On 28.08.25 18:37, Lorenzo Stoakes wrote:
On Thu, Aug 28, 2025 at 12:01:22AM +0200, David Hildenbrand wrote:
nth_page() is no longer required when iterating over pages within a
single folio, so let's just drop it when recording subpages.
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
This looks correct to me, so notwithtsanding suggestion below, LGTM and:
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
---
mm/gup.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index b2a78f0291273..89ca0813791ab 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -488,12 +488,11 @@ static int record_subpages(struct page *page, unsigned long sz,
unsigned long addr, unsigned long end,
struct page **pages)
{
- struct page *start_page;
int nr;
- start_page = nth_page(page, (addr & (sz - 1)) >> PAGE_SHIFT);
+ page += (addr & (sz - 1)) >> PAGE_SHIFT;
for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
- pages[nr] = nth_page(start_page, nr);
+ pages[nr] = page++;
This is really nice, but I wonder if (while we're here) we can't be even
more clear as to what's going on here, e.g.:
static int record_subpages(struct page *page, unsigned long sz,
unsigned long addr, unsigned long end,
struct page **pages)
{
size_t offset_in_folio = (addr & (sz - 1)) >> PAGE_SHIFT;
struct page *subpage = page + offset_in_folio;
for (; addr != end; addr += PAGE_SIZE)
*pages++ = subpage++;
return nr;
}
Or some variant of that with the masking stuff self-documented.
What about the following cleanup on top:
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;
}
The nice thing is that we only record pages in the array if they actually passed our tests.
--
Cheers
David / dhildenb
