linux-kernel - Re: [PATCH v4 3/3] vfio/type1: optimize vfio_unpin_pages

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Message-ID: <20250617124218.25727-1-lizhe.67@bytedance.com>
Date: Tue, 17 Jun 2025 20:42:18 +0800
From: lizhe.67@...edance.com
To: david@...hat.com
Cc: akpm@...ux-foundation.org,
	alex.williamson@...hat.com,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	lizhe.67@...edance.com,
	peterx@...hat.com
Subject: Re: [PATCH v4 3/3] vfio/type1: optimize vfio_unpin_pages_remote() for large folio

On Tue, 17 Jun 2025 11:49:43 +0200, david@...hat.com wrote:
 
> On 17.06.25 11:47, lizhe.67@...edance.com wrote:
> > On Tue, 17 Jun 2025 09:43:56 +0200, david@...hat.com 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;
                }
---

Thanks,
Zhe