[PATCH RFC v2 14/18] mm: memfd: skip zeroing for pre-zeroed hugetlb pages

[Michael S. Tsirkin]

Use the pghint_t output from alloc_hugetlb_folio_reserve() to
skip folio_zero_user() 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/memfd.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/mm/memfd.c b/mm/memfd.c
index f1c00600e19a..546149897369 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -81,6 +81,7 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
 		struct hstate *h = hstate_file(memfd);
 		int err = -ENOMEM;
 		long nr_resv;
+		pghint_t hints;
 
 		gfp_mask = htlb_alloc_mask(h);
 		gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
@@ -93,17 +94,12 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
 		folio = alloc_hugetlb_folio_reserve(h,
 						    numa_node_id(),
 						    NULL,
-						    gfp_mask, NULL);
+						    gfp_mask, &hints);
 		if (folio) {
 			u32 hash;
 
-			/*
-			 * Zero the folio to prevent information leaks to userspace.
-			 * Use folio_zero_user() which is optimized for huge/gigantic
-			 * pages. Pass 0 as addr_hint since this is not a faulting path
-			 *  and we don't have a user virtual address yet.
-			 */
-			folio_zero_user(folio, 0);
+			if (!(hints & PGHINT_ZEROED))
+				folio_zero_user(folio, 0);
 
 			/*
 			 * Mark the folio uptodate before adding to page cache,
-- 
MST