On 12/20/2025 6:08 AM, Wei Yang wrote:
> 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 :-)
Sure, I'll add this fix patch in the next version.
Thanks,
Shivank
