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

[Michael S. Tsirkin]

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@xxxxxxxxxx>
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