Re: [PATCH v4 3/3] vfio/type1: optimize vfio_unpin_pages_remote() for large folio

[David Hildenbrand]

On 17.06.25 14:42, lizhe.67@xxxxxxxxxxxxx wrote:
> On Tue, 17 Jun 2025 11:49:43 +0200, david@xxxxxxxxxx wrote:
>   
> > On 17.06.25 11:47, lizhe.67@xxxxxxxxxxxxx wrote:
> > > On Tue, 17 Jun 2025 09:43:56 +0200, david@xxxxxxxxxx wrote:
> > >    
> > > > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > > > > index e952bf8bdfab..d7653f4c10d5 100644
> > > > > --- a/drivers/vfio/vfio_iommu_type1.c
> > > > > +++ b/drivers/vfio/vfio_iommu_type1.c
> > > > > @@ -801,16 +801,43 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> > > > >            return pinned;
> > > > >     }
> > > > >     
> > > > > +/* Returned number includes the provided current page. */
> > > > > +static inline unsigned long folio_remaining_pages(struct folio *folio,
> > > > > +               struct page *page, unsigned long max_pages)
> > > > > +{
> > > > > +       if (!folio_test_large(folio))
> > > > > +               return 1;
> > > > > +       return min_t(unsigned long, max_pages,
> > > > > +                    folio_nr_pages(folio) - folio_page_idx(folio, page));
> > > > > +}
> > > >
> > > > Note that I think that should go somewhere into mm.h, and also get used
> > > > by GUP. So factoring it out from GUP and then using it here.
> > >
> > > I think I need to separate this out into a distinct patch within the
> > > patchset. Is that correct?
> >
> > Yes, that's what I would do.
>
> How do you think of this implementation?
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 242b05671502..eb91f99ea973 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2165,6 +2165,23 @@ static inline long folio_nr_pages(const struct folio *folio)
>          return folio_large_nr_pages(folio);
>   }
>   
> +/*
> + * folio_remaining_pages - Counts the number of pages from a given
> + * start page to the end of the folio.
> + *
> + * @folio: Pointer to folio
> + * @start_page: The starting page from which to begin counting.
> + *
> + * Returned number includes the provided start page.
> + *
> + * The caller must ensure that @start_page belongs to @folio.
> + */
> +static inline unsigned long folio_remaining_pages(struct folio *folio,
> +               struct page *start_page)
> +{
> +       return folio_nr_pages(folio) - folio_page_idx(folio, start_page);
> +}
> +
>   /* Only hugetlbfs can allocate folios larger than MAX_ORDER */
>   #ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
>   #define MAX_FOLIO_NR_PAGES     (1UL << PUD_ORDER)
> diff --git a/mm/gup.c b/mm/gup.c
> index 15debead5f5b..14ae2e3088b4 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -242,7 +242,7 @@ static inline struct folio *gup_folio_range_next(struct page *start,
>   
>          if (folio_test_large(folio))
>                  nr = min_t(unsigned int, npages - i,
> -                          folio_nr_pages(folio) - folio_page_idx(folio, next));
> +                          folio_remaining_pages(folio, next));
>   
>          *ntails = nr;
>          return folio;
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index b2fc5266e3d2..34e85258060c 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -96,7 +96,7 @@ static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long e
>                                  return page;
>                          }
>   
> -                       skip_pages = folio_nr_pages(folio) - folio_page_idx(folio, page);
> +                       skip_pages = folio_remaining_pages(folio, page);
>                          pfn += skip_pages - 1;
>                          continue;
>                  }
> ---

Guess I would have pulled the "min" in there, but passing something like 
ULONG_MAX for the page_isolation case also looks rather ugly.

--
Cheers,

David / dhildenb