[PATCH v6 08/12] mm/sparse-vmemmap: move vmemmap optimization helpers to a public header

COLD24d LANDED: 3 (3M)

From: Muchun Song <hidden>
Date: 2026-09-30 14:08:27
Also in: linux-doc, linux-mm, lkml
Subsystem: hugetlb subsystem, loongarch, memory management, memory management - core, memory management - mglru (multi-gen lru), risc-v architecture, the rest · Maintainers: Muchun Song, Oscar Salvador, Huacai Chen, Andrew Morton, David Hildenbrand, Paul Walmsley, Palmer Dabbelt, Albert Ou, Linus Torvalds

Revision v6 of 6 in this series; 3 review trailers (3 from subsystem maintainers); landed in mainline as d3a699634c2a on 2026-10-09.

Revisions (6)

2026-08-31 v1 [diff vs current]
2026-09-08 v2 [diff vs current]
2026-09-11 v3 [diff vs current]
2026-09-16 v4 [diff vs current]
2026-09-27 v5 [diff vs current]
2026-09-30 v6 current

The vmemmap optimization helpers currently live in mm/sparse.h,
which is an internal MM header. That works for MM code, but
prevents powerpc from using the same interfaces without including a
private header.

Move the declarations and inline helpers to vmemmap-optimization.h.
This is a preparatory change for powerpc, which has its own vmemmap
optimization implementation and needs to use the common vmemmap
optimization interfaces from architecture code.

Signed-off-by: Muchun Song <redacted>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
---
v6:
- Collect Acked-by from David Hildenbrand

v5:
- Move the VMEMMAP_OPTIMIZATION_* macros and MAX_FOLIO_VMEMMAP_ALIGN to
  vmemmap-optimization.h

v4:
- Use the renamed VMEMMAP_OPTIMIZATION config in the public header
- Collect Acked-by from Mike Rapoport

v3:
- Update the subject and commit message to describe common vmemmap
  optimization helpers
- Collect Acked-by from Qi Zheng

v2:
- Fix missing header dependencies.
---
 MAINTAINERS                          |   1 +
 arch/loongarch/include/asm/pgtable.h |   1 +
 arch/riscv/mm/init.c                 |   1 +
 include/linux/mmzone.h               |  17 -----
 include/linux/vmemmap-optimization.h | 109 +++++++++++++++++++++++++++
 mm/hugetlb.c                         |   2 +-
 mm/hugetlb_vmemmap.c                 |   2 +-
 mm/sparse.h                          |  78 +------------------
 8 files changed, 115 insertions(+), 96 deletions(-)
 create mode 100644 include/linux/vmemmap-optimization.h

diff --git a/MAINTAINERS b/MAINTAINERS
index fe1d70ed5100..4689a0210060 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -12097,6 +12097,7 @@ F:	Documentation/mm/hugetlbfs_reserv.rst
 F:	Documentation/mm/vmemmap_dedup.rst
 F:	fs/hugetlbfs/
 F:	include/linux/hugetlb.h
+F:	include/linux/vmemmap-optimization.h
 F:	include/trace/events/hugetlbfs.h
 F:	mm/hugetlb.c
 F:	mm/hugetlb_cgroup.c

diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index cf29a4c8ac59..f87603135131 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h

@@ -72,6 +72,7 @@
 
 #include <linux/mm_types.h>
 #include <linux/mmzone.h>
+#include <linux/vmemmap-optimization.h>
 #include <asm/fixmap.h>
 #include <asm/sparsemem.h>

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index fb37b0b67efe..857f9a55039c 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c

@@ -22,6 +22,7 @@
 #include <linux/hugetlb.h>
 #include <linux/kfence.h>
 #include <linux/execmem.h>
+#include <linux/vmemmap-optimization.h>
 
 #include <asm/alternative.h>
 #include <asm/fixmap.h>

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index cd68c1904c91..65de3bb13eb3 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h

@@ -96,23 +96,6 @@
 
 #define MAX_FOLIO_NR_PAGES	(1UL << MAX_FOLIO_ORDER)
 
-/*
- * HugeTLB Vmemmap Optimization (HVO) requires struct pages of the head page to
- * be naturally aligned with regard to the folio size.
- *
- * HVO which is only active if the size of struct page is a power of 2.
- */
-#define MAX_FOLIO_VMEMMAP_ALIGN					\
-	(IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION) &&		\
-	 is_power_of_2(sizeof(struct page)) ?			\
-	 MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
-
-/* The number of retained vmemmap pages with HVO enabled. */
-#define VMEMMAP_OPTIMIZATION_PAGES		1
-#define VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES	\
-	(VMEMMAP_OPTIMIZATION_PAGES * PAGE_SIZE / sizeof(struct page))
-#define VMEMMAP_OPTIMIZATION_MIN_ORDER		(ilog2(VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) + 1)
-
 enum migratetype {
 	MIGRATE_UNMOVABLE,
 	MIGRATE_MOVABLE,

diff --git a/include/linux/vmemmap-optimization.h b/include/linux/vmemmap-optimization.h
new file mode 100644
index 000000000000..bd0974b262a4
--- /dev/null
+++ b/include/linux/vmemmap-optimization.h

@@ -0,0 +1,109 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * vmemmap-optimization.h
+ *
+ * Generic vmemmap optimization declarations.
+ *
+ * Author: Muchun Song <songmuchun@bytedance.com>
+ */
+#ifndef _LINUX_VMEMMAP_OPTIMIZATION_H
+#define _LINUX_VMEMMAP_OPTIMIZATION_H
+
+#include <linux/align.h>
+#include <linux/log2.h>
+#include <linux/mmdebug.h>
+#include <linux/mmzone.h>
+
+/*
+ * HugeTLB Vmemmap Optimization (HVO) requires struct pages of the head page to
+ * be naturally aligned with regard to the folio size.
+ *
+ * HVO which is only active if the size of struct page is a power of 2.
+ */
+#define MAX_FOLIO_VMEMMAP_ALIGN					\
+	(IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION) &&		\
+	 is_power_of_2(sizeof(struct page)) ?			\
+	 MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
+
+/* The number of retained vmemmap pages with HVO enabled. */
+#define VMEMMAP_OPTIMIZATION_PAGES		1
+#define VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES	\
+	(VMEMMAP_OPTIMIZATION_PAGES * PAGE_SIZE / sizeof(struct page))
+#define VMEMMAP_OPTIMIZATION_MIN_ORDER		(ilog2(VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) + 1)
+
+#ifdef CONFIG_VMEMMAP_OPTIMIZATION
+static inline unsigned int section_compound_order(const struct mem_section *section)
+{
+	return section->compound_page_order;
+}
+
+static inline void section_set_compound_order(struct mem_section *section,
+					      unsigned int order)
+{
+	VM_WARN_ON(section_compound_order(section) && order &&
+		   section_compound_order(section) != order);
+	section->compound_page_order = order;
+}
+
+static inline void section_set_compound_order_range(unsigned long pfn,
+		unsigned long nr_pages, unsigned int order)
+{
+	unsigned long section_nr = pfn_to_section_nr(pfn);
+
+	if (!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION))
+		return;
+
+	for (unsigned long i = 0; i < nr_pages / PAGES_PER_SECTION; i++)
+		section_set_compound_order(__nr_to_section(section_nr + i), order);
+}
+
+static inline unsigned int pfn_to_section_compound_order(unsigned long pfn)
+{
+	return section_compound_order(__pfn_to_section(pfn));
+}
+
+struct page *vmemmap_shared_tail_page(unsigned int order, struct zone *zone);
+#else
+static inline unsigned int section_compound_order(const struct mem_section *section)
+{
+	return 0;
+}
+
+static inline void section_set_compound_order(struct mem_section *section,
+					      unsigned int order)
+{
+}
+
+static inline void section_set_compound_order_range(unsigned long pfn,
+		unsigned long nr_pages, unsigned int order)
+{
+}
+
+static inline unsigned int pfn_to_section_compound_order(unsigned long pfn)
+{
+	return 0;
+}
+#endif /* CONFIG_VMEMMAP_OPTIMIZATION */
+
+static inline bool vmemmap_optimizable_pfn(unsigned long pfn)
+{
+	const unsigned int order = pfn_to_section_compound_order(pfn);
+	const unsigned long nr_pages = 1UL << order;
+
+	if (!is_power_of_2(sizeof(struct page)))
+		return false;
+
+	return (pfn & (nr_pages - 1)) >= VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES;
+}
+
+static inline bool vmemmap_optimizable_order(unsigned int order)
+{
+	if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
+		return false;
+
+	if (!is_power_of_2(sizeof(struct page)))
+		return false;
+
+	return order >= VMEMMAP_OPTIMIZATION_MIN_ORDER;
+}
+#endif /* _LINUX_VMEMMAP_OPTIMIZATION_H */

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index fd00141b089a..2003439ea13c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c

@@ -38,6 +38,7 @@
 #include <linux/mm_inline.h>
 #include <linux/padata.h>
 #include <linux/pgalloc.h>
+#include <linux/vmemmap-optimization.h>
 
 #include <asm/page.h>
 #include <asm/tlb.h>

@@ -52,7 +53,6 @@
 #include "hugetlb_cma.h"
 #include "hugetlb_internal.h"
 #include "mm_init.h"
-#include "sparse.h"
 #include <linux/page-isolation.h>
 
 #define HUGE_BOOTMEM_ZONES_VALID	BIT(0)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 76765c97ff68..0057fa2a16a8 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c

@@ -15,10 +15,10 @@
 #include <linux/mmdebug.h>
 #include <linux/pagewalk.h>
 #include <linux/pgalloc.h>
+#include <linux/vmemmap-optimization.h>
 
 #include <asm/tlbflush.h>
 #include "hugetlb_vmemmap.h"
-#include "sparse.h"
 
 /**
  * struct vmemmap_remap_walk - walk vmemmap page table

diff --git a/mm/sparse.h b/mm/sparse.h
index 326ad43bb5c3..a5111087ee3a 100644
--- a/mm/sparse.h
+++ b/mm/sparse.h

@@ -9,80 +9,7 @@
 #define __MM_SPARSE_H
 
 #include <linux/mmzone.h>
-
-#ifdef CONFIG_VMEMMAP_OPTIMIZATION
-static inline unsigned int section_compound_order(const struct mem_section *section)
-{
-	return section->compound_page_order;
-}
-
-static inline void section_set_compound_order(struct mem_section *section,
-					      unsigned int order)
-{
-	VM_WARN_ON(section_compound_order(section) && order &&
-		   section_compound_order(section) != order);
-	section->compound_page_order = order;
-}
-
-static inline void section_set_compound_order_range(unsigned long pfn,
-		unsigned long nr_pages, unsigned int order)
-{
-	unsigned long section_nr = pfn_to_section_nr(pfn);
-
-	if (!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION))
-		return;
-
-	for (unsigned long i = 0; i < nr_pages / PAGES_PER_SECTION; i++)
-		section_set_compound_order(__nr_to_section(section_nr + i), order);
-}
-
-static inline unsigned int pfn_to_section_compound_order(unsigned long pfn)
-{
-	return section_compound_order(__pfn_to_section(pfn));
-}
-#else
-static inline unsigned int section_compound_order(const struct mem_section *section)
-{
-	return 0;
-}
-
-static inline void section_set_compound_order(struct mem_section *section,
-					      unsigned int order)
-{
-}
-
-static inline void section_set_compound_order_range(unsigned long pfn,
-		unsigned long nr_pages, unsigned int order)
-{
-}
-
-static inline unsigned int pfn_to_section_compound_order(unsigned long pfn)
-{
-	return 0;
-}
-#endif
-
-static inline bool vmemmap_optimizable_pfn(unsigned long pfn)
-{
-	const unsigned int order = pfn_to_section_compound_order(pfn);
-	const unsigned long nr_pages = 1UL << order;
-
-	if (!is_power_of_2(sizeof(struct page)))
-		return false;
-
-	return (pfn & (nr_pages - 1)) >= VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES;
-}
-
-static inline bool vmemmap_optimizable_order(unsigned int order)
-{
-	if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
-		return false;
-
-	if (!is_power_of_2(sizeof(struct page)))
-		return false;
-
-	return order >= VMEMMAP_OPTIMIZATION_MIN_ORDER;
-}
+#include <linux/vmemmap-optimization.h>
 
 /*
  * mm/sparse.c

@@ -142,9 +69,6 @@ static inline void sparse_sections_init(void) {}
  * mm/sparse-vmemmap.c
  */
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
-#ifdef CONFIG_VMEMMAP_OPTIMIZATION
-struct page *vmemmap_shared_tail_page(unsigned int order, struct zone *zone);
-#endif
 void sparse_init_subsection_map(void);
 int section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
 		struct vmem_altmap *altmap, struct dev_pagemap *pgmap);

-- 
2.54.0

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