Re: [PATCH v3 4/7] mm/selftests: Fix split_huge_page_test failure on systems with 64KB page size

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

On Tue, Jul 29, 2025 at 11:04:00AM +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")
>Reviewed-by: Dev Jain <dev.jain@arm.com>
>Reviewed-by: Zi Yan <ziy@nvidia.com>
>Co-developed-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
>Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
>Signed-off-by: Donet Tom <donettom@linux.ibm.com>
>---
> .../selftests/mm/split_huge_page_test.c       | 23 ++++++++++++-------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
>diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>index 05de1fc0005b..718daceb5282 100644
>--- a/tools/testing/selftests/mm/split_huge_page_test.c
>+++ b/tools/testing/selftests/mm/split_huge_page_test.c
>@@ -36,6 +36,7 @@ uint64_t pmd_pagesize;
> 
> #define PFN_MASK     ((1UL<<55)-1)
> #define KPF_THP      (1UL<<22)
>+#define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))
> 
> int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
> {
>@@ -522,6 +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();
> 
>@@ -533,35 +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 = GET_ORDER(nr_pages);

There is a sz2ord() in cow.c and uffd-wp-mremap.c.

Maybe we can factor it into vm_util.h and use it here.

-- 
Wei Yang
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