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

[Zi Yan]

On 3 Jul 2025, at 4:58, Donet Tom wrote:

> On 7/3/25 1:52 PM, David Hildenbrand wrote:
>> On 03.07.25 08:06, Aboorva Devarajan wrote:
>>> From: Donet Tom <donettom@xxxxxxxxxxxxx>
>>>
>>> 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@xxxxxxxxxxxxx>
>>> Signed-off-by: Aboorva Devarajan <aboorvad@xxxxxxxxxxxxx>
>>> ---
>>>   .../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;
>>> +}
>>
>> I think this can simply be
>>
>> return 32 - __builtin_clz(pages - 1);
>>
>> That mimics what get_order() in the kernel does for BITS_PER_LONG == 32
>>
>> or simpler
>>
>> return 31 - __builtin_clz(pages);
>>
>> E.g., if pages=512, you get 31-22=9
>
>
> Sure David, We will  change it.
>
>
>>
>>> +
>>>   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);
>>> + ksft_set_plan(1+(max_order-1)+1+max_order+max_order+(max_order-1)*4+2);
>>
>> Wow. Can we simplify that in any sane way?
>
>
> It is counting test by test. Let me try to simplify it and send the next version.

Yeah, I did that (ksft_set_plan(1+8+1+9+9+8*4+2);) to count different tests
separately and in the same order as the following tests, so that I could
get ksft_set_plan number right when adding or removing tests. Maybe it is
fine to just sum them up now.

Best Regards,
Yan, Zi