mm/gup: remove record_subpages()

We can just cleanup the code by calculating the #refs earlier, so we can
just inline what remains of record_subpages().

Calculate the number of references/pages ahead of times, and record them
only once all our tests passed.

[david@redhat.com: fix `pages' adjustment]
  Link: https://lkml.kernel.org/r/cc7f03f8-da8b-407e-a03a-e8e5a9ec5462@redhat.com
Link: https://lkml.kernel.org/r/20250901150359.867252-20-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 17 deletions

diff --git a/mm/gup.c b/mm/gup.c
index e1bd2b2e9145..b8aee964421c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -484,19 +484,6 @@ static inline void mm_set_has_pinned_flag(struct mm_struct *mm)
 #ifdef CONFIG_MMU
 
 #ifdef CONFIG_HAVE_GUP_FAST
-static int record_subpages(struct page *page, unsigned long sz,
-			   unsigned long addr, unsigned long end,
-			   struct page **pages)
-{
-	int nr;
-
-	page += (addr & (sz - 1)) >> PAGE_SHIFT;
-	for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
-		pages[nr] = page++;
-
-	return nr;
-}
-
 /**
  * try_grab_folio_fast() - Attempt to get or pin a folio in fast path.
  * @page:  pointer to page to be grabbed
@@ -2971,8 +2958,8 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	if (pmd_special(orig))
 		return 0;
 
-	page = pmd_page(orig);
-	refs = record_subpages(page, PMD_SIZE, addr, end, pages + *nr);
+	refs = (end - addr) >> PAGE_SHIFT;
+	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 
 	folio = try_grab_folio_fast(page, refs, flags);
 	if (!folio)
@@ -2992,7 +2979,10 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 		return 0;
 	}
 
+	pages += *nr;
 	*nr += refs;
+	for (; refs; refs--)
+		*(pages++) = page++;
 	folio_set_referenced(folio);
 	return 1;
 }
@@ -3011,8 +3001,8 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
 	if (pud_special(orig))
 		return 0;
 
-	page = pud_page(orig);
-	refs = record_subpages(page, PUD_SIZE, addr, end, pages + *nr);
+	refs = (end - addr) >> PAGE_SHIFT;
+	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 
 	folio = try_grab_folio_fast(page, refs, flags);
 	if (!folio)
@@ -3033,7 +3023,10 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
 		return 0;
 	}
 
+	pages += *nr;
 	*nr += refs;
+	for (; refs; refs--)
+		*(pages++) = page++;
 	folio_set_referenced(folio);
 	return 1;
 }