linux-kernel - Re: [PATCH v4 2/3] gup: introduce unpin_user_folio_dirty

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Message-ID: <e09ed520-6b52-4b53-b6bb-dfee8f34be5b@redhat.com>
Date: Tue, 17 Jun 2025 09:35:00 +0200
From: David Hildenbrand <david@...hat.com>
To: lizhe.67@...edance.com, alex.williamson@...hat.com,
 akpm@...ux-foundation.org, peterx@...hat.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 2/3] gup: introduce unpin_user_folio_dirty_locked()

On 17.06.25 06:18, lizhe.67@...edance.com wrote:
> From: Li Zhe <lizhe.67@...edance.com>
> 
> Introduce a new interface, unpin_user_folio_dirty_locked(). This
> interface is similar to unpin_user_folio(), but it adds the
> capability to conditionally mark a folio as dirty. VFIO will utilize
> this interface to accelerate the VFIO DMA unmap process.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Li Zhe <lizhe.67@...edance.com>
> ---
>   include/linux/mm.h |  2 ++
>   mm/gup.c           | 27 +++++++++++++++++++++------
>   2 files changed, 23 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index fdda6b16263b..242b05671502 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1689,6 +1689,8 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
>   				      bool make_dirty);
>   void unpin_user_pages(struct page **pages, unsigned long npages);
>   void unpin_user_folio(struct folio *folio, unsigned long npages);
> +void unpin_user_folio_dirty_locked(struct folio *folio,
> +		unsigned long npins, bool make_dirty);
>   void unpin_folios(struct folio **folios, unsigned long nfolios);
>   
>   static inline bool is_cow_mapping(vm_flags_t flags)
> diff --git a/mm/gup.c b/mm/gup.c
> index 84461d384ae2..15debead5f5b 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -360,12 +360,7 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
>   
>   	for (i = 0; i < npages; i += nr) {
>   		folio = gup_folio_range_next(page, npages, i, &nr);
> -		if (make_dirty && !folio_test_dirty(folio)) {
> -			folio_lock(folio);
> -			folio_mark_dirty(folio);
> -			folio_unlock(folio);
> -		}
> -		gup_put_folio(folio, nr, FOLL_PIN);
> +		unpin_user_folio_dirty_locked(folio, nr, make_dirty);
>   	}
>   }
>   EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
> @@ -435,6 +430,26 @@ void unpin_user_folio(struct folio *folio, unsigned long npages)
>   }
>   EXPORT_SYMBOL(unpin_user_folio);
>   
> +/**
> + * unpin_user_folio_dirty_locked() - conditionally mark a folio
> + * dirty and unpin it
> + *
> + * @folio:  pointer to folio to be released
> + * @npins:  number of pins
> + * @make_dirty: whether to mark the folio dirty
> + *
> + * Mark the folio as being modified if @make_dirty is true. Then
> + * release npins of the folio.
> + */
> +void unpin_user_folio_dirty_locked(struct folio *folio,
> +		unsigned long npins, bool make_dirty)
> +{
> +	if (make_dirty && !folio_test_dirty(folio))
> +		folio_mark_dirty_lock(folio);
> +	gup_put_folio(folio, npins, FOLL_PIN);
> +}
> +EXPORT_SYMBOL_GPL(unpin_user_folio_dirty_locked);
> +
>   /**
>    * unpin_folios() - release an array of gup-pinned folios.
>    * @folios:  array of folios to be marked dirty and released.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb