linux-kernel - Re: [PATCH v2 2/3] selftests/mm: Added fork inheritance test for ksm_merging

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Message-ID: <26e38fe5-e6c4-4678-8056-95c0ff4350e6@redhat.com>
Date: Wed, 17 Sep 2025 15:15:39 +0200
From: David Hildenbrand <david@...hat.com>
To: Donet Tom <donettom@...ux.ibm.com>,
 Andrew Morton <akpm@...ux-foundation.org>
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>
Subject: Re: [PATCH v2 2/3] selftests/mm: Added fork inheritance test for
 ksm_merging_pages counter

On 15.09.25 17:03, Donet Tom wrote:
> Added a new selftest to verify whether the `ksm_merging_pages` counter
> in `mm_struct` is not inherited by a child process after fork. This helps
> ensure correctness of KSM accounting across process creation.
> 
> Signed-off-by: Donet Tom <donettom@...ux.ibm.com>
> ---
>   .../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..645cefba2126 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_count(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) {
> +		init_global_file_handles();
> +		exit(ksm_get_self_merging_pages());
> +	} else if (child_pid < 0) {
> +		ksft_test_result_fail("fork() failed\n");
> +		return;

Probably
	goto out;

in all these fail cases

> +	}
> +
> +	if (waitpid(child_pid, &status, 0) < 0) {
> +		ksft_test_result_fail("waitpid() failed\n");
> +		return;
> +	}
> +
> +	status = WEXITSTATUS(status);
> +	if (status) {
> +		ksft_test_result_fail("ksm_merging_page in child: %d\n", status);
> +		return;
> +	}
> +
> +	ksft_test_result_pass("ksm_merging_pages is not inherited after fork\n");
> +

And have

	out:

here

With that:

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb