linux-kernel - Re: [PATCH v3 1/3] mm: add get_and_clear_ptes() and clear

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Message-ID: <2dfb2d7a-40c4-4ab6-be71-4a03670ea994@linux.alibaba.com>
Date: Wed, 23 Jul 2025 11:29:08 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org, david@...hat.com
Cc: ziy@...dia.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 npache@...hat.com, ryan.roberts@....com, baohua@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] mm: add get_and_clear_ptes() and clear_ptes()



On 2025/7/22 23:05, Dev Jain wrote:
> From: David Hildenbrand <david@...hat.com>
> 
> From: David Hildenbrand <david@...hat.com>
> 
> Let's add variants to be used where "full" does not apply -- which will
> be the majority of cases in the future. "full" really only applies if
> we are about to tear down a full MM.
> 
> Use get_and_clear_ptes() in existing code, clear_ptes() users will
> be added next.
> 
> Should we make these inline functions instead and add separate docs?
> Probably not worth it for now.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Dev Jain <dev.jain@....com>

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

> ---
>   arch/arm64/mm/mmu.c     | 2 +-
>   include/linux/pgtable.h | 6 ++++++
>   mm/mremap.c             | 2 +-
>   mm/rmap.c               | 2 +-
>   4 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index abd9725796e9..20a89ab97dc5 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1528,7 +1528,7 @@ early_initcall(prevent_bootmem_remove_init);
>   pte_t modify_prot_start_ptes(struct vm_area_struct *vma, unsigned long addr,
>   			     pte_t *ptep, unsigned int nr)
>   {
> -	pte_t pte = get_and_clear_full_ptes(vma->vm_mm, addr, ptep, nr, /* full = */ 0);
> +	pte_t pte = get_and_clear_ptes(vma->vm_mm, addr, ptep, nr);
>   
>   	if (alternative_has_cap_unlikely(ARM64_WORKAROUND_2645198)) {
>   		/*
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index e3b99920be05..e45986b54277 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -736,6 +736,9 @@ static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm,
>   }
>   #endif
>   
> +#define get_and_clear_ptes(_mm, _addr, _ptep, _nr) \
> +	get_and_clear_full_ptes(_mm, _addr, _ptep, _nr, 0)
> +
>   #ifndef clear_full_ptes
>   /**
>    * clear_full_ptes - Clear present PTEs that map consecutive pages of the same
> @@ -768,6 +771,9 @@ static inline void clear_full_ptes(struct mm_struct *mm, unsigned long addr,
>   }
>   #endif
>   
> +#define clear_ptes(_mm, _addr, _ptep, _nr) \
> +	clear_full_ptes(_mm, _addr, _ptep, _nr, 0)
> +
>   /*
>    * If two threads concurrently fault at the same page, the thread that
>    * won the race updates the PTE and its local TLB/Cache. The other thread
> diff --git a/mm/mremap.c b/mm/mremap.c
> index ac39845e9718..677a4d744df9 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -280,7 +280,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
>   							 old_pte, max_nr_ptes);
>   			force_flush = true;
>   		}
> -		pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, nr_ptes, 0);
> +		pte = get_and_clear_ptes(mm, old_addr, old_ptep, nr_ptes);
>   		pte = move_pte(pte, old_addr, new_addr);
>   		pte = move_soft_dirty_pte(pte);
>   
> diff --git a/mm/rmap.c b/mm/rmap.c
> index f93ce27132ab..568198e9efc2 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -2036,7 +2036,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>   			flush_cache_range(vma, address, end_addr);
>   
>   			/* Nuke the page table entry. */
> -			pteval = get_and_clear_full_ptes(mm, address, pvmw.pte, nr_pages, 0);
> +			pteval = get_and_clear_ptes(mm, address, pvmw.pte, nr_pages);
>   			/*
>   			 * We clear the PTE but do not flush so potentially
>   			 * a remote CPU could still be writing to the folio.