[PATCH RFC v2 13/18] mm: skip zeroing in vma_alloc_anon_folio_pmd for pre-zeroed pages

[Michael S. Tsirkin]

Use vma_alloc_folio_hints() and check PGHINT_ZEROED 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
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/huge_memory.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b298cba853ab..243592452ead 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1259,8 +1259,10 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 	gfp_t gfp = vma_thp_gfp_mask(vma);
 	const int order = HPAGE_PMD_ORDER;
 	struct folio *folio;
+	pghint_t hints;
 
-	folio = vma_alloc_folio(gfp, order, vma, addr & HPAGE_PMD_MASK);
+	folio = vma_alloc_folio_hints(gfp, order, vma, addr & HPAGE_PMD_MASK,
+				      &hints);
 
 	if (unlikely(!folio)) {
 		count_vm_event(THP_FAULT_FALLBACK);
@@ -1279,13 +1281,7 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 	}
 	folio_throttle_swaprate(folio, gfp);
 
-       /*
-	* When a folio is not zeroed during allocation (__GFP_ZERO not used)
-	* or user folios require special handling, folio_zero_user() is used to
-	* 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() && !(hints & PGHINT_ZEROED))
 		folio_zero_user(folio, addr);
 	/*
 	 * The memory barrier inside __folio_mark_uptodate makes sure that
-- 
MST