[PATCH v4 05/15] linux/mm.h: move section functions to mm/page_section.h

[Max Kellermann]

Prepare to reduce dependencies on linux/mm.h.

page_to_section() is used by __page_to_pfn() (but
asm-generic/memory_model.h does not include linux/mm.h).  Thus, in
order to be able to use anything that calls page_to_pfn(), linux/mm.h
needs to be included.

This would prevent us from moving page_address() to a separate header,
because it calls lowmem_page_address() which in turn calls
page_to_virt() and then page_to_pfn().  To prepare for this move, we
move page_to_section() out of linux/mm.h into a separate lean header.

Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
---
 include/linux/mm.h              | 18 +-----------------
 include/linux/mm/page_section.h | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+), 17 deletions(-)
 create mode 100644 include/linux/mm/page_section.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e140ee45f49c..79c1f924d4b5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3,6 +3,7 @@
 #define _LINUX_MM_H
 
 #include <linux/mm/page_kasan_tag.h>
+#include <linux/mm/page_section.h>
 #include <linux/errno.h>
 #include <linux/mmdebug.h>
 #include <linux/gfp.h>
@@ -1637,10 +1638,6 @@ static inline bool is_nommu_shared_mapping(vm_flags_t flags)
 }
 #endif
 
-#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
-#define SECTION_IN_PAGE_FLAGS
-#endif
-
 /*
  * The identification function is mainly used by the buddy allocator for
  * determining if two pages could be buddies. We are not really identifying
@@ -1838,19 +1835,6 @@ static inline pg_data_t *folio_pgdat(const struct folio *folio)
 	return page_pgdat(&folio->page);
 }
 
-#ifdef SECTION_IN_PAGE_FLAGS
-static inline void set_page_section(struct page *page, unsigned long section)
-{
-	page->flags &= ~(SECTIONS_MASK << SECTIONS_PGSHIFT);
-	page->flags |= (section & SECTIONS_MASK) << SECTIONS_PGSHIFT;
-}
-
-static inline unsigned long page_to_section(const struct page *page)
-{
-	return (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
-}
-#endif
-
 /**
  * folio_pfn - Return the Page Frame Number of a folio.
  * @folio: The folio.
diff --git a/include/linux/mm/page_section.h b/include/linux/mm/page_section.h
new file mode 100644
index 000000000000..e4558c2691b8
--- /dev/null
+++ b/include/linux/mm/page_section.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MM_PAGE_SECTION_H
+#define _LINUX_MM_PAGE_SECTION_H
+
+#include <linux/mm_types.h> // for struct page
+#include <linux/mmzone.h> // for SECTIONS_*
+
+#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
+#define SECTION_IN_PAGE_FLAGS
+
+static inline void set_page_section(struct page *page, unsigned long section)
+{
+	page->flags &= ~(SECTIONS_MASK << SECTIONS_PGSHIFT);
+	page->flags |= (section & SECTIONS_MASK) << SECTIONS_PGSHIFT;
+}
+
+static inline unsigned long page_to_section(const struct page *page)
+{
+	return (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
+}
+#endif
+
+#endif /* _LINUX_MM_PAGE_SECTION_H */
-- 
2.39.2