3 files changed, 49 insertions, 4 deletions

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 161e8164abcf..e48b1e453ff5 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -53,6 +53,8 @@ struct page *ksm_might_need_to_copy(struct page *page,
 
 void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc);
 void ksm_migrate_page(struct page *newpage, struct page *oldpage);
+bool reuse_ksm_page(struct page *page,
+                        struct vm_area_struct *vma, unsigned long address);
 
 #else  /* !CONFIG_KSM */
 
@@ -86,6 +88,11 @@ static inline void rmap_walk_ksm(struct page *page,
 static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
 {
 }
+static inline bool reuse_ksm_page(struct page *page,
+                        struct vm_area_struct *vma, unsigned long address)
+{
+        return false;
+}
 #endif /* CONFIG_MMU */
 #endif /* !CONFIG_KSM */
 
diff --git a/mm/ksm.c b/mm/ksm.c
index fd2db6a74d3c..983fbac24bda 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -706,8 +706,9 @@ again:
          * case this node is no longer referenced, and should be freed;
          * however, it might mean that the page is under page_ref_freeze().
          * The __remove_mapping() case is easy, again the node is now stale;
-         * but if page is swapcache in migrate_page_move_mapping(), it might
-         * still be our page, in which case it's essential to keep the node.
+         * the same is in reuse_ksm_page() case; but if page is swapcache
+         * in migrate_page_move_mapping(), it might still be our page,
+         * in which case it's essential to keep the node.
          */
         while (!get_page_unless_zero(page)) {
                 /*
@@ -2642,6 +2643,31 @@ again:
                 goto again;
 }
 
+bool reuse_ksm_page(struct page *page,
+                    struct vm_area_struct *vma,
+                    unsigned long address)
+{
+#ifdef CONFIG_DEBUG_VM
+        if (WARN_ON(is_zero_pfn(page_to_pfn(page))) ||
+                        WARN_ON(!page_mapped(page)) ||
+                        WARN_ON(!PageLocked(page))) {
+                dump_page(page, "reuse_ksm_page");
+                return false;
+        }
+#endif
+
+        if (PageSwapCache(page) || !page_stable_node(page))
+                return false;
+        /* Prohibit parallel get_ksm_page() */
+        if (!page_ref_freeze(page, 1))
+                return false;
+
+        page_move_anon_rmap(page, vma);
+        page->index = linear_page_index(vma, address);
+        page_ref_unfreeze(page, 1);
+
+        return true;
+}
 #ifdef CONFIG_MIGRATION
 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
 {
diff --git a/mm/memory.c b/mm/memory.c
index eb40f32295d2..222da66f16b4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2505,8 +2505,11 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
          * Take out anonymous pages first, anonymous shared vmas are
          * not dirty accountable.
          */
-        if (PageAnon(vmf->page) && !PageKsm(vmf->page)) {
+        if (PageAnon(vmf->page)) {
                 int total_map_swapcount;
+                if (PageKsm(vmf->page) && (PageSwapCache(vmf->page) ||
+                                           page_count(vmf->page) != 1))
+                        goto copy;
                 if (!trylock_page(vmf->page)) {
                         get_page(vmf->page);
                         pte_unmap_unlock(vmf->pte, vmf->ptl);
@@ -2521,6 +2524,15 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
                         }
                         put_page(vmf->page);
                 }
+                if (PageKsm(vmf->page)) {
+                        bool reused = reuse_ksm_page(vmf->page, vmf->vma,
+                                                     vmf->address);
+                        unlock_page(vmf->page);
+                        if (!reused)
+                                goto copy;
+                        wp_page_reuse(vmf);
+                        return VM_FAULT_WRITE;
+                }
                 if (reuse_swap_page(vmf->page, &total_map_swapcount)) {
                         if (total_map_swapcount == 1) {
                                 /*
@@ -2541,7 +2553,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
                                         (VM_WRITE|VM_SHARED))) {
                 return wp_page_shared(vmf);
         }
-
+copy:
         /*
          * Ok, we need to copy. Oh, well..
          */