Re: [PATCH v10 03/13] khugepaged: generalize hugepage_vma_revalidate for mTHP support

Zi Yan
2025-08-21T14:09:20Z

On 20 Aug 2025, at 23:41, Wei Yang wrote:

> On Wed, Aug 20, 2025 at 09:40:40AM -0600, Nico Pache wrote:
> [...]
>>>
>>>> if (!thp_vma_suitable_order(vma, address, PMD_ORDER))
>>>> return SCAN_ADDRESS_RANGE;
>>>> - if (!thp_vma_allowable_order(vma, vma->vm_flags, type, PMD_ORDER))
>>>> + if (!thp_vma_allowable_orders(vma, vma->vm_flags, type, orders))
>>>> return SCAN_VMA_CHECK;
>>>> /*
>>>> * Anon VMA expected, the address may be unmapped then
>>>> @@ -1134,7 +1135,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
>>>> goto out_nolock;
>>>>
>>>> mmap_read_lock(mm);
>>>> - result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
>>>> + result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
>>>> + BIT(HPAGE_PMD_ORDER));
>>>
>>> Shouldn't this be PMD order? Seems equivalent.
>> Yeah i'm actually not sure why we have both... they seem to be the
>> same thing, but perhaps there is some reason for having two...
>
> I am confused with these two, PMD_ORDER above and HPAGE_PMD_ORDER from here.
>
> Do we have a guide on when to use which?

Looking at the definition of HPAGE_PMD_SHIFT in huge_mm.h, it will cause a
build bug when PMD level huge page is not supported. So I think
HPAGE_PMD_ORDER should be used for all huge pages (both THP and hugetlb).

>
>>>
>>>> if (result != SCAN_SUCCEED) {
>>>> mmap_read_unlock(mm);
>>>> goto out_nolock;
>>>> @@ -1168,7 +1170,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
>>>> * mmap_lock.
>>>> */
>>>> mmap_write_lock(mm);
>>>> - result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
>>>> + result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
>>>> + BIT(HPAGE_PMD_ORDER));
>>>> if (result != SCAN_SUCCEED)
>>>> goto out_up_write;
>>>> /* check if the pmd is still valid */
>>>> @@ -2807,7 +2810,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>>>> mmap_read_lock(mm);
>>>> mmap_locked = true;
>>>> result = hugepage_vma_revalidate(mm, addr, false, &vma,
>>>> - cc);
>>>> + cc, BIT(HPAGE_PMD_ORDER));
>>>> if (result != SCAN_SUCCEED) {
>>>> last_fail = result;
>>>> goto out_nolock;
>>>> --
>>>> 2.50.1
>>>>
>>>
>>
>
> --
> Wei Yang
> Help you, Help me

--
Best Regards,
Yan, Zi