linux-kernel - Re: [PATCH v13 mm-new 05/16] khugepaged: introduce is_mthp

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Message-ID: <CCE3840A-A46A-4F33-8412-FC55161A6D6C@nvidia.com>
Date: Tue, 02 Dec 2025 22:13:36 -0500
From: Zi Yan <ziy@...dia.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 v13 mm-new 05/16] khugepaged: introduce is_mthp_order
 helper

On 1 Dec 2025, at 12:46, Nico Pache wrote:

> In order to add mTHP support, we will often be checking if a given order
> is a mTHP or PMD order. Lets create a simple helper function to keep the
> code clean and readable.
>
> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Signed-off-by: Nico Pache <npache@...hat.com>
> ---
>  mm/khugepaged.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 8599c7fa112e..9c041141b2e3 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -338,6 +338,11 @@ static bool pte_none_or_zero(pte_t pte)
>  	return pte_present(pte) && is_zero_pfn(pte_pfn(pte));
>  }
>
> +static bool is_mthp_order(unsigned int order)
> +{
> +	return order != HPAGE_PMD_ORDER;
> +}
> +

The code at the bottom of __folio_split() in mm/huge_memory.c
can use this helper.

The code in deferred_split_folio() uses folio_test_pmd_mappable()
instead of order == HPAGE_PMD_ORDER, but the code can be changed
to use the helper.

>  int hugepage_madvise(struct vm_area_struct *vma,
>  		     vm_flags_t *vm_flags, int advice)
>  {
> @@ -1071,13 +1076,13 @@ static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
>  	folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask);
>  	if (!folio) {
>  		*foliop = NULL;
> -		if (order == HPAGE_PMD_ORDER)
> +		if (!is_mthp_order(order))
>  			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
>  		count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC_FAILED);
>  		return SCAN_ALLOC_HUGE_PAGE_FAIL;
>  	}
>
> -	if (order == HPAGE_PMD_ORDER)
> +	if (!is_mthp_order(order))
>  		count_vm_event(THP_COLLAPSE_ALLOC);
>  	count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC);
>
> -- 
> 2.51.1


Best Regards,
Yan, Zi