Re: [PATCH v13 mm-new 03/16] khugepaged: generalize hugepage_vma_revalidate for mTHP support

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

OK I'll stop reporting the merge conflicts from the that series but yeah here
too I guess it kills a whole bunch :)

On Mon, Dec 01, 2025 at 10:46:14AM -0700, 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: Wei Yang <richard.weiyang@gmail.com>
> Reviewed-by: Lance Yang <lance.yang@linux.dev>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Co-developed-by: Dev Jain <dev.jain@arm.com>
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> Signed-off-by: Nico Pache <npache@redhat.com>
> ---
>  mm/khugepaged.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 433ea7283488..69fc6b41f010 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -892,14 +892,13 @@ 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 :
> @@ -912,15 +911,16 @@ 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 */
> @@ -2814,7 +2816,7 @@ 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;
> --
> 2.51.1
>