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Mon, 15 Sep 2025 15:03:25 GMT Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D841E20043; Mon, 15 Sep 2025 15:03:24 +0000 (GMT) Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0371A20040; Mon, 15 Sep 2025 15:03:22 +0000 (GMT) Received: from li-218185cc-29b5-11b2-a85c-9a1300ae2e6e.in.ibm.com (unknown [9.109.215.183]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 15 Sep 2025 15:03:21 +0000 (GMT) From: Donet Tom To: Andrew Morton , David Hildenbrand Cc: Ritesh Harjani , Xu Xin , Chengming Zhou , Wei Yang , Aboorva Devarajan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Giorgi Tchankvetadze , Donet Tom Subject: [PATCH v2 3/3] selftests/mm: Added fork test to verify global ksm_zero_pages counter behavior Date: Mon, 15 Sep 2025 20:33:06 +0530 Message-ID: <5910cb6bfc7c43b169b679a0108667a56d7ebdb8.1757946863.git.donettom@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-GUID: ZXyxwX1ucZr2gUZwipFy9t7yA4Xbn7EM X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTE1MDA4NiBTYWx0ZWRfX4G5L7Xf8orpF YrFigQN0bXgzJCxVV7kr3vYqAtOCkAMRmoN1Dyi/zv3wNRrgmP3trUgqVDAf1zqGeNwlwGLpkeu sW7I7G29lLsmw4sCAE+SacaAQw5FN41DCLe6/zO5GVY+0EZMl1hc2jgbrwm3PV9ALJd17QMz7a2 nGZ8RIX37iwnTfBMlbh2jMXIYTkAJT3tgL7jv54g4UB6KHeMDNFzsQhn8L3fPb0p1qyssitq1BE GV+Sf000ZYaLxcJjk/DaWmUM+Rch/YFTFkCzcx570hdk+4vHdrYCEJhyiBlPhP0v/MvY/U9+Rhs ppXe7x+TxswxlYPGVBCL9gyXgJk1oXg9fqp57LO+1sP6Ca5RF9t+2MN6JtyjJHmcM2Zg0MiJWBg l4WfQjmd X-Proofpoint-ORIG-GUID: KlHLGoZtd7BO7u8AJEiCdnV-7phG6b92 X-Authority-Analysis: v=2.4 cv=UJ7dHDfy c=1 sm=1 tr=0 ts=68c82ac1 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=yJojWOMRYYMA:10 a=VnNF1IyMAAAA:8 a=2YreOkuNpnKIDl0BDdwA:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-15_05,2025-09-12_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 bulkscore=0 impostorscore=0 spamscore=0 priorityscore=1501 clxscore=1015 suspectscore=0 phishscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509150086 Content-Type: text/plain; charset="utf-8" Added a selftest to verify the behavior of the global KSM zero-page counter during fork. When a process forks, the per-process zero-page counter is inherited by the child, and the global counter should be updated with this inherited value. This test ensures that the global counter is correctly updated after fork. Signed-off-by: Donet Tom --- .../selftests/mm/ksm_functional_tests.c | 74 ++++++++++++++++++- 1 file changed, 73 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/test= ing/selftests/mm/ksm_functional_tests.c index 645cefba2126..f23597ac8066 100644 --- a/tools/testing/selftests/mm/ksm_functional_tests.c +++ b/tools/testing/selftests/mm/ksm_functional_tests.c @@ -602,6 +602,77 @@ static void test_prot_none(void) munmap(map, size); } =20 +long ksm_get_global_ksm_zero_pages(void) +{ + int global_ksm_zero_pages_fd; + char buf[10]; + ssize_t ret; + + global_ksm_zero_pages_fd =3D open("/sys/kernel/mm/ksm/ksm_zero_pages", + O_RDONLY); + if (global_ksm_zero_pages_fd < 0) + return -errno; + + ret =3D pread(global_ksm_zero_pages_fd, buf, sizeof(buf) - 1, 0); + close(global_ksm_zero_pages_fd); + if (ret <=3D 0) + return -errno; + buf[ret] =3D 0; + + return strtol(buf, NULL, 10); +} + +static void test_fork_global_ksm_zero_pages_count(void) +{ + const unsigned int size =3D 2 * MiB; + char *map; + pid_t child_pid; + int status; + long g_zpages_before =3D 0, g_zpages_after =3D 0; + + ksft_print_msg("[RUN] %s\n", __func__); + + /* Unmerge all pages before test */ + if (ksm_stop() < 0) { + ksft_test_result_fail("KSM unmerging failed\n"); + return; + } + /* Get the global zero page count before test */ + g_zpages_before =3D ksm_get_global_ksm_zero_pages(); + /* Let KSM deduplicate zero pages. */ + map =3D mmap_and_merge_range(0x00, size, PROT_READ | PROT_WRITE, KSM_MERG= E_MADVISE); + if (map =3D=3D MAP_FAILED) + return; + + child_pid =3D fork(); + if (!child_pid) { + exit(ksm_stop()); + } else if (child_pid < 0) { + ksft_test_result_fail("fork() failed\n"); + return; + } + if (waitpid(child_pid, &status, 0) < 0) { + ksft_test_result_fail("waitpid() failed\n"); + return; + } + status =3D WEXITSTATUS(status); + if (status < 0) { + ksft_test_result_fail("KSM unmerging failed in child\n"); + return; + } + + /* Verify global zero-page count remains unchanged */ + g_zpages_after =3D ksm_get_global_ksm_zero_pages(); + if (g_zpages_before !=3D g_zpages_after) { + ksft_test_result_fail("Incorrect global ksm zero page count after fork\n= "); + return; + } + + ksft_test_result_pass("Global ksm zero page count is correct after fork\n= "); + ksm_stop(); + munmap(map, size); +} + static void test_fork_ksm_merging_page_count(void) { const unsigned int size =3D 2 * MiB; @@ -659,7 +730,7 @@ static void init_global_file_handles(void) =20 int main(int argc, char **argv) { - unsigned int tests =3D 9; + unsigned int tests =3D 10; int err; =20 if (argc > 1 && !strcmp(argv[1], FORK_EXEC_CHILD_PRG_NAME)) { @@ -692,6 +763,7 @@ int main(int argc, char **argv) test_prctl_fork_exec(); test_prctl_unmerge(); test_fork_ksm_merging_page_count(); + test_fork_global_ksm_zero_pages_count(); =20 err =3D ksft_get_fail_cnt(); if (err) --=20 2.51.0