linux-kernel - [PATCH v3 0/2] mm/ksm: Fix incorrect accounting of KSM counters during fork.

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Message-ID: <cover.1758648700.git.donettom@linux.ibm.com>
Date: Wed, 24 Sep 2025 00:16:58 +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 v3 0/2] 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 patch added a selftest to verify the ksm_merging_pages
counter was 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

With the first patch
--------------------
 # [RUN] test_fork_ksm_merging_page_count
 ok 10 ksm_merging_pages is not inherited after fork

Changes:
V2 -> v3:
- Added Reviewed-by and Acked-by tags
- Added cleanup on exit in ksm_merging_pages test.
- Dropped test_fork_global_ksm_zero_pages_count because it can give false
  failures if multiple processes attempt KSM zero-page merging and unmerging
  during test execution.

v2: https://lore.kernel.org/all/cover.1757946863.git.donettom@linux.ibm.com/#t

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

Donet Tom (2):
  mm/ksm: Fix incorrect KSM counter handling in mm_struct during fork
  selftests/mm: Added fork inheritance test for ksm_merging_pages
    counter

 include/linux/ksm.h                           |  8 +++-
 .../selftests/mm/ksm_functional_tests.c       | 43 ++++++++++++++++++-
 2 files changed, 49 insertions(+), 2 deletions(-)

-- 
2.51.0