linux-kernel - Re: [PATCH 3/3] mm/hugetlb: Refactor __unmap_hugepage

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Message-ID: <daaeffe6-f9b8-4923-a273-0dab573aa749@oracle.com>
Date: Thu, 17 Apr 2025 12:21:55 -0400
From: Sidhartha Kumar <sidhartha.kumar@...cle.com>
To: nifan.cxl@...il.com, muchun.song@...ux.dev, willy@...radead.org
Cc: mcgrof@...nel.org, a.manzanares@...sung.com, dave@...olabs.net,
        akpm@...ux-foundation.org, david@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Fan Ni <fan.ni@...sung.com>
Subject: Re: [PATCH 3/3] mm/hugetlb: Refactor __unmap_hugepage_range() to take
 folio instead of page

On 4/17/25 11:43 AM, nifan.cxl@...il.com wrote:
> From: Fan Ni <fan.ni@...sung.com>
> 
> The function __unmap_hugepage_range() has two kinds of users:
> 1) unmap_hugepage_range(), which passes in the head page of a folio.
>     Since unmap_hugepage_range() already takes folio and there are no other
>     uses of the folio struct in the function, it is natural for
>     __unmap_hugepage_range() to take folio also.
> 2) All other uses, which pass in NULL pointer.
> 
> In both cases, we can pass in folio. Refactor __unmap_hugepage_range() to
> take folio.
> 
> Signed-off-by: Fan Ni <fan.ni@...sung.com>
> ---
> 
> Question: If the change in the patch makes sense, should we try to convert all
> "page" uses in __unmap_hugepage_range() to folio?
> 

For this to be correct, we have to ensure that the pte in:

	page = pte_page(pte);

only refers to the pte of a head page. pte comes from:

	pte = huge_ptep_get(mm, address, ptep);

and in the for loop above:
		
	for (; address < end; address += sz)

address is incremented by the huge page size so I think address here 
only points to head pages of hugetlb folios and it would make sense to 
convert page to folio here.

> ---
>   include/linux/hugetlb.h |  2 +-
>   mm/hugetlb.c            | 10 +++++-----
>   2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index b7699f35c87f..d6c503dd2f7d 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -133,7 +133,7 @@ void unmap_hugepage_range(struct vm_area_struct *,
>   void __unmap_hugepage_range(struct mmu_gather *tlb,
>   			  struct vm_area_struct *vma,
>   			  unsigned long start, unsigned long end,
> -			  struct page *ref_page, zap_flags_t zap_flags);
> +			  struct folio *ref_folio, zap_flags_t zap_flags);
>   void hugetlb_report_meminfo(struct seq_file *);
>   int hugetlb_report_node_meminfo(char *buf, int len, int nid);
>   void hugetlb_show_meminfo_node(int nid);
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 3181dbe0c4bb..7d280ab23784 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5833,7 +5833,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma,
>   
>   void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
>   			    unsigned long start, unsigned long end,
> -			    struct page *ref_page, zap_flags_t zap_flags)
> +			    struct folio *ref_folio, zap_flags_t zap_flags)
>   {
>   	struct mm_struct *mm = vma->vm_mm;
>   	unsigned long address;
> @@ -5910,8 +5910,8 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
>   		 * page is being unmapped, not a range. Ensure the page we
>   		 * are about to unmap is the actual page of interest.
>   		 */
> -		if (ref_page) {
> -			if (page != ref_page) {
> +		if (ref_folio) {
> +			if (page != folio_page(ref_folio, 0)) {
>   				spin_unlock(ptl);
>   				continue;
>   			}
> @@ -5977,7 +5977,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
>   		/*
>   		 * Bail out after unmapping reference page if supplied
>   		 */
> -		if (ref_page)
> +		if (ref_folio)
>   			break;
>   	}
>   	tlb_end_vma(tlb, vma);
> @@ -6052,7 +6052,7 @@ void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
>   	tlb_gather_mmu(&tlb, vma->vm_mm);
>   
>   	__unmap_hugepage_range(&tlb, vma, start, end,
> -			       folio_page(ref_folio, 0), zap_flags);
> +			       ref_folio, zap_flags);
>   
>   	mmu_notifier_invalidate_range_end(&range);
>   	tlb_finish_mmu(&tlb);
Reviewed-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>