+ mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/sparse-vmemmap: move vmemmap optimization helpers to a public header
has been added to the -mm mm-unstable branch.  Its filename is
     mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Muchun Song <muchun.song@linux.dev>
Subject: mm/sparse-vmemmap: move vmemmap optimization helpers to a public header
Date: Sun, 27 Sep 2026 10:54:37 +0800

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.

Link: https://lore.kernel.org/20260927025441.741633-9-songmuchun@bytedance.com
Signed-off-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <chleroy@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Lance Yang <lance.yang@linux.dev>
---

 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(-)

--- a/arch/loongarch/include/asm/pgtable.h~mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header
+++ a/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>
 
--- a/arch/riscv/mm/init.c~mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header
+++ a/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>
--- a/include/linux/mmzone.h~mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header
+++ a/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 a/include/linux/vmemmap-optimization.h
new file mode 100644
--- /dev/null
+++ a/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 */
--- a/MAINTAINERS~mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header
+++ a/MAINTAINERS
@@ -12096,6 +12096,7 @@ 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
--- a/mm/hugetlb.c~mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header
+++ a/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)
--- a/mm/hugetlb_vmemmap.c~mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header
+++ a/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
--- a/mm/sparse.h~mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header
+++ a/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(
  * 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);
_

Patches currently in -mm which might be from muchun.song@linux.dev are

mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.patch
mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.patch
mm-sparse-vmemmap-introduce-config_vmemmap_optimization.patch
mm-sparse-vmemmap-open-code-init_compound_tail.patch
mm-sparse-vmemmap-prepare-dax-vmemmap-population-for-compound-page-orders.patch
mm-sparse-vmemmap-set-compound-page-order-for-device-dax.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch
powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch
mm-sparse-vmemmap-drop-unused-section_nr_vmemmap_pages-arguments.patch
documentation-mm-update-dax-vmemmap-deduplication-docs.patch