Re: [PATCH v12 mm-new 11/15] khugepaged: introduce collapse_allowable_orders helper function

Lorenzo Stoakes
2025-11-06T18:51:08Z

On Wed, Oct 22, 2025 at 12:37:13PM -0600, Nico Pache wrote:
> Add collapse_allowable_orders() to generalize THP order eligibility. The
> function determines which THP orders are permitted based on collapse
> context (khugepaged vs madv_collapse).
>
> This consolidates collapse configuration logic and provides a clean
> interface for future mTHP collapse support where the orders may be
> different.
>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Nico Pache <npache@redhat.com>

With nits below adddressed, LGTM so:

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

> ---
> mm/khugepaged.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 0dbbe04c31fe..89a105124790 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -489,7 +489,16 @@ static unsigned int collapse_max_ptes_none(unsigned int order, bool full_scan)
> max_ptes_none = min(khugepaged_max_ptes_none, HPAGE_PMD_NR/2 - 1);
>
> return max_ptes_none >> (HPAGE_PMD_ORDER - order);
> +}
> +
> +/* Check what orders are allowed based on the vma and collapse type */
> +static unsigned long collapse_allowable_orders(struct vm_area_struct *vma,
> + vm_flags_t vm_flags, bool is_khugepaged)
> +{
> + enum tva_type tva_flags = is_khugepaged ? TVA_KHUGEPAGED : TVA_FORCED_COLLAPSE;
> + unsigned long orders = BIT(HPAGE_PMD_ORDER);

Nit, but can const-ify.

>
> + return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
> }
>
> void khugepaged_enter_vma(struct vm_area_struct *vma,
> @@ -497,7 +506,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
> {
> if (!mm_flags_test(MMF_VM_HUGEPAGE, vma->vm_mm) &&
> hugepage_pmd_enabled()) {
> - if (thp_vma_allowable_order(vma, vm_flags, TVA_KHUGEPAGED, PMD_ORDER))
> + if (collapse_allowable_orders(vma, vm_flags, true))

If we have a 'mystery meat' boolean parameter can we always use the convention of:

collapse_allowable_orders(vma, vm_flags, /*is_khugepaged=*/true)

Please? Same goes for other invocations obviously.

> __khugepaged_enter(vma->vm_mm);
> }
> }
> @@ -2567,7 +2576,7 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, int *result,
> progress++;
> break;
> }
> - if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
> + if (!collapse_allowable_orders(vma, vma->vm_flags, true)) {
> skip:
> progress++;
> continue;
> @@ -2873,7 +2882,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
> BUG_ON(vma->vm_start > start);
> BUG_ON(vma->vm_end < end);
>
> - if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER))
> + if (!collapse_allowable_orders(vma, vma->vm_flags, false))
> return -EINVAL;
>
> cc = kmalloc(sizeof(*cc), GFP_KERNEL);
> --
> 2.51.0
>