[PATCH RFC 7/9] mm: hugetlb: skip zeroing of pre-zeroed hugetlb pages

[Michael S. Tsirkin]

When a surplus hugetlb page is allocated from the buddy allocator
and the page was previously reported to the host (and zeroed on
reclaim), skip the redundant folio_zero_user() in the hugetlb
fault path.

This only benefits surplus hugetlb pages that are freshly allocated
from the buddy.  Pages from the persistent hugetlb pool are not
affected since they are not allocated from buddy at fault time.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
---
 fs/hugetlbfs/inode.c    | 3 ++-
 include/linux/hugetlb.h | 2 +-
 mm/hugetlb.c            | 3 ++-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 3f70c47981de..301567ad160f 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -828,7 +828,8 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
 			error = PTR_ERR(folio);
 			goto out;
 		}
-		folio_zero_user(folio, addr);
+		if (!folio_test_clear_prezeroed(folio))
+			folio_zero_user(folio, addr);
 		__folio_mark_uptodate(folio);
 		error = hugetlb_add_to_page_cache(folio, mapping, index);
 		if (unlikely(error)) {
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 65910437be1c..07e3ef8c0418 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -937,7 +937,7 @@ static inline bool hugepage_movable_supported(struct hstate *h)
 /* Movability of hugepages depends on migration support. */
 static inline gfp_t htlb_alloc_mask(struct hstate *h)
 {
-	gfp_t gfp = __GFP_COMP | __GFP_NOWARN;
+	gfp_t gfp = __GFP_COMP | __GFP_NOWARN | __GFP_PREZEROED;
 
 	gfp |= hugepage_movable_supported(h) ? GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER;
 
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0beb6e22bc26..5b23b006c37c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5809,7 +5809,8 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
 				ret = 0;
 			goto out;
 		}
-		folio_zero_user(folio, vmf->real_address);
+		if (!folio_test_clear_prezeroed(folio))
+			folio_zero_user(folio, vmf->real_address);
 		__folio_mark_uptodate(folio);
 		new_folio = true;
 
-- 
MST