[PATCH v2] mm: update comments for struct page.mapping

[changbin . du]

From: Changbin Du <changbin.du@xxxxxxxxx>

The struct page.mapping can NULL or points to one object of type
address_space, anon_vma or KSM private structure.

Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>
---
v2: add back flag reference.

---
 include/linux/mm_types.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 46f4ecf5..6d4c51a 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -47,8 +47,10 @@ struct page {
 						 * inode address_space, or NULL.
 						 * If page mapped as anonymous
 						 * memory, low bit is set, and
-						 * it points to anon_vma object:
-						 * see PAGE_MAPPING_ANON below.
+						 * it points to anon_vma object
+						 * or KSM private structure. See
+						 * PAGE_MAPPING_ANON and
+						 * PAGE_MAPPING_KSM.
 						 */
 		void *s_mem;			/* slab first object */
 		atomic_t compound_mapcount;	/* first tail page */
-- 
2.7.4