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

On 5 Aug 2026, at 21:17, Baolin Wang wrote:

> 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 <[email protected]>
>>> ---
>>>   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

Got it. If a single order covers the flow, I am fine with it.

> 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.

Right. I mean when one specifies ./khugepaged mthp_khugepaged:file/shmem, the
program should show some error like “file/shmem not supported”.


Best Regards,
Yan, Zi