linux-kernel - [PATCH v8 5/6] ksm: update the calculation of KSM profit

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Date:   Mon, 22 May 2023 18:54:02 +0800
From:   Yang Yang <yang.yang29@....com.cn>
To:     akpm@...ux-foundation.org, david@...hat.com
Cc:     yang.yang29@....com.cn, imbrenda@...ux.ibm.com,
        jiang.xuexin@....com.cn, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, ran.xiaokai@....com.cn, xu.xin.sc@...il.com,
        xu.xin16@....com.cn
Subject: [PATCH v8 5/6] ksm: update the calculation of KSM profit

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

When use_zero_pages is enabled, the calculation of ksm profit is not
correct because ksm zero pages is not counted in. So update the
calculation of KSM profit including the documentation.

Signed-off-by: xu xin <xu.xin16@....com.cn>
Cc: Xiaokai Ran <ran.xiaokai@....com.cn>
Cc: Yang Yang <yang.yang29@....com.cn>
Cc: Jiang Xuexin <jiang.xuexin@....com.cn>
Cc: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: David Hildenbrand <david@...hat.com>
---
 Documentation/admin-guide/mm/ksm.rst | 18 +++++++++++-------
 mm/ksm.c                             |  2 +-
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 019dc40a0d3c..dde7c152f0ae 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -204,21 +204,25 @@ several times, which are unprofitable memory consumed.
 1) How to determine whether KSM save memory or consume memory in system-wide
    range? Here is a simple approximate calculation for reference::
 
-	general_profit =~ pages_sharing * sizeof(page) - (all_rmap_items) *
+	general_profit =~ ksm_saved_pages * sizeof(page) - (all_rmap_items) *
 			  sizeof(rmap_item);
 
-   where all_rmap_items can be easily obtained by summing ``pages_sharing``,
-   ``pages_shared``, ``pages_unshared`` and ``pages_volatile``.
+   where ksm_saved_pages equals to the sum of ``pages_sharing`` +
+   ``ksm_zero_pages`` of the system, and all_rmap_items can be easily
+   obtained by summing ``pages_sharing``, ``pages_shared``, ``pages_unshared``
+   and ``pages_volatile``.
 
 2) The KSM profit inner a single process can be similarly obtained by the
    following approximate calculation::
 
-	process_profit =~ ksm_merging_pages * sizeof(page) -
+	process_profit =~ ksm_saved_pages * sizeof(page) -
 			  ksm_rmap_items * sizeof(rmap_item).
 
-   where ksm_merging_pages is shown under the directory ``/proc/<pid>/``,
-   and ksm_rmap_items is shown in ``/proc/<pid>/ksm_stat``. The process profit
-   is also shown in ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
+   where ksm_saved_pages equals to the sum of ``ksm_merging_pages`` and
+   ``ksm_zero_pages``, both of which are shown under the directory
+   ``/proc/<pid>/ksm_stat``, and ksm_rmap_items is alos shown in
+   ``/proc/<pid>/ksm_stat``. The process profit is also shown in
+   ``/proc/<pid>/ksm_stat`` as ksm_process_profit.
 
 From the perspective of application, a high ratio of ``ksm_rmap_items`` to
 ``ksm_merging_pages`` means a bad madvise-applied policy, so developers or
diff --git a/mm/ksm.c b/mm/ksm.c
index 4e510f5c5938..d23a240c2519 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3085,7 +3085,7 @@ static void wait_while_offlining(void)
 #ifdef CONFIG_PROC_FS
 long ksm_process_profit(struct mm_struct *mm)
 {
-	return mm->ksm_merging_pages * PAGE_SIZE -
+	return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE -
 		mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
 }
 #endif /* CONFIG_PROC_FS */
-- 
2.15.2