linux-kernel - Re: [PATCH v10 03/13] khugepaged: generalize hugepage_vma

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Message-ID: <cd4dd743-679f-4c55-9635-6d32e6fa5ff7@lucifer.local>
Date: Wed, 20 Aug 2025 14:23:09 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Nico Pache <npache@...hat.com>
Cc: linux-mm@...ck.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        david@...hat.com, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
        Liam.Howlett@...cle.com, ryan.roberts@....com, dev.jain@....com,
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        mhocko@...e.com, rdunlap@...radead.org, hughd@...gle.com
Subject: Re: [PATCH v10 03/13] khugepaged: generalize hugepage_vma_revalidate
 for mTHP support

On Tue, Aug 19, 2025 at 07:41:55AM -0600, 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 the order is enabled.
>
> To ensure madvise_collapse can support working on mTHP orders without the
> PMD order enabled, we need to convert hugepage_vma_revalidate to take a
> bitmap of orders.
>
> No functional change in this patch.
>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.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 (modulo nit/query below) so:

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

> ---
>  mm/khugepaged.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b7b98aebb670..2d192ec961d2 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -917,7 +917,7 @@ static int collapse_find_target_node(struct collapse_control *cc)
>  static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
>  				   bool expect_anon,
>  				   struct vm_area_struct **vmap,
> -				   struct collapse_control *cc)
> +				   struct collapse_control *cc, unsigned long orders)
>  {
>  	struct vm_area_struct *vma;
>  	enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED :
> @@ -930,9 +930,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
>  	if (!vma)
>  		return SCAN_VMA_NULL;
>
> +	/* Always check the PMD order to insure its not shared by another VMA */

NIT: ensure not insure.

>  	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, orders))
>  		return SCAN_VMA_CHECK;
>  	/*
>  	 * Anon VMA expected, the address may be unmapped then
> @@ -1134,7 +1135,8 @@ 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,
> +					 BIT(HPAGE_PMD_ORDER));

Shouldn't this be PMD order? Seems equivalent.

>  	if (result != SCAN_SUCCEED) {
>  		mmap_read_unlock(mm);
>  		goto out_nolock;
> @@ -1168,7 +1170,8 @@ 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,
> +					 BIT(HPAGE_PMD_ORDER));
>  	if (result != SCAN_SUCCEED)
>  		goto out_up_write;
>  	/* check if the pmd is still valid */
> @@ -2807,7 +2810,7 @@ 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, BIT(HPAGE_PMD_ORDER));
>  			if (result  != SCAN_SUCCEED) {
>  				last_fail = result;
>  				goto out_nolock;
> --
> 2.50.1
>