Re: [PATCH v1 18/36] mm/gup: drop nth_page() usage within folio when recording subpages
From: Lorenzo Stoakes <hidden>
Date: 2025-08-28 16:38:44
Also in:
dri-devel, intel-gfx, io-uring, kvm, linux-arm-kernel, linux-crypto, linux-ide, linux-iommu, linux-kselftest, linux-mips, linux-mm, linux-mmc, linux-riscv, linux-s390, linux-scsi, lkml, virtualization
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 <redacted>
This looks correct to me, so notwithtsanding suggestion below, LGTM and: Reviewed-by: Lorenzo Stoakes <redacted>
quoted hunk ↗ jump to hunk
--- 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.
quoted hunk ↗ jump to hunk
return nr; }@@ -1512,7 +1511,7 @@ static long __get_user_pages(struct mm_struct *mm, } for (j = 0; j < page_increm; j++) { - subpage = nth_page(page, j); + subpage = page + j; pages[i + j] = subpage; flush_anon_page(vma, subpage, start + j * PAGE_SIZE); flush_dcache_page(subpage); --2.50.1
Cheers, Lorenzo