_rmap(struct page *page,
+        struct vm_area_struct *vma, unsigned long address)
+{
+        struct anon_vma *anon_vma = vma->anon_vma;
+
+        VM_BUG_ON(!PageLocked(page));
+        VM_BUG_ON(!anon_vma);
+        VM_BUG_ON(page->index != linear_page_index(vma, address));
+
+        anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
+        page->mapping = (struct address_space *) anon_vma;
+}
+
+/**
  * __page_set_anon_rmap - setup new anonymous rmap
  * @page:       the page to add the mapping to
  * @vma:        the vm area in which the mapping is added