[PATCH RFC v2 11/18] mm: skip zeroing in vma_alloc_zeroed_movable_folio for pre-zeroed pages

Michael S. Tsirkin
2026-04-20T12:51:02Z

Use vma_alloc_folio_hints() and check PGHINT_ZEROED to skip
clear_user_highpage() when the page is already zeroed.

On x86, vma_alloc_zeroed_movable_folio is overridden by a macro
that uses __GFP_ZERO directly, so this change has no effect there.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
include/linux/highmem.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index af03db851a1d..8bb67772c1cb 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -321,9 +321,11 @@ struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
unsigned long vaddr)
{
struct folio *folio;
+ pghint_t hints;

- folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
- if (folio && user_alloc_needs_zeroing())
+ folio = vma_alloc_folio_hints(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr,
+ &hints);
+ if (folio && user_alloc_needs_zeroing() && !(hints & PGHINT_ZEROED))
clear_user_highpage(&folio->page, vaddr);

return folio;
--
MST