[PATCH 10/12] mm: hugetlb_vmemmap: make vmemmap restoration folio-oriented

[Muchun Song]

Like optimization, vmemmap restoration operates on one folio at a time,
but the current interface exposes a raw address range and requires the
HugeTLB caller to prepare part of the operation.  This splits the common
mechanism across layers and obscures its natural unit of work.

Make the folio the unit of vmemmap restoration and move the common
mechanics behind a folio-oriented interface.  This keeps HugeTLB-specific
eligibility and state in the caller and gives both directions of HVO
consistent folio-level interfaces.

No functional change intended.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/hugetlb_vmemmap.c | 37 +++++++++++++------------------------
 1 file changed, 13 insertions(+), 24 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index b76203e34881..97748a9cefe2 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -360,28 +360,29 @@ static int vmemmap_optimize_folio(const struct folio *folio,
 }
 
 /**
- * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
- *			 to the page which is from the @vmemmap_pages
- *			 respectively.
- * @start:	start address of the vmemmap virtual address range that we want
- *		to remap.
- * @end:	end address of the vmemmap virtual address range that we want to
- *		remap.
- * @flags:	modifications to vmemmap_remap_walk flags
+ * vmemmap_restore_folio - restore the vmemmap backing of a folio
+ * @folio:	folio whose vmemmap pages should be restored.
+ * @flags:	vmemmap remap control flags passed to vmemmap_remap_walk.
+ *
+ * Remap @folio's vmemmap so optimizable entries are restored from the shared
+ * tail page back to distinct backing pages allocated for @folio, while
+ * non-optimizable entries remain unchanged.
  *
  * Return: %0 on success, negative error code otherwise.
  */
-static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
-			       unsigned long flags)
+static int vmemmap_restore_folio(const struct folio *folio, unsigned long flags)
 {
 	LIST_HEAD(vmemmap_pages);
-	int nid = page_to_nid((struct page *)start);
+	int nid = folio_nid(folio);
+	unsigned long start = (unsigned long)folio_page(folio, 0);
+	unsigned long end = start + folio_vmemmap_size(folio);
 	struct vmemmap_remap_walk walk = {
 		.remap_pte	= vmemmap_restore_pte,
 		.vmemmap_pages	= &vmemmap_pages,
 		.flags		= flags,
 	};
 
+	start += VMEMMAP_OPTIMIZATION_SIZE;
 	if (alloc_vmemmap_page_list(&vmemmap_pages, (end - start) / PAGE_SIZE, nid))
 		return -ENOMEM;
 
@@ -399,7 +400,6 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
 					   struct folio *folio, unsigned long flags)
 {
 	int ret;
-	unsigned long vmemmap_start, vmemmap_end;
 
 	VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
 	VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
@@ -407,18 +407,7 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
 	if (!folio_test_hugetlb_vmemmap_optimized(folio))
 		return 0;
 
-	vmemmap_start	= (unsigned long)&folio->page;
-	vmemmap_end	= vmemmap_start + hugetlb_vmemmap_size(h);
-
-	vmemmap_start	+= VMEMMAP_OPTIMIZATION_SIZE;
-
-	/*
-	 * The pages which the vmemmap virtual address range [@vmemmap_start,
-	 * @vmemmap_end) are mapped to are freed to the buddy allocator.
-	 * When a HugeTLB page is freed to the buddy allocator, previously
-	 * discarded vmemmap pages must be allocated and remapping.
-	 */
-	ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, flags);
+	ret = vmemmap_restore_folio(folio, flags);
 	if (!ret)
 		folio_clear_hugetlb_vmemmap_optimized(folio);
 
-- 
2.54.0