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

[David Hildenbrand]

On 04.08.25 11:04, Wei Yang wrote:

On Tue, Jul 29, 2025 at 11:04:00AM +0530, Aboorva Devarajan wrote:

From: Donet Tom <donet...@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.j...@arm.com>
Reviewed-by: Zi Yan <z...@nvidia.com>
Co-developed-by: Aboorva Devarajan <aboor...@linux.ibm.com>
Signed-off-by: Aboorva Devarajan <aboor...@linux.ibm.com>
Signed-off-by: Donet Tom <donet...@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.

That sounds reasonable to me.

--
Cheers,

David / dhildenb