linux-kernel - Re: [PATCH v12 mm-new 03/15] khugepaged: generalize hugepage_vma

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Message-ID: <bbadcbfa-0250-4d53-975e-97b81559c6ad@linux.dev>
Date: Mon, 27 Oct 2025 17:02:54 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: Nico Pache <npache@...hat.com>
Cc: david@...hat.com, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, ryan.roberts@....com,
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 linux-kernel@...r.kernel.org, sunnanyong@...wei.com, vishal.moola@...il.com,
 thomas.hellstrom@...ux.intel.com, yang@...amperecomputing.com,
 kas@...nel.org, linux-doc@...r.kernel.org, linux-mm@...ck.org,
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 rdunlap@...radead.org, hughd@...gle.com, richard.weiyang@...il.com,
 vbabka@...e.cz, rppt@...nel.org, jannh@...gle.com, pfalcato@...e.de
Subject: Re: [PATCH v12 mm-new 03/15] khugepaged: generalize
 hugepage_vma_revalidate for mTHP support



On 2025/10/23 02:37, Nico Pache wrote:
> For khugepaged to support different mTHP orders, we must generalize this
> to check if the PMD is not shared by another VMA and that the order is
> enabled.
> 
> No functional change in this patch. Also correct a comment about the
> functionality of the revalidation.
> 
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> Co-developed-by: Dev Jain <dev.jain@....com>
> Signed-off-by: Dev Jain <dev.jain@....com>
> Signed-off-by: Nico Pache <npache@...hat.com>
> ---

LGTM!

Reviewed-by: Lance Yang <lance.yang@...ux.dev>

>   mm/khugepaged.c | 20 +++++++++++---------
>   1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 36e31d99e507..6cf8700823f9 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -893,14 +893,13 @@ static int collapse_find_target_node(struct collapse_control *cc)
>   
>   /*
>    * If mmap_lock temporarily dropped, revalidate vma
> - * before taking mmap_lock.
> + * after taking the mmap_lock again.
>    * Returns enum scan_result value.
>    */
>   
>   static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> -				   bool expect_anon,
> -				   struct vm_area_struct **vmap,
> -				   struct collapse_control *cc)
> +		bool expect_anon, struct vm_area_struct **vmap,
> +		struct collapse_control *cc, unsigned int order)
>   {
>   	struct vm_area_struct *vma;
>   	enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED :
> @@ -913,15 +912,16 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
>   	if (!vma)
>   		return SCAN_VMA_NULL;
>   
> +	/* Always check the PMD order to ensure its not shared by another VMA */
>   	if (!thp_vma_suitable_order(vma, address, PMD_ORDER))
>   		return SCAN_ADDRESS_RANGE;
> -	if (!thp_vma_allowable_order(vma, vma->vm_flags, type, PMD_ORDER))
> +	if (!thp_vma_allowable_orders(vma, vma->vm_flags, type, BIT(order)))
>   		return SCAN_VMA_CHECK;
>   	/*
>   	 * Anon VMA expected, the address may be unmapped then
>   	 * remapped to file after khugepaged reaquired the mmap_lock.
>   	 *
> -	 * thp_vma_allowable_order may return true for qualified file
> +	 * thp_vma_allowable_orders may return true for qualified file
>   	 * vmas.
>   	 */
>   	if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap)))
> @@ -1117,7 +1117,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
>   		goto out_nolock;
>   
>   	mmap_read_lock(mm);
> -	result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
> +	result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
> +					 HPAGE_PMD_ORDER);
>   	if (result != SCAN_SUCCEED) {
>   		mmap_read_unlock(mm);
>   		goto out_nolock;
> @@ -1151,7 +1152,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
>   	 * mmap_lock.
>   	 */
>   	mmap_write_lock(mm);
> -	result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
> +	result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
> +					 HPAGE_PMD_ORDER);
>   	if (result != SCAN_SUCCEED)
>   		goto out_up_write;
>   	/* check if the pmd is still valid */
> @@ -2792,7 +2794,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>   			mmap_read_lock(mm);
>   			mmap_locked = true;
>   			result = hugepage_vma_revalidate(mm, addr, false, &vma,
> -							 cc);
> +							 cc, HPAGE_PMD_ORDER);
>   			if (result  != SCAN_SUCCEED) {
>   				last_fail = result;
>   				goto out_nolock;