linux-kernel - Re: [PATCH v11 11/15] khugepaged: introduce collapse_allowable

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Message-ID: <50305e9f-ad03-4ce9-9ae7-0c657bd87ef0@linux.alibaba.com>
Date: Fri, 12 Sep 2025 17:24:50 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Nico Pache <npache@...hat.com>, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
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 mathieu.desnoyers@...icios.com, akpm@...ux-foundation.org,
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Subject: Re: [PATCH v11 11/15] khugepaged: introduce collapse_allowable_orders
 helper function



On 2025/9/12 11:28, 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.
> 
> Signed-off-by: Nico Pache <npache@...hat.com>

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

> ---
>   mm/khugepaged.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 5b45ef575446..d224fa97281a 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -485,7 +485,16 @@ static int collapse_max_ptes_none(unsigned int order)
>   	else
>   		max_ptes_none = khugepaged_max_ptes_none;
>   	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);
>   
> +	return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
>   }
>   
>   void khugepaged_enter_vma(struct vm_area_struct *vma,
> @@ -493,7 +502,7 @@ 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))
>   			__khugepaged_enter(vma->vm_mm);
>   	}
>   }
> @@ -2557,7 +2566,7 @@ 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;
> @@ -2865,7 +2874,7 @@ 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);