Re: [PATCH mm-unstable v15 09/13] mm/khugepaged: introduce collapse_allowable_orders helper function

David Hildenbrand (Arm)
2026-03-12T21:09:22Z

On 2/26/26 04:25, 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>
> ---
> mm/khugepaged.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 2e66d660ee8e..2fdfb6d42cf9 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -486,12 +486,22 @@ static unsigned int collapse_max_ptes_none(unsigned int order)
> return -EINVAL;
> }
>
> +/* 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)

Nit: one tab to much

> +{
> + enum tva_type tva_flags = is_khugepaged ? TVA_KHUGEPAGED : TVA_FORCED_COLLAPSE;
> + unsigned long orders = BIT(HPAGE_PMD_ORDER);
> +
> + return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
> +}
> +
> void khugepaged_enter_vma(struct vm_area_struct *vma,
> vm_flags_t vm_flags)
> {
> 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, /*is_khugepaged=*/true))
> __khugepaged_enter(vma->vm_mm);
> }
> }
> @@ -2637,7 +2647,7 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, enum scan_result *
> progress++;
> break;
> }
> - if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
> + if (!collapse_allowable_orders(vma, vma->vm_flags, /*is_khugepaged=*/true)) {

I'm not sure if converting from a perfectly readable enum to a boolean
is an improvement?

I would just keep the TVA_KHUGEPAGED / TVA_FORCED_COLLAPSE here/

If you want to catch callers passing in something else, you could likely
use a BUILD_BUG_ON in there.

--
Cheers,

David