[PATCH RFC v2 12/18] mm: skip zeroing in alloc_anon_folio for pre-zeroed pages

[Michael S. Tsirkin]

Use vma_alloc_folio_hints() and check PGHINT_ZEROED to skip
folio_zero_user() in the mTHP 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/memory.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index c65e82c86fed..066e2c9781dc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5179,8 +5179,10 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 	/* Try allocating the highest of the remaining orders. */
 	gfp = vma_thp_gfp_mask(vma);
 	while (orders) {
+		pghint_t hints;
+
 		addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
-		folio = vma_alloc_folio(gfp, order, vma, addr);
+		folio = vma_alloc_folio_hints(gfp, order, vma, addr, &hints);
 		if (folio) {
 			if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
 				count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
@@ -5188,14 +5190,8 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 				goto next;
 			}
 			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, vmf->address);
 			return folio;
 		}
-- 
MST