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

["David Hildenbrand (Arm)" <david@kernel.org>]

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