[PATCH v1 18/36] mm/gup: drop nth_page() usage within folio when recording subpages

[David Hildenbrand]

>>
>>
>> The nice thing is that we only record pages in the array if they actually passed our tests.
> 
> Yeah that's nice actually.
> 
> This is fine (not the meme :P)

:D

> 
> So yes let's do this!

That leaves us with the following on top of this patch:

 From 4533c6e3590cab0c53e81045624d5949e0ad9015 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david at redhat.com>
Date: Fri, 29 Aug 2025 15:41:45 +0200
Subject: [PATCH] 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.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
  mm/gup.c | 25 ++++++++-----------------
  1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 89ca0813791ab..5a72a135ec70b 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
@@ -2963,8 +2950,8 @@ 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)
@@ -2985,6 +2972,8 @@ 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;
  }
@@ -3003,8 +2992,8 @@ 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)
@@ -3026,6 +3015,8 @@ 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;
  }
-- 
2.50.1


-- 
Cheers

David / dhildenb