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

Wei Yang
2025-08-21T03:41:56Z

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?

>>
>> > 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
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