Re: [PATCH v4 4/7] mm/selftests: Fix split_huge_page_test failure on systems with 64KB page size

[Wei Yang <richard.weiyang@gmail.com>]

On Sat, Aug 16, 2025 at 09:31:10AM +0530, Aboorva Devarajan wrote:
>From: Donet Tom <donettom@linux.ibm.com>
>
>The split_huge_page_test fails on systems with a 64KB base page size.
>This is because the order of a 2MB huge page is different:
>
>On 64KB systems, the order is 5.
>
>On 4KB systems, it's 9.
>
>The test currently assumes a maximum huge page order of 9, which is only
>valid for 4KB base page systems. On systems with 64KB pages, attempting
>to split huge pages beyond their actual order (5) causes the test to fail.
>
>In this patch, we calculate the huge page order based on the system's base
>page size. With this change, the tests now run successfully on both 64KB
>and 4KB page size systems.
>
>Fixes: fa6c02315f745 ("mm: huge_memory: a new debugfs interface for splitting THP tests")
>Co-developed-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
>Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
>Reviewed-by: Dev Jain <dev.jain@arm.com>
>Reviewed-by: Zi Yan <ziy@nvidia.com>
>Signed-off-by: Donet Tom <donettom@linux.ibm.com>

Reviewed-by: Wei Yang <richard.weiyang@gmail.com>

Nit below:

>---
> tools/testing/selftests/mm/cow.c              |  5 -----
> .../selftests/mm/split_huge_page_test.c       | 22 ++++++++++++-------
> tools/testing/selftests/mm/uffd-wp-mremap.c   |  5 -----
> tools/testing/selftests/mm/vm_util.h          |  5 +++++
> 4 files changed, 19 insertions(+), 18 deletions(-)
>
>diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
>index 90ee5779662f..e742d9313798 100644
>--- a/tools/testing/selftests/mm/cow.c
>+++ b/tools/testing/selftests/mm/cow.c
>@@ -41,11 +41,6 @@ static size_t hugetlbsizes[10];
> static int gup_fd;
> static bool has_huge_zeropage;
> 
>-static int sz2ord(size_t size)
>-{
>-	return __builtin_ctzll(size / pagesize);
>-}
>-
> static int detect_thp_sizes(size_t sizes[], int max)
> {
> 	int count = 0;
>diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>index eadbeb820d71..7cbeaebc9d71 100644
>--- a/tools/testing/selftests/mm/split_huge_page_test.c
>+++ b/tools/testing/selftests/mm/split_huge_page_test.c
>@@ -523,6 +523,9 @@ int main(int argc, char **argv)
> 	const char *fs_loc;
> 	bool created_tmp;
> 	int offset;
>+	unsigned int max_order;
>+	unsigned int nr_pages;
>+	unsigned int tests;
> 
> 	ksft_print_header();
> 
>@@ -534,35 +537,38 @@ int main(int argc, char **argv)
> 	if (argc > 1)
> 		optional_xfs_path = argv[1];
> 
>-	ksft_set_plan(1+8+1+9+9+8*4+2);
>-
> 	pagesize = getpagesize();
> 	pageshift = ffs(pagesize) - 1;
> 	pmd_pagesize = read_pmd_pagesize();
> 	if (!pmd_pagesize)
> 		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
> 
>+	nr_pages = pmd_pagesize / pagesize;
>+	max_order =  sz2ord(pmd_pagesize);
                    ^
		    extra space here

>+	tests = 2 + (max_order - 1) + (2 * max_order) + (max_order - 1) * 4 + 2;
>+	ksft_set_plan(tests);
>+
> 	fd_size = 2 * pmd_pagesize;
> 
> 	split_pmd_zero_pages();
> 

-- 
Wei Yang
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