Re: [PATCH mm-unstable v19 10/14] mm/khugepaged: introduce collapse_possible_orders helper functions

[Lorenzo Stoakes]

On Fri, Jun 05, 2026 at 10:14:17AM -0600, Nico Pache wrote:
> Add collapse_possible_orders() to generalize THP order eligibility. The
> function determines which THP orders are permitted based on collapse
> context (khugepaged vs madv_collapse). We also add collapse_possible()
> as a thin wrapper around collapse_possible_orders() that returns a bool
> rather than the whole bitmap.
>
> This consolidates collapse configuration logic and provides a clean
> interface for future mTHP collapse support where the orders may be
> different.
>
> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Nico Pache <npache@xxxxxxxxxx>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>

> ---
>  mm/khugepaged.c | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 26c343a6fa3d..ec886a031952 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -554,12 +554,30 @@ void __khugepaged_enter(struct mm_struct *mm)
>  		wake_up_interruptible(&khugepaged_wait);
>  }
>
> +/*
> + * Check what orders are possible based on the vma and collapse type.
> + * This is used to determine if mTHP collapse is a viable option.
> + */
> +static unsigned long collapse_possible_orders(struct vm_area_struct *vma,
> +		vm_flags_t vm_flags, enum tva_type tva_flags)
> +{
> +	const unsigned long orders = BIT(HPAGE_PMD_ORDER);
> +
> +	return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
> +}
> +
> +static bool collapse_possible(struct vm_area_struct *vma,
> +		vm_flags_t vm_flags, enum tva_type tva_flags)
> +{
> +	return collapse_possible_orders(vma, vm_flags, tva_flags);
> +}
> +
>  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_possible(vma, vm_flags, TVA_KHUGEPAGED))
>  			__khugepaged_enter(vma->vm_mm);
>  	}
>  }
> @@ -2700,7 +2718,7 @@ static void collapse_scan_mm_slot(unsigned int progress_max,
>  			cc->progress++;
>  			break;
>  		}
> -		if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
> +		if (!collapse_possible(vma, vma->vm_flags, TVA_KHUGEPAGED)) {
>  			cc->progress++;
>  			continue;
>  		}
> @@ -3010,7 +3028,7 @@ 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_possible(vma, vma->vm_flags, TVA_FORCED_COLLAPSE))
>  		return -EINVAL;
>
>  	cc = kmalloc_obj(*cc);
> --
> 2.54.0
>