linux-kernel - Re: [PATCH v12 mm-new 11/15] khugepaged: introduce collapse_allowable

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Message-ID: <5b2dbd05-094f-452a-8067-d342b2819af9@lucifer.local>
Date: Thu, 6 Nov 2025 18:49:59 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Nico Pache <npache@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-doc@...r.kernel.org, david@...hat.com,
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Subject: Re: [PATCH v12 mm-new 11/15] khugepaged: introduce
 collapse_allowable_orders helper function

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@...ux.alibaba.com>
> Signed-off-by: Nico Pache <npache@...hat.com>

With nits below adddressed, LGTM so:

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