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Wed, 27 Aug 2025 18:03:15 GMT Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5307258043; Wed, 27 Aug 2025 18:03:15 +0000 (GMT) Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5B8BD58060; Wed, 27 Aug 2025 18:03:12 +0000 (GMT) Received: from [9.124.214.234] (unknown [9.124.214.234]) by smtpav06.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 27 Aug 2025 18:03:12 +0000 (GMT) Message-ID: <0c724a5c-3317-4bc6-b9ba-98b073934b66@linux.ibm.com> Date: Wed, 27 Aug 2025 23:33:11 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] selftests/mm: add fork inheritance test for ksm_merging_pages counter To: David Hildenbrand , Andrew Morton Cc: Ritesh Harjani , Xu Xin , Chengming Zhou , Wei Yang , Aboorva Devarajan , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <2e662107e01417bf9af23bc7f52863cd538419be.1756211338.git.donettom@linux.ibm.com> <88d6d5f08ff119625fa9accaa7b849dd77f9df25.1756211338.git.donettom@linux.ibm.com> Content-Language: en-US From: Donet Tom In-Reply-To: Content-Type: text/plain; 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This helps >> ensure correctness of KSM accounting across process creation. >> >> Signed-off-by: Donet Tom >> --- >>   .../selftests/mm/ksm_functional_tests.c       | 42 ++++++++++++++++++- >>   1 file changed, 41 insertions(+), 1 deletion(-) >> >> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c >> b/tools/testing/selftests/mm/ksm_functional_tests.c >> index 712f43c87736..d971394c9567 100644 >> --- a/tools/testing/selftests/mm/ksm_functional_tests.c >> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c >> @@ -602,6 +602,45 @@ static void test_prot_none(void) >>       munmap(map, size); >>   } >>   +static void test_fork_ksm_merging_page(void) >> +{ >> +    const unsigned int size = 2 * MiB; >> +    char *map; >> +    pid_t child_pid; >> +    int status; >> + >> +    ksft_print_msg("[RUN] %s\n", __func__); >> + >> +    map = mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, >> KSM_MERGE_MADVISE); >> +    if (map == MAP_FAILED) >> +        return; >> + >> +    child_pid = fork(); >> +    if (!child_pid) { >> +        int mpages; >> + >> +        init_global_file_handles(); >> +        mpages = ksm_get_self_merging_pages(); >> +        if (mpages > 0) >> +            ksft_test_result_fail("ksm_merging_page in child: %d\n", >> mpages); >> + >> +        exit(0); >> +    } 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; >> +    } >> + >> +    ksft_test_result_pass("ksm_merging_pages is not inherited after >> fork\n"); > > Won't this trigger a fail in the child and a pass in the parent process? > > You should likely instead let the child return the result (or the > number) and check that here. Thanks for pointing this out. I will make the change in the next version