Re: [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 <da...@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 <da...@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