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References: <20230418051342.1919757-1-shr@devkernel.io>
 <20230418152849.505124-1-david@redhat.com>
 <20230418152849.505124-3-david@redhat.com>
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From:   Stefan Roesch <shr@devkernel.io>
To:     David Hildenbrand <david@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-s390@vger.kernel.org, linux-kselftest@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@surriel.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH v1 2/3] selftests/ksm: ksm_functional_tests: add prctl
 unmerge test
Date:   Thu, 20 Apr 2023 14:30:57 -0700
In-reply-to: <20230418152849.505124-3-david@redhat.com>
Message-ID: <qvqwmt32i6kt.fsf@devbig1114.prn1.facebook.com>
MIME-Version: 1.0
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David Hildenbrand <david@redhat.com> writes:

> Let's test whether setting PR_SET_MEMORY_MERGE to 0 after setting it to
> 1 will unmerge pages, similar to how setting MADV_UNMERGEABLE after setting
> MADV_MERGEABLE would.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  .../selftests/mm/ksm_functional_tests.c       | 46 ++++++++++++++++---
>  1 file changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 7bc9fc17c9f0..26853badae70 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -91,9 +91,10 @@ static int ksm_merge(void)
>  	return 0;
>  }
>
> -static char *mmap_and_merge_range(char val, unsigned long size)
> +static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
>  {
>  	char *map;
> +	int ret;
>
>  	map = mmap(NULL, size, PROT_READ|PROT_WRITE,
>  		   MAP_PRIVATE|MAP_ANON, -1, 0);
> @@ -110,7 +111,17 @@ static char *mmap_and_merge_range(char val, unsigned long size)
>
>  	/* Make sure each page contains the same values to merge them. */
>  	memset(map, val, size);
> -	if (madvise(map, size, MADV_MERGEABLE)) {
> +
> +	if (use_prctl) {
> +		ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
> +		if (ret < 0 && errno == EINVAL) {
> +			ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
> +			goto unmap;
> +		} else if (ret) {
> +			ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
> +			goto unmap;
> +		}
> +	} else if (madvise(map, size, MADV_MERGEABLE)) {
>  		ksft_test_result_fail("MADV_MERGEABLE failed\n");
>  		goto unmap;
>  	}
> @@ -133,7 +144,7 @@ static void test_unmerge(void)
>
>  	ksft_print_msg("[RUN] %s\n", __func__);
>
> -	map = mmap_and_merge_range(0xcf, size);
> +	map = mmap_and_merge_range(0xcf, size, false);
>  	if (map == MAP_FAILED)
>  		return;
>
> @@ -155,7 +166,7 @@ static void test_unmerge_discarded(void)
>
>  	ksft_print_msg("[RUN] %s\n", __func__);
>
> -	map = mmap_and_merge_range(0xcf, size);
> +	map = mmap_and_merge_range(0xcf, size, false);
>  	if (map == MAP_FAILED)
>  		return;
>
> @@ -187,7 +198,7 @@ static void test_unmerge_uffd_wp(void)
>
>  	ksft_print_msg("[RUN] %s\n", __func__);
>
> -	map = mmap_and_merge_range(0xcf, size);
> +	map = mmap_and_merge_range(0xcf, size, false);
>  	if (map == MAP_FAILED)
>  		return;
>
> @@ -323,9 +334,31 @@ static void test_prctl_fork(void)
>  	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
>  }
>
> +static void test_prctl_unmerge(void)
> +{
> +	const unsigned int size = 2 * MiB;
> +	char *map;
> +
> +	ksft_print_msg("[RUN] %s\n", __func__);
> +
> +	map = mmap_and_merge_range(0xcf, size, true);
> +	if (map == MAP_FAILED)
> +		return;
> +
> +	if (prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0)) {
> +		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
> +		goto unmap;
> +	}
> +
> +	ksft_test_result(!range_maps_duplicates(map, size),
> +			 "Pages were unmerged\n");
> +unmap:
> +	munmap(map, size);
> +}
> +
>  int main(int argc, char **argv)
>  {
> -	unsigned int tests = 4;
> +	unsigned int tests = 5;
>  	int err;
>
>  #ifdef __NR_userfaultfd
> @@ -355,6 +388,7 @@ int main(int argc, char **argv)
>
>  	test_prctl();
>  	test_prctl_fork();
> +	test_prctl_unmerge();
>
>  	err = ksft_get_fail_cnt();
>  	if (err)

Acked-by: Stefan Roesch <shr@devkernel.io>