Re: [PATCH] selftests/mm: fix split_huge_page_test for folio_split() tests.

[Zi Yan <ziy@nvidia.com>]

On 11 Jul 2025, at 9:29, David Hildenbrand wrote:

> On 09.07.25 03:27, Zi Yan wrote:
>> PID_FMT does not have an offset field, so folio_split() tests are not
>> performed. Add PID_FMT_OFFSET with an offset field and use it to perform
>> folio_split() tests.
>>
>> Fixes: 80a5c494c89f ("selftests/mm: add tests for folio_split(), buddy allocator like split")
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>>   tools/testing/selftests/mm/split_huge_page_test.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index aa7400ed0e99..f0d9c035641d 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -31,6 +31,7 @@ uint64_t pmd_pagesize;
>>   #define INPUT_MAX 80
>>    #define PID_FMT "%d,0x%lx,0x%lx,%d"
>> +#define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
>>   #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>>    #define PFN_MASK     ((1UL<<55)-1)
>> @@ -483,7 +484,7 @@ void split_thp_in_pagecache_to_order_at(size_t fd_size, const char *fs_loc,
>>   		write_debugfs(PID_FMT, getpid(), (uint64_t)addr,
>>   			      (uint64_t)addr + fd_size, order);
>>   	else
>> -		write_debugfs(PID_FMT, getpid(), (uint64_t)addr,
>> +		write_debugfs(PID_FMT_OFFSET, getpid(), (uint64_t)addr,
>>   			      (uint64_t)addr + fd_size, order, offset);
>>    	for (i = 0; i < fd_size; i++)
>
> So I assume the tests still passed. Would there be a way to have made them fail? (IOW, detect that the wrong kind-of split was performed)

Only if the initial PMD page is not split. To detect whether all after-split
folios are the size we expect, additional code that reads kpageflags
is needed. I will put it in my TODO to make this test more robust.

>
> Acked-by: David Hildenbrand <david@redhat.com>

Thanks.

Best Regards,
Yan, Zi