linux-kernel - [PATCH v2 0/3] mm/ksm: Fix incorrect accounting of KSM counters during fork.

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Message-ID: <cover.1757946863.git.donettom@linux.ibm.com>
Date: Mon, 15 Sep 2025 20:33:03 +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,
        Giorgi Tchankvetadze <giorgitchankvetadze1997@...il.com>,
        Donet Tom <donettom@...ux.ibm.com>
Subject: [PATCH v2 0/3] mm/ksm: Fix incorrect accounting of KSM counters during fork.

The first patch in this series fixes the incorrect accounting of KSM
counters such as ksm_merging_pages, ksm_rmap_items, and the global
ksm_zero_pages during fork.

The following two patches add selftests to verify that the
ksm_merging_pages counter and the global ksm_zero_pages counter are
updated correctly during fork.

Test Results
============
Without the first patch
-----------------------
# [RUN] test_fork_ksm_merging_page_count
not ok 10 ksm_merging_page in child: 32
# [RUN] test_fork_global_ksm_zero_pages_count
not ok 11 Incorrect global ksm zero page counter after fork

With the first patch
--------------------
# [RUN] test_fork_ksm_merging_page_count
ok 10 ksm_merging_pages is not inherited after fork
# [RUN] test_fork_global_ksm_zero_pages_count
ok 11 Global ksm zero page count is correct after fork

Changes:

v1 -> v2 :
 - Rebased to mm-new branch
 - Fixed incorrect global ksm_zero_pages counter issue during fork and
 added a selftest to verify it.

v1: https://lore.kernel.org/all/2e662107e01417bf9af23bc7f52863cd538419be.1756211338.git.donettom@linux.ibm.com/


Donet Tom (3):
  mm/ksm: Fix incorrect KSM counter handling in mm_struct during fork
  selftests/mm: Added fork inheritance test for ksm_merging_pages
    counter
  selftests/mm: Added fork test to verify global ksm_zero_pages counter
    behavior

 include/linux/ksm.h                           |   8 +-
 .../selftests/mm/ksm_functional_tests.c       | 114 +++++++++++++++++-
 2 files changed, 120 insertions(+), 2 deletions(-)

-- 
2.51.0