1 files changed, 16 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 24c395694f4d..1202cd3121e1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -620,13 +620,22 @@ void page_address_init(void);
 /*
  * On an anonymous page mapped into a user virtual memory area,
  * page->mapping points to its anon_vma, not to a struct address_space;
- * with the PAGE_MAPPING_ANON bit set to distinguish it.
+ * with the PAGE_MAPPING_ANON bit set to distinguish it.  See rmap.h.
+ *
+ * On an anonymous page in a VM_MERGEABLE area, if CONFIG_KSM is enabled,
+ * the PAGE_MAPPING_KSM bit may be set along with the PAGE_MAPPING_ANON bit;
+ * and then page->mapping points, not to an anon_vma, but to a private
+ * structure which KSM associates with that merged page.  See ksm.h.
+ *
+ * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is currently never used.
  *
  * Please note that, confusingly, "page_mapping" refers to the inode
  * address_space which maps the page from disk; whereas "page_mapped"
  * refers to user virtual address space into which the page is mapped.
  */
 #define PAGE_MAPPING_ANON       1
+#define PAGE_MAPPING_KSM        2
+#define PAGE_MAPPING_FLAGS      (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM)
 
 extern struct address_space swapper_space;
 static inline struct address_space *page_mapping(struct page *page)
@@ -644,6 +653,12 @@ static inline struct address_space *page_mapping(struct page *page)
         return mapping;
 }
 
+/* Neutral page->mapping pointer to address_space or anon_vma or other */
+static inline void *page_rmapping(struct page *page)
+{
+        return (void *)((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);
+}
+
 static inline int PageAnon(struct page *page)
 {
         return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;