linux-kernel - [PATCH 1/2] mm/ksm: Reset KSM counters in mm

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Message-ID: <2e662107e01417bf9af23bc7f52863cd538419be.1756211338.git.donettom@linux.ibm.com>
Date: Tue, 26 Aug 2025 18:19:21 +0530
From: Donet Tom <donettom@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>
Cc: Ritesh Harjani <ritesh.list@...il.com>, Xu Xin <xu.xin16@....com.cn>,
        Chengming Zhou <chengming.zhou@...ux.dev>,
        Wei Yang <richard.weiyang@...il.com>,
        Aboorva Devarajan <aboorvad@...ux.ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Donet Tom <donettom@...ux.ibm.com>
Subject: [PATCH 1/2] mm/ksm: Reset KSM counters in mm_struct during fork

Currently, the KSM-related counters in `mm_struct` such as
`ksm_merging_pages`, `ksm_rmap_items`, and `ksm_zero_pages` are
inherited by the child process during fork. This results in
incorrect accounting, since the child has not performed any
KSM page merging.

To fix this, reset these counters to 0 in the newly created
`mm_struct` during fork. This ensures that KSM statistics
remain accurate and only reflect the activity of each process.

Signed-off-by: Donet Tom <donettom@...ux.ibm.com>
---
 include/linux/ksm.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 22e67ca7cba3..61b8892c632b 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -56,8 +56,12 @@ static inline long mm_ksm_zero_pages(struct mm_struct *mm)
 static inline void ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
 	/* Adding mm to ksm is best effort on fork. */
-	if (mm_flags_test(MMF_VM_MERGEABLE, oldmm))
+	if (mm_flags_test(MMF_VM_MERGEABLE, oldmm)) {
+		mm->ksm_merging_pages = 0;
+		mm->ksm_rmap_items = 0;
+		atomic_long_set(&mm->ksm_zero_pages, 0);
 		__ksm_enter(mm);
+	}
 }
 
 static inline int ksm_execve(struct mm_struct *mm)
-- 
2.51.0