[PATCH v8 4/6] ksm: add documentation for ksm zero pages

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

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

Add the description of ksm_zero_pages.

When use_zero_pages is enabled, pages_sharing cannot represent how
much memory saved actually by KSM, but the sum of ksm_zero_pages +
pages_sharing does.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
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>
---
 Documentation/admin-guide/mm/ksm.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 7626392fe82c..019dc40a0d3c 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -173,6 +173,14 @@ stable_node_chains
         the number of KSM pages that hit the ``max_page_sharing`` limit
 stable_node_dups
         number of duplicated KSM pages
+ksm_zero_pages
+        how many empty pages are sharing the kernel zero page(s) instead
+        of other user pages as it would happen normally. Only meaningful
+        when ``use_zero_pages`` is/was enabled.
+
+When ``use_zero_pages`` is/was enabled, the sum of ``pages_sharing`` +
+``ksm_zero_pages`` represents the actual number of pages saved by KSM.
+if ``use_zero_pages`` has never been enabled, ``ksm_zero_pages`` is 0.
 
 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