Re: [PATCH v2 19/37] mm/gup: remove record_subpages() (Linux IDE and SATA Storage)

On 01.09.25 17:03, David Hildenbrand wrote:

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.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 mm/gup.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index c10cd969c1a3b..f0f4d1a68e094 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
@@ -2967,8 +2954,8 @@ 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)
@@ -2989,6 +2976,8 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	}

*nr += refs;

+	for (; refs; refs--)
+		*(pages++) = page++;
 	folio_set_referenced(folio);
 	return 1;
 }
@@ -3007,8 +2996,8 @@ 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)
@@ -3030,6 +3019,8 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
 	}

*nr += refs;

+	for (; refs; refs--)
+		*(pages++) = page++;
 	folio_set_referenced(folio);
 	return 1;
 }

Okay, this code is nasty. We should rework this code to just return the nr and receive a the proper
pages pointer, getting rid of the "*nr" parameter.
For the time being, the following should do the trick:
commit bfd07c995814354f6b66c5b6a72e96a7aa9fb73b (HEAD -> nth_page)
Author: David Hildenbrand <david@xxxxxxxxxx>
Date: Fri Sep 5 08:38:43 2025 +0200
 fixup: mm/gup: remove record_subpages()

pages is not adjusted by the caller, but idnexed by existing *nr.Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

diff --git a/mm/gup.c b/mm/gup.c
index 010fe56f6e132..22420f2069ee1 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2981,6 +2981,7 @@ 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++;
@@ -3024,6 +3025,7 @@ 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++;
--
Cheers
David / dhildenb