[PATCH RFC 4/9] mm: skip zeroing in vma_alloc_zeroed_movable_folio for pre-zeroed pages

[Michael S. Tsirkin]

Use __GFP_PREZEROED and folio_test_clear_prezeroed() 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@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
---
 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..b649e7e315f4 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -322,8 +322,10 @@ struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
 {
 	struct folio *folio;
 
-	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
-	if (folio && user_alloc_needs_zeroing())
+	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_PREZEROED,
+			       0, vma, vaddr);
+	if (folio && user_alloc_needs_zeroing() &&
+	    !folio_test_clear_prezeroed(folio))
 		clear_user_highpage(&folio->page, vaddr);
 
 	return folio;
-- 
MST