[PATCH 20/49] mm: rename vmemmap optimization macros to generic names

[Muchun Song]

In preparation for unifying the vmemmap optimization paths for both
DAX and HugeTLB, rename the existing vmemmap tail page macros to
more generic, semantic-based names.

The original names (e.g., VMEMMAP_TAIL_MIN_ORDER) fail to clearly express
the actual requirement: it represents the minimum order of a folio that
can satisfy the vmemmap optimization. To provide a broader and clearer
abstraction for other users like DAX, replace them with newly introduced
macros like OPTIMIZABLE_FOLIO_MIN_ORDER and NR_OPTIMIZABLE_FOLIO_SIZES.

These new macros, along with OPTIMIZED_FOLIO_VMEMMAP_PAGES,
OPTIMIZED_FOLIO_VMEMMAP_SIZE, and OPTIMIZED_FOLIO_VMEMMAP_PAGE_STRUCTS,
are explicitly bound to the 'folio' concept. This systematic naming
makes it clearer to describe the properties of a vmemmap-optimized
folio rather than just raw pages.

Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
 include/linux/mmzone.h | 18 ++++++++++--------
 mm/hugetlb_vmemmap.c   |  6 +++---
 mm/sparse-vmemmap.c    |  4 ++--
 3 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 8ee9dc60120a..378feaf4e4ed 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -107,13 +107,15 @@
 	 is_power_of_2(sizeof(struct page)) ? \
 	 MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
 
-/*
- * vmemmap optimization (like HVO) is only possible for page orders that fill
- * two or more pages with struct pages.
- */
-#define VMEMMAP_TAIL_MIN_ORDER (ilog2(2 * PAGE_SIZE / sizeof(struct page)))
-#define __NR_VMEMMAP_TAILS (MAX_FOLIO_ORDER - VMEMMAP_TAIL_MIN_ORDER + 1)
-#define NR_VMEMMAP_TAILS (__NR_VMEMMAP_TAILS > 0 ? __NR_VMEMMAP_TAILS : 0)
+/* The number of vmemmap pages required by a vmemmap-optimized folio. */
+#define OPTIMIZED_FOLIO_VMEMMAP_PAGES		1
+#define OPTIMIZED_FOLIO_VMEMMAP_SIZE		(OPTIMIZED_FOLIO_VMEMMAP_PAGES * PAGE_SIZE)
+#define OPTIMIZED_FOLIO_VMEMMAP_PAGE_STRUCTS	(OPTIMIZED_FOLIO_VMEMMAP_SIZE / sizeof(struct page))
+#define OPTIMIZABLE_FOLIO_MIN_ORDER		(ilog2(OPTIMIZED_FOLIO_VMEMMAP_PAGE_STRUCTS) + 1)
+
+#define __NR_OPTIMIZABLE_FOLIO_SIZES		(MAX_FOLIO_ORDER - OPTIMIZABLE_FOLIO_MIN_ORDER + 1)
+#define NR_OPTIMIZABLE_FOLIO_SIZES		\
+	(__NR_OPTIMIZABLE_FOLIO_SIZES > 0 ? __NR_OPTIMIZABLE_FOLIO_SIZES : 0)
 
 enum migratetype {
 	MIGRATE_UNMOVABLE,
@@ -1144,7 +1146,7 @@ struct zone {
 	atomic_long_t		vm_stat[NR_VM_ZONE_STAT_ITEMS];
 	atomic_long_t		vm_numa_event[NR_VM_NUMA_EVENT_ITEMS];
 #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-	struct page *vmemmap_tails[NR_VMEMMAP_TAILS];
+	struct page *vmemmap_tails[NR_OPTIMIZABLE_FOLIO_SIZES];
 #endif
 } ____cacheline_internodealigned_in_smp;
 
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 535f0369a496..d6dd47c232e0 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -495,7 +495,7 @@ static bool vmemmap_should_optimize_folio(const struct hstate *h, struct folio *
 
 static struct page *vmemmap_get_tail(unsigned int order, struct zone *zone)
 {
-	const unsigned int idx = order - VMEMMAP_TAIL_MIN_ORDER;
+	const unsigned int idx = order - OPTIMIZABLE_FOLIO_MIN_ORDER;
 	struct page *tail, *p;
 	int node = zone_to_nid(zone);
 
@@ -828,7 +828,7 @@ static int __init hugetlb_vmemmap_init(void)
 	BUILD_BUG_ON(__NR_USED_SUBPAGE > HUGETLB_VMEMMAP_RESERVE_PAGES);
 
 	for_each_zone(zone) {
-		for (int i = 0; i < NR_VMEMMAP_TAILS; i++) {
+		for (int i = 0; i < NR_OPTIMIZABLE_FOLIO_SIZES; i++) {
 			struct page *tail, *p;
 			unsigned int order;
 
@@ -836,7 +836,7 @@ static int __init hugetlb_vmemmap_init(void)
 			if (!tail)
 				continue;
 
-			order = i + VMEMMAP_TAIL_MIN_ORDER;
+			order = i + OPTIMIZABLE_FOLIO_MIN_ORDER;
 			p = page_to_virt(tail);
 			for (int j = 0; j < PAGE_SIZE / sizeof(struct page); j++)
 				init_compound_tail(p + j, NULL, order, zone);
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 3fdb6808e8ab..9f70559df4e8 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -330,12 +330,12 @@ static __meminit struct page *vmemmap_get_tail(unsigned int order, struct zone *
 	unsigned int idx;
 	int node = zone_to_nid(zone);
 
-	if (WARN_ON_ONCE(order < VMEMMAP_TAIL_MIN_ORDER))
+	if (WARN_ON_ONCE(order < OPTIMIZABLE_FOLIO_MIN_ORDER))
 		return NULL;
 	if (WARN_ON_ONCE(order > MAX_FOLIO_ORDER))
 		return NULL;
 
-	idx = order - VMEMMAP_TAIL_MIN_ORDER;
+	idx = order - OPTIMIZABLE_FOLIO_MIN_ORDER;
 	tail = zone->vmemmap_tails[idx];
 	if (tail)
 		return tail;
-- 
2.20.1