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@redhat.com
This looks correct to me, so notwithtsanding suggestion below, LGTM and:
Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
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.