Re: [PATCH v2 4/4] selftests: mm: add mTHP collapse test cases

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 8/6/26 12:46 AM, Zi Yan wrote:
> On Sat Aug 1, 2026 at 2:26 AM EDT, Baolin Wang wrote:
>> Added a new command 'mthp_khugepaged' for mTHP collapse, along with the '-c'
>> parameter to specify the collapse order. Additionally, added mTHP collapse
>> test cases for 'collapse_full', 'collapse_empty', and 'collapse_single_mthp'
>> for anonymous folios. All khugepaged test cases passed.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> ---
>>   tools/testing/selftests/mm/khugepaged.c   | 130 ++++++++++++++++++----
>>   tools/testing/selftests/mm/run_vmtests.sh |   2 +
>>   2 files changed, 113 insertions(+), 19 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
>> index f69be6be0ecd..64d6da6aa90d 100644
>> --- a/tools/testing/selftests/mm/khugepaged.c
>> +++ b/tools/testing/selftests/mm/khugepaged.c
>> @@ -26,9 +26,11 @@
>>   
>>   #define BASE_ADDR ((void *)(1UL << 30))
>>   static unsigned long hpage_pmd_size;
>> +static int hpage_pmd_order;
>>   static unsigned long page_size;
>>   static int hpage_pmd_nr;
>>   static int anon_order;
>> +static int collapse_order;
> 
> <snip>
> 
>>   
>> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
>> index 687d115e3bd8..d09f9f6a384e 100755
>> --- a/tools/testing/selftests/mm/run_vmtests.sh
>> +++ b/tools/testing/selftests/mm/run_vmtests.sh
>> @@ -410,6 +410,8 @@ CATEGORY="thp" run_test ./khugepaged all:shmem
>>   
>>   CATEGORY="thp" run_test ./khugepaged -s 4 all:shmem
>>   
>> +CATEGORY="thp" run_test ./khugepaged -c 4 mthp_khugepaged:anon
> 
> Why only testing collapse_order == 4? It is more useful to test all
> possible mTHP orders. -c can accept common separated order and a range.

This also follows the previous '-s' parameter configuration, which is 
used to specify the mTHP order allocation.

I think specifying a single order size already tests the overall mTHP 
collapse flow, so I'm not sure whether testing all orders is worthwhile. 
Maybe I can add a few more orders?
./khugepaged -c 2 mthp_khugepaged:anon
./khugepaged -c 4 mthp_khugepaged:anon
./khugepaged -c 8 mthp_khugepaged:anon

> Why only testing mthp_khugepaged:anon? IIRC, file and shmem are not
> supported, so khugepaged should reject them, right?

Currently, I have not added test cases for shmem mTHP collapse, so 
adding file or shmem would be no-ops and might mislead others. I will 
add the shmem/file mTHP collapse feature and test cases in a following 
patchset.