* [PATCH 2/2] mm: gup: cleanup the gup_fast_*() call chain
2026-02-19 5:02 [PATCH 0/2] mm: gup: cleanup gup_fast call chain Aristeu Rozanski
2026-02-19 5:02 ` [PATCH 1/2] mm: gup: move pmd_protnone() into gup_fast_pmd_leaf() Aristeu Rozanski
@ 2026-02-19 5:02 ` Aristeu Rozanski
2026-02-19 9:42 ` David Hildenbrand (Arm)
1 sibling, 1 reply; 5+ messages in thread
From: Aristeu Rozanski @ 2026-02-19 5:02 UTC (permalink / raw)
To: linux-mm
Cc: Andrew Morton, David Hildenbrand, Jason Gunthorpe, John Hubbard,
Peter Xu
Refactor gup_fast functions so each step of the way returns the number of
pages pinned. Because the previous step of the chain knows what the number
it should be, less indicates an error. This way there's no need to pass *nr
along.
Suggested-by: David Hildenbrand <david@kernel.org>
Link: https://lore.kernel.org/all/85e760cf-b994-40db-8d13-221feee55c60@redhat.com/T/#u
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Aristeu Rozanski <aris@ruivo.org>
---
mm/gup.c | 179 +++++++++++++++++++++++++++++++++------------------------------
1 file changed, 94 insertions(+), 85 deletions(-)
--- a/mm/gup.c 2026-02-18 23:39:10.187019351 -0500
+++ b/mm/gup.c 2026-02-18 23:39:10.185510090 -0500
@@ -2826,11 +2826,11 @@ static bool gup_fast_folio_allowed(struc
* also check pmd here to make sure pmd doesn't change (corresponds to
* pmdp_collapse_flush() in the THP collapse code path).
*/
-static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
- unsigned long end, unsigned int flags, struct page **pages,
- int *nr)
+static unsigned long gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp,
+ unsigned long addr, unsigned long end,
+ unsigned int flags, struct page **pages)
{
- int ret = 0;
+ unsigned long nr_pages = 0;
pte_t *ptep, *ptem;
ptem = ptep = pte_offset_map(&pmd, addr);
@@ -2892,15 +2892,13 @@ static int gup_fast_pte_range(pmd_t pmd,
goto pte_unmap;
}
folio_set_referenced(folio);
- pages[*nr] = page;
- (*nr)++;
+ pages[nr_pages] = page;
+ nr_pages++;
} while (ptep++, addr += PAGE_SIZE, addr != end);
- ret = 1;
-
pte_unmap:
pte_unmap(ptem);
- return ret;
+ return nr_pages;
}
#else
@@ -2913,21 +2911,21 @@ pte_unmap:
* get_user_pages_fast_only implementation that can pin pages. Thus it's still
* useful to have gup_fast_pmd_leaf even if we can't operate on ptes.
*/
-static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
- unsigned long end, unsigned int flags, struct page **pages,
- int *nr)
+static unsigned long gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp,
+ unsigned long addr, unsigned long end,
+ unsigned int flags, struct page **pages)
{
return 0;
}
#endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
-static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
- unsigned long end, unsigned int flags, struct page **pages,
- int *nr)
+static unsigned long gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp,
+ unsigned long addr, unsigned long end,
+ unsigned int flags, struct page **pages)
{
struct page *page;
struct folio *folio;
- int refs;
+ unsigned long nr_pages, i;
/* See gup_fast_pte_range() */
if (pmd_protnone(orig))
@@ -2939,42 +2937,40 @@ static int gup_fast_pmd_leaf(pmd_t orig,
if (pmd_special(orig))
return 0;
- refs = (end - addr) >> PAGE_SHIFT;
+ nr_pages = (end - addr) >> PAGE_SHIFT;
page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
- folio = try_grab_folio_fast(page, refs, flags);
+ folio = try_grab_folio_fast(page, nr_pages, flags);
if (!folio)
return 0;
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
- gup_put_folio(folio, refs, flags);
+ gup_put_folio(folio, nr_pages, flags);
return 0;
}
if (!gup_fast_folio_allowed(folio, flags)) {
- gup_put_folio(folio, refs, flags);
+ gup_put_folio(folio, nr_pages, flags);
return 0;
}
if (!pmd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
- gup_put_folio(folio, refs, flags);
+ gup_put_folio(folio, nr_pages, flags);
return 0;
}
- pages += *nr;
- *nr += refs;
- for (; refs; refs--)
+ for (i = 0; i < nr_pages; i++)
*(pages++) = page++;
folio_set_referenced(folio);
- return 1;
+ return nr_pages;
}
-static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
- unsigned long end, unsigned int flags, struct page **pages,
- int *nr)
+static unsigned long gup_fast_pud_leaf(pud_t orig, pud_t *pudp,
+ unsigned long addr, unsigned long end,
+ unsigned int flags, struct page **pages)
{
struct page *page;
struct folio *folio;
- int refs;
+ unsigned long nr_pages = 0, i;
if (!pud_access_permitted(orig, flags & FOLL_WRITE))
return 0;
@@ -2982,41 +2978,39 @@ static int gup_fast_pud_leaf(pud_t orig,
if (pud_special(orig))
return 0;
- refs = (end - addr) >> PAGE_SHIFT;
+ nr_pages = (end - addr) >> PAGE_SHIFT;
page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
- folio = try_grab_folio_fast(page, refs, flags);
+ folio = try_grab_folio_fast(page, nr_pages, flags);
if (!folio)
return 0;
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
- gup_put_folio(folio, refs, flags);
+ gup_put_folio(folio, nr_pages, flags);
return 0;
}
if (!gup_fast_folio_allowed(folio, flags)) {
- gup_put_folio(folio, refs, flags);
+ gup_put_folio(folio, nr_pages, flags);
return 0;
}
if (!pud_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
- gup_put_folio(folio, refs, flags);
+ gup_put_folio(folio, nr_pages, flags);
return 0;
}
- pages += *nr;
- *nr += refs;
- for (; refs; refs--)
+ for (i = 0; i < nr_pages; i++)
*(pages++) = page++;
folio_set_referenced(folio);
- return 1;
+ return nr_pages;
}
-static int gup_fast_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
- unsigned long end, unsigned int flags, struct page **pages,
- int *nr)
+static unsigned long gup_fast_pmd_range(pud_t *pudp, pud_t pud,
+ unsigned long addr, unsigned long end,
+ unsigned int flags, struct page **pages)
{
- unsigned long next;
+ unsigned long next, nr_pages = 0, chunk_nr_pages;
pmd_t *pmdp;
pmdp = pmd_offset_lockless(pudp, pud, addr);
@@ -3025,26 +3019,30 @@ static int gup_fast_pmd_range(pud_t *pud
next = pmd_addr_end(addr, end);
if (!pmd_present(pmd))
- return 0;
+ break;
if (unlikely(pmd_leaf(pmd))) {
- if (!gup_fast_pmd_leaf(pmd, pmdp, addr, next, flags,
- pages, nr))
- return 0;
-
- } else if (!gup_fast_pte_range(pmd, pmdp, addr, next, flags,
- pages, nr))
- return 0;
+ chunk_nr_pages = gup_fast_pmd_leaf(pmd, pmdp, addr,
+ next, flags,
+ &pages[nr_pages]);
+
+ } else
+ chunk_nr_pages = gup_fast_pte_range(pmd, pmdp, addr,
+ next, flags,
+ &pages[nr_pages]);
+ nr_pages += chunk_nr_pages;
+ if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+ break;
} while (pmdp++, addr = next, addr != end);
- return 1;
+ return nr_pages;
}
-static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr,
- unsigned long end, unsigned int flags, struct page **pages,
- int *nr)
+static unsigned long gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d,
+ unsigned long addr, unsigned long end,
+ unsigned int flags, struct page **pages)
{
- unsigned long next;
+ unsigned long next, nr_pages = 0, chunk_nr_pages;
pud_t *pudp;
pudp = pud_offset_lockless(p4dp, p4d, addr);
@@ -3053,24 +3051,27 @@ static int gup_fast_pud_range(p4d_t *p4d
next = pud_addr_end(addr, end);
if (unlikely(!pud_present(pud)))
- return 0;
- if (unlikely(pud_leaf(pud))) {
- if (!gup_fast_pud_leaf(pud, pudp, addr, next, flags,
- pages, nr))
- return 0;
- } else if (!gup_fast_pmd_range(pudp, pud, addr, next, flags,
- pages, nr))
- return 0;
+ break;
+ if (unlikely(pud_leaf(pud)))
+ chunk_nr_pages = gup_fast_pud_leaf(pud, pudp, addr,
+ next, flags,
+ &pages[nr_pages]);
+ else
+ chunk_nr_pages = gup_fast_pmd_range(pudp, pud, addr,
+ next, flags,
+ &pages[nr_pages]);
+ nr_pages += chunk_nr_pages;
+ if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+ break;
} while (pudp++, addr = next, addr != end);
- return 1;
+ return nr_pages;
}
-static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
- unsigned long end, unsigned int flags, struct page **pages,
- int *nr)
+static unsigned long gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
+ unsigned long end, unsigned int flags, struct page **pages)
{
- unsigned long next;
+ unsigned long next, nr_pages = 0, chunk_nr_pages;
p4d_t *p4dp;
p4dp = p4d_offset_lockless(pgdp, pgd, addr);
@@ -3079,20 +3080,23 @@ static int gup_fast_p4d_range(pgd_t *pgd
next = p4d_addr_end(addr, end);
if (!p4d_present(p4d))
- return 0;
+ break;
BUILD_BUG_ON(p4d_leaf(p4d));
- if (!gup_fast_pud_range(p4dp, p4d, addr, next, flags,
- pages, nr))
- return 0;
+ chunk_nr_pages = gup_fast_pud_range(p4dp, p4d, addr, next,
+ flags, &pages[nr_pages]);
+ nr_pages += chunk_nr_pages;
+ if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+ break;
} while (p4dp++, addr = next, addr != end);
- return 1;
+ return nr_pages;
}
-static void gup_fast_pgd_range(unsigned long addr, unsigned long end,
- unsigned int flags, struct page **pages, int *nr)
+static unsigned long gup_fast_pgd_range(unsigned long addr,
+ unsigned long end, unsigned int flags,
+ struct page **pages)
{
- unsigned long next;
+ unsigned long next, nr_pages = 0, chunk_nr_pages;
pgd_t *pgdp;
pgdp = pgd_offset(current->mm, addr);
@@ -3101,17 +3105,23 @@ static void gup_fast_pgd_range(unsigned
next = pgd_addr_end(addr, end);
if (pgd_none(pgd))
- return;
+ break;
BUILD_BUG_ON(pgd_leaf(pgd));
- if (!gup_fast_p4d_range(pgdp, pgd, addr, next, flags,
- pages, nr))
- return;
+ chunk_nr_pages = gup_fast_p4d_range(pgdp, pgd, addr, next,
+ flags, &pages[nr_pages]);
+ nr_pages += chunk_nr_pages;
+ if (chunk_nr_pages != (next - addr) >> PAGE_SHIFT)
+ break;
} while (pgdp++, addr = next, addr != end);
+
+ return nr_pages;
}
#else
-static inline void gup_fast_pgd_range(unsigned long addr, unsigned long end,
- unsigned int flags, struct page **pages, int *nr)
+static inline unsigned long gup_fast_pgd_range(unsigned long addr,
+ unsigned long end, unsigned int flags,
+ struct page **pages)
{
+ return 0;
}
#endif /* CONFIG_HAVE_GUP_FAST */
@@ -3129,8 +3139,7 @@ static bool gup_fast_permitted(unsigned
static unsigned long gup_fast(unsigned long start, unsigned long end,
unsigned int gup_flags, struct page **pages)
{
- unsigned long flags;
- int nr_pinned = 0;
+ unsigned long flags, nr_pinned = 0;
unsigned seq;
if (!IS_ENABLED(CONFIG_HAVE_GUP_FAST) ||
@@ -3154,7 +3163,7 @@ static unsigned long gup_fast(unsigned l
* that come from callers of tlb_remove_table_sync_one().
*/
local_irq_save(flags);
- gup_fast_pgd_range(start, end, gup_flags, pages, &nr_pinned);
+ nr_pinned = gup_fast_pgd_range(start, end, gup_flags, pages);
local_irq_restore(flags);
/*
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