Re: [PATCH v8 6/6] selftest: add a testcase of ksm zero pages

[David Hildenbrand <david@redhat.com>]

On 22.05.23 12:54, Yang Yang wrote:
> From: xu xin <xu.xin16@zte.com.cn>
> 
> Add a function test_unmerge_zero_page() to test the functionality on
> unsharing and counting ksm-placed zero pages and counting of this patch
> series.
> 
> test_unmerge_zero_page() actually contains three subjct test objects:
> (1) whether the count of ksm zero pages can update correctly after merging;
> (2) whether the count of ksm zero pages can update correctly after
>      unmerging;
> (3) whether ksm zero pages are really unmerged.
> 
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
> Reviewed-by: Xiaokai Ran <ran.xiaokai@zte.com.cn>
> Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
> ---
>   tools/testing/selftests/mm/ksm_functional_tests.c | 75 +++++++++++++++++++++++
>   1 file changed, 75 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 26853badae70..9b7fb94ed64f 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -29,6 +29,8 @@
>   
>   static int ksm_fd;
>   static int ksm_full_scans_fd;
> +static int ksm_zero_pages_fd;
> +static int ksm_use_zero_pages_fd;
>   static int pagemap_fd;
>   static size_t pagesize;
>   
> @@ -59,6 +61,21 @@ static bool range_maps_duplicates(char *addr, unsigned long size)
>   	return false;
>   }
>   
> +static long get_ksm_zero_pages(void)
> +{
> +	char buf[20];
> +	ssize_t read_size;
> +	unsigned long ksm_zero_pages;
> +

I would add:

if (!ksm_zero_pages_fd)
	return 0;

> +	read_size = pread(ksm_zero_pages_fd, buf, sizeof(buf) - 1, 0);
> +	if (read_size < 0)
> +		return -errno;
> +	buf[read_size] = 0;
> +	ksm_zero_pages = strtol(buf, NULL, 10);
> +
> +	return ksm_zero_pages;
> +}
> +
>   static long ksm_get_full_scans(void)
>   {
>   	char buf[10];
> @@ -159,6 +176,61 @@ static void test_unmerge(void)
>   	munmap(map, size);
>   }
>   
> +static inline unsigned long expected_ksm_pages(unsigned long mergeable_size)
> +{
> +	return mergeable_size / pagesize;
> +}

I suggest to just inline that.

> +
> +static void test_unmerge_zero_pages(void)
> +{
> +	const unsigned int size = 2 * MiB;
> +	char *map;
> +	unsigned long pages_expected;
> +
> +	ksft_print_msg("[RUN] %s\n", __func__);
> +
> +	/* Confirm the interfaces*/

Missing space at the end of the comment. But I suggest to just drop this comment.

> +	if (ksm_zero_pages_fd < 0) {
> +		ksft_test_result_skip("open(\"/sys/kernel/mm/ksm/ksm_zero_pages\") failed\n");
> +		return;
> +	}
> +	if (ksm_use_zero_pages_fd < 0) {
> +		ksft_test_result_skip("open \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
> +		return;
> +	}
> +	if (write(ksm_use_zero_pages_fd, "1", 1) != 1) {
> +		ksft_test_result_skip("write \"/sys/kernel/mm/ksm/use_zero_pages\" failed\n");
> +		return;
> +	}
> +
> +	/* Mmap zero pages*/

Missing space at the end of the comment

> +	map = mmap_and_merge_range(0x00, size, false);
> +	if (map == MAP_FAILED)
> +		return;
> +
> +	/* Check if ksm_zero_pages can be update correctly after merging */
> +	pages_expected = expected_ksm_pages(size);
> +	ksft_test_result(pages_expected == get_ksm_zero_pages(),
> +		"The count zero_page_sharing was updated after merging\n");
> +

Make sure that the number of tests (ksft_test_result*() invocations) is on any return
path as expected (e.g., 1).

if (pages_expected != get_ksm_zero_pages) {
	ksft_test_result_pass("'zero_page_sharing' updated after merging\n");
	goto unmap;
}

> +	/* try to unmerge half of the region */
> +	if (madvise(map, size / 2, MADV_UNMERGEABLE)) {
> +		ksft_test_result_fail("MADV_UNMERGEABLE failed\n");
> +		goto unmap;
> +	}
> +
> +	/* Check if ksm_zero_pages can be update correctly after unmerging */
> +	pages_expected = expected_ksm_pages(size / 2);

Just do

pages_expected /= 2;

> +	ksft_test_result(pages_expected == get_ksm_zero_pages(),
> +		"The count zero_page_sharing was updated after unmerging\n");
> +

if (pages_expected == get_ksm_zero_pages()) {
	ksft_test_result_pass("'zero_page_sharing' updated after unmerging\n");
	goto unmap;
}

> +	/* Check if ksm zero pages are really unmerged */
> +	ksft_test_result(!range_maps_duplicates(map, size / 2),
> +				"KSM zero pages were unmerged\n");
> +unmap:
> +	munmap(map, size);
> +}
> +
>   static void test_unmerge_discarded(void)
>   {
>   	const unsigned int size = 2 * MiB;
> @@ -379,8 +451,11 @@ int main(int argc, char **argv)
>   	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
>   	if (pagemap_fd < 0)
>   		ksft_exit_skip("open(\"/proc/self/pagemap\") failed\n");
> +	ksm_zero_pages_fd = open("/sys/kernel/mm/ksm/ksm_zero_pages", O_RDONLY);
> +	ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);
>   
>   	test_unmerge();
> +	test_unmerge_zero_pages();
>   	test_unmerge_discarded();
>   #ifdef __NR_userfaultfd
>   	test_unmerge_uffd_wp();

You should need something like this:

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 26853badae70..00df05bfc3a3 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -358,7 +358,7 @@ static void test_prctl_unmerge(void)
  
  int main(int argc, char **argv)
  {
-	unsigned int tests = 5;
+	unsigned int tests = 6;
  	int err;
  
  #ifdef __NR_userfaultfd

-- 
Thanks,

David / dhildenb