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

Michael S. Tsirkin
2026-04-20T12:51:09Z

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@redhat.com>
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