[PATCH RFC v3 07/19] mm: use __GFP_ZERO in vma_alloc_anon_folio_pmd

Michael S. Tsirkin
2026-04-21T22:01:46Z

Convert vma_alloc_anon_folio_pmd() to pass __GFP_ZERO instead of
zeroing at the callsite.

Pass the exact fault address (not PMD-aligned) to vma_alloc_folio()
to ensure the cache locality optimization in folio_zero_user()
works correctly. The NUMA interleave index computation already
shifts by PAGE_SHIFT + order, so the unmasked address gives the
same result.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
mm/huge_memory.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8e2746ea74ad..3f2a868cf9e9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1256,11 +1256,11 @@ EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
unsigned long addr)
{
- gfp_t gfp = vma_thp_gfp_mask(vma);
+ gfp_t gfp = vma_thp_gfp_mask(vma) | __GFP_ZERO;
const int order = HPAGE_PMD_ORDER;
struct folio *folio;

- folio = vma_alloc_folio(gfp, order, vma, addr & HPAGE_PMD_MASK);
+ folio = vma_alloc_folio(gfp, order, vma, addr);

if (unlikely(!folio)) {
count_vm_event(THP_FAULT_FALLBACK);
@@ -1279,14 +1279,6 @@ 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())
- folio_zero_user(folio, addr);
/*
* The memory barrier inside __folio_mark_uptodate makes sure that
* folio_zero_user writes become visible before the set_pmd_at()
--
MST