On Fri, Dec 19, 2025 at 02:54:40PM +0530, Garg, Shivank wrote:
>
>
>On 12/17/2025 8:18 AM, Wei Yang wrote:
>> On Tue, Dec 16, 2025 at 11:11:38AM +0000, Shivank Garg wrote:
>>> Replace 'goto skip' with actual logic for better code readability.
>>>
>>> No functional change.
>>>
>>> Signed-off-by: Shivank Garg <[email protected]>
>>> ---
>>> mm/khugepaged.c | 7 ++++---
>>> 1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>>> index 6c8c35d3e0c9..107146f012b1 100644
>>> --- a/mm/khugepaged.c
>>> +++ b/mm/khugepaged.c
>>> @@ -2442,14 +2442,15 @@ static unsigned int
>>> khugepaged_scan_mm_slot(unsigned int pages, int *result,
>>> break;
>>> }
>>> if (!thp_vma_allowable_order(vma, vma->vm_flags,
>>> TVA_KHUGEPAGED, PMD_ORDER)) {
>>> -skip:
>>> progress++;
>>> continue;
>>> }
>>> hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE);
>>> hend = round_down(vma->vm_end, HPAGE_PMD_SIZE);
>>> - if (khugepaged_scan.address > hend)
>>> - goto skip;
>>> + if (khugepaged_scan.address > hend) {
>>> + progress++;
>>> + continue;
>>> + }
>>
>> Hi, Shivank
>>
>> The change here looks good, while I come up with an question.
>>
>> The @progress here seems record two things:
>>
>> * number of pages scaned
>> * number of vma skipped
>>
>Three things: number of mm. It's incremented 1 for whole
>khugepaged_scan_mm_slot().
>
Agree.
>
>> While in very rare case, we may miss to count the second case.
>>
>> For example, we have following vmas in a process:
>>
>> vma1 vma2
>> +----------------+------------+
>> |2M |1M |
>> +----------------+------------+
>>
>> Let's assume vma1 is exactly HPAGE_PMD_SIZE and also HPAGE_PMD_SIZE aligned.
>> But vma2 is only half of HPAGE_PMD_SIZE.
>>
>> When scan finish vma1 and start on vma2, we would have hstart = hend =
>> address. So we continue here but would not do real scan, since address ==
>> hend.
>>
>> I am thinking whether this could handle it:
>>
>> if (khugepaged_scan.address > hend || hend <= hstart) {
>> progress++;
>> continue;
>> }
>>
>> Do you thinks I am correct on this?
>
>I think you're correct.
>IIUC, @progress acts as rate limiter here.
>
>It is increasing +1 for whole, and then increases by +1 per VMA (if skipped),
>or by +HPAGE_PMD_NR (if actually scanned).
>
>So, progress ensuring the hugepaged_do_scan run only until (progress >= pages)
>at which point it yields and sleeps (wait_event_freezable).
>
>Without your suggested fix, if a process contains a large number of small VMAs
>(where
>round_up hstart >= round_down(hend), it will unfairly consume more CPU cycles
>before
>yielding compared to a process with fewer or aligned VMAs.
You are right. While I am not sure it exists in reality, but in theory it
could be.
>
>I think your suggestion is ensuring fairness by charging 'progress' count
>correctly.
>
Thanks for your confirmation. Would you mind add a cleanup in next version, or
you prefer me to send it :-)
>Thanks,
>Shivank
--
Wei Yang
Help you, Help me
