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

Lorenzo Stoakes
2025-08-20T13:24:48Z

On Tue, Aug 19, 2025 at 07:41:55AM -0600, Nico Pache wrote:
> For khugepaged to support different mTHP orders, we must generalize this
> to check if the PMD is not shared by another VMA and the order is enabled.
>
> To ensure madvise_collapse can support working on mTHP orders without the
> PMD order enabled, we need to convert hugepage_vma_revalidate to take a
> bitmap of orders.
>
> No functional change in this patch.
>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Co-developed-by: Dev Jain <dev.jain@arm.com>
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> Signed-off-by: Nico Pache <npache@redhat.com>

LGTM (modulo nit/query below) so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
> mm/khugepaged.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b7b98aebb670..2d192ec961d2 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -917,7 +917,7 @@ static int collapse_find_target_node(struct collapse_control *cc)
> static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> bool expect_anon,
> struct vm_area_struct **vmap,
> - struct collapse_control *cc)
> + struct collapse_control *cc, unsigned long orders)
> {
> struct vm_area_struct *vma;
> enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED :
> @@ -930,9 +930,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> if (!vma)
> return SCAN_VMA_NULL;
>
> + /* Always check the PMD order to insure its not shared by another VMA */

NIT: ensure not insure.

> 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.

> 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
>