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

[Zi Yan]

On 5 Aug 2026, at 21:30, Baolin Wang wrote:

> On 8/6/26 9:25 AM, Zi Yan wrote:
>> 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 <baolin.wang@xxxxxxxxxxxxxxxxx>
>>>>> ---
>>>>>    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”.
>
> Yes, that works too. I still prefer to add the corresponding test cases after I add shmem mTHP collapse support:)

Sure. Or update usage() to print “mthp_khugepaged only supports anon”. You
can remove that after you add other support types.

>
> But if you have a strong opinion on this, I can also add a "not supported" message first.


Best Regards,
Yan, Zi