[PATCH v4 5/6] ksm: add zero_pages_sharing documentation

[<yang.yang29@zte.com.cn>]

From: xu xin <xu.xin16@zte.com.cn>

When enabling use_zero_pages, pages_sharing cannot represent how
much memory saved indeed. zero_pages_sharing + pages_sharing does.
add the description of zero_pages_sharing.

Cc: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: Jiang Xuexin <jiang.xuexin@zte.com.cn>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
---
 Documentation/admin-guide/mm/ksm.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index fb6ba2002a4b..f160f9487a90 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -173,6 +173,13 @@ stable_node_chains
         the number of KSM pages that hit the ``max_page_sharing`` limit
 stable_node_dups
         number of duplicated KSM pages
+zero_pages_sharing
+        how many empty pages are sharing kernel zero page(s) instead of
+        with each other as it would happen normally. Only effective when
+        enabling ``use_zero_pages`` knob.
+
+When enabling ``use_zero_pages``, the sum of ``pages_sharing`` +
+``zero_pages_sharing`` represents how much really saved by KSM.

 A high ratio of ``pages_sharing`` to ``pages_shared`` indicates good
 sharing, but a high ratio of ``pages_unshared`` to ``pages_sharing``
-- 
2.15.2