[PATCH RFC 6/9] mm: skip zeroing in vma_alloc_anon_folio_pmd for pre-zeroed pages

[Michael S. Tsirkin]

Use __GFP_PREZEROED and folio_test_clear_prezeroed() to skip
folio_zero_user() in the PMD THP anonymous page allocation path
when the page is already zeroed.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
---
 mm/huge_memory.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8e2746ea74ad..3b9b53fad0f1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1256,7 +1256,7 @@ EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
 static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 		unsigned long addr)
 {
-	gfp_t gfp = vma_thp_gfp_mask(vma);
+	gfp_t gfp = vma_thp_gfp_mask(vma) | __GFP_PREZEROED;
 	const int order = HPAGE_PMD_ORDER;
 	struct folio *folio;
 
@@ -1285,7 +1285,7 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 	* make sure that the page corresponding to the faulting address will be
 	* hot in the cache after zeroing.
 	*/
-	if (user_alloc_needs_zeroing())
+	if (user_alloc_needs_zeroing() && !folio_test_clear_prezeroed(folio))
 		folio_zero_user(folio, addr);
 	/*
 	 * The memory barrier inside __folio_mark_uptodate makes sure that
-- 
MST