Re: [PATCH v2 4/7] mm/selftests: Fix split_huge_page_test failure on systems with 64KB page size

[Zi Yan <ziy@nvidia.com>]

On 3 Jul 2025, at 2:06, 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")
> Signed-off-by: Donet Tom <donettom@linux.ibm.com>
> Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
> ---
>  .../selftests/mm/split_huge_page_test.c       | 23 ++++++++++++++-----
>  1 file changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index aa7400ed0e99..38296a758330 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -514,6 +514,15 @@ void split_thp_in_pagecache_to_order_at(size_t fd_size, const char *fs_loc,
>  	}
>  }
>
> +static unsigned int get_order(unsigned int pages)
> +{
> +	unsigned int order = 0;
> +
> +	while ((1U << order) < pages)
> +		order++;
> +	return order;
> +}
> +
>  int main(int argc, char **argv)
>  {
>  	int i;
> @@ -523,6 +532,7 @@ int main(int argc, char **argv)
>  	const char *fs_loc;
>  	bool created_tmp;
>  	int offset;
> +	unsigned int max_order;
>
>  	ksft_print_header();
>
> @@ -534,32 +544,33 @@ 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");
>
> +	max_order = get_order(pmd_pagesize/pagesize);

pmd_pagesize/pagesize is reused below, a tmp variable would be good.

> +	ksft_set_plan(1+(max_order-1)+1+max_order+max_order+(max_order-1)*4+2);
> +
>  	fd_size = 2 * pmd_pagesize;
>
>  	split_pmd_zero_pages();
>
> -	for (i = 0; i < 9; i++)
> +	for (i = 0; i < max_order; i++)
>  		if (i != 1)
>  			split_pmd_thp_to_order(i);
>
>  	split_pte_mapped_thp();
> -	for (i = 0; i < 9; i++)
> +	for (i = 0; i < max_order; i++)
>  		split_file_backed_thp(i);
>
>  	created_tmp = prepare_thp_fs(optional_xfs_path, fs_loc_template,
>  			&fs_loc);
> -	for (i = 8; i >= 0; i--)
> +	for (i = (max_order-1); i >= 0; i--)
>  		split_thp_in_pagecache_to_order_at(fd_size, fs_loc, i, -1);
>
> -	for (i = 0; i < 9; i++)
> +	for (i = 0; i < max_order; i++)
>  		for (offset = 0;
>  		     offset < pmd_pagesize / pagesize;
>  		     offset += MAX(pmd_pagesize / pagesize / 4, 1 << i))

With the change to get_order() proposed by David and ksft_set_plan()
simplification, Reviewed-by: Zi Yan <ziy@nvidia.com>

Best Regards,
Yan, Zi