Re: [PATCH] selftests/mm: directly add pagesize instead of increase until page size

[David Hildenbrand <david@redhat.com>]

On 31.08.25 03:32, Zi Yan wrote:
> On 29 Aug 2025, at 22:31, Wei Yang wrote:
> 
>> The check of is_backed_by_folio() is done on each page.
>>
>> Directly move pointer to next page instead of increase one and check if
>> it is page size aligned.
>>
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> ---
>>   tools/testing/selftests/mm/split_huge_page_test.c | 5 ++---
>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index 10ae65ea032f..7f7016ba4054 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -423,9 +423,8 @@ static void split_pte_mapped_thp(void)
>>
>>   	/* smap does not show THPs after mremap, use kpageflags instead */
>>   	thp_size = 0;
>> -	for (i = 0; i < pagesize * 4; i++)
>> -		if (i % pagesize == 0 &&
>> -		    is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd))
>> +	for (i = 0; i < pagesize * 4; i += pagesize)
>> +		if (is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd))
>>   			thp_size++;
>>
>>   	if (thp_size != 4)
> 
> It might be better to add
> 
> if (pte_mapped[i] != (char)i)
> 	ksft_exit_fail_msg("%ld byte corrupted\n", i);
> 
> instead to make sure mremap() does not change pte_mapped[] values.

We do have a corruption check later in that function, so I think we can 
just keep it simple here.

So this as is LGTM

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

As noted, we should just move from mremap() to mprotect() or sth like 
that which has clearer semantics.

-- 
Cheers

David / dhildenb