bootmem: stop using page->index

Encode the type into the bottom four bits of page->private and the info
into the remaining bits.  Also turn the bootmem type into a named enum.

[arnd@arndb.de: bootmem: add bootmem_type stub function]
  Link: https://lkml.kernel.org/r/20241015143802.577613-1-arnd@kernel.org
[akpm@linux-foundation.org: fix build with !CONFIG_HAVE_BOOTMEM_INFO_NODE]
 Link: https://lore.kernel.org/oe-kbuild-all/202410090311.eaqcL7IZ-lkp@intel.com/
Link: https://lkml.kernel.org/r/20241005200121.3231142-6-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: kernel test robot <lkp@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Matthew Wilcox (Oracle)

arch/x86/mm/init_64.c

@@ -985,22 +985,32 @@ int arch_add_memory(int nid, u64 start, u64 size,
 	return add_pages(nid, start_pfn, nr_pages, params);
 }
 
-static void __meminit free_pagetable(struct page *page, int order)
+static void free_reserved_pages(struct page *page, unsigned long nr_pages)
 {
-	unsigned long magic;
-	unsigned int nr_pages = 1 << order;
+	while (nr_pages--)
+		free_reserved_page(page++);
+}
 
+static void __meminit free_pagetable(struct page *page, int order)
+{
 	/* bootmem page has reserved flag */
 	if (PageReserved(page)) {
-		magic = page->index;
-		if (magic == SECTION_INFO || magic == MIX_SECTION_INFO) {
+		unsigned long nr_pages = 1 << order;
+#ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
+		enum bootmem_type type = bootmem_type(page);
+
+		if (type == SECTION_INFO || type == MIX_SECTION_INFO) {
 			while (nr_pages--)
 				put_page_bootmem(page++);
-		} else
-			while (nr_pages--)
-				free_reserved_page(page++);
-	} else
+		} else {
+			free_reserved_pages(page, nr_pages);
+		}
+#else
+		free_reserved_pages(page, nr_pages);
+#endif
+	} else {
 		free_pages((unsigned long)page_address(page), order);
+	}
 }
 
 static void __meminit free_hugepage_table(struct page *page,

include/linux/bootmem_info.h

@@ -6,11 +6,10 @@
 #include <linux/kmemleak.h>
 
 /*
- * Types for free bootmem stored in page->lru.next. These have to be in
- * some random range in unsigned long space for debugging purposes.
+ * Types for free bootmem stored in the low bits of page->private.
  */
-enum {
-	MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE = 12,
+enum bootmem_type {
+	MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE = 1,
 	SECTION_INFO = MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE,
 	MIX_SECTION_INFO,
 	NODE_INFO,
@@ -21,25 +20,35 @@ enum {
 void __init register_page_bootmem_info_node(struct pglist_data *pgdat);
 
 void get_page_bootmem(unsigned long info, struct page *page,
-		      unsigned long type);
+		enum bootmem_type type);
 void put_page_bootmem(struct page *page);
 
+static inline enum bootmem_type bootmem_type(const struct page *page)
+{
+	return (unsigned long)page->private & 0xf;
+}
+
+static inline unsigned long bootmem_info(const struct page *page)
+{
+	return (unsigned long)page->private >> 4;
+}
+
 /*
  * Any memory allocated via the memblock allocator and not via the
  * buddy will be marked reserved already in the memmap. For those
  * pages, we can call this function to free it to buddy allocator.
  */
 static inline void free_bootmem_page(struct page *page)
 {
-	unsigned long magic = page->index;
+	enum bootmem_type type = bootmem_type(page);
 
 	/*
 	 * The reserve_bootmem_region sets the reserved flag on bootmem
 	 * pages.
 	 */
 	VM_BUG_ON_PAGE(page_ref_count(page) != 2, page);
 
-	if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
+	if (type == SECTION_INFO || type == MIX_SECTION_INFO)
 		put_page_bootmem(page);
 	else
 		VM_BUG_ON_PAGE(1, page);
@@ -53,8 +62,18 @@ static inline void put_page_bootmem(struct page *page)
 {
 }
 
+static inline enum bootmem_type bootmem_type(const struct page *page)
+{
+	return SECTION_INFO;
+}
+
+static inline unsigned long bootmem_info(const struct page *page)
+{
+	return 0;
+}
+
 static inline void get_page_bootmem(unsigned long info, struct page *page,
-				    unsigned long type)
+				    enum bootmem_type type)
 {
 }
 

mm/bootmem_info.c

@@ -14,23 +14,24 @@
 #include <linux/memory_hotplug.h>
 #include <linux/kmemleak.h>
 
-void get_page_bootmem(unsigned long info, struct page *page, unsigned long type)
+void get_page_bootmem(unsigned long info, struct page *page,
+		enum bootmem_type type)
 {
-	page->index = type;
+	BUG_ON(type > 0xf);
+	BUG_ON(info > (ULONG_MAX >> 4));
 	SetPagePrivate(page);
-	set_page_private(page, info);
+	set_page_private(page, info << 4 | type);
 	page_ref_inc(page);
 }
 
 void put_page_bootmem(struct page *page)
 {
-	unsigned long type = page->index;
+	enum bootmem_type type = bootmem_type(page);
 
 	BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
 	       type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);
 
 	if (page_ref_dec_return(page) == 1) {
-		page->index = 0;
 		ClearPagePrivate(page);
 		set_page_private(page, 0);
 		INIT_LIST_HEAD(&page->lru);

mm/sparse.c

@@ -720,19 +720,19 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
 static void free_map_bootmem(struct page *memmap)
 {
 	unsigned long maps_section_nr, removing_section_nr, i;
-	unsigned long magic, nr_pages;
+	unsigned long type, nr_pages;
 	struct page *page = virt_to_page(memmap);
 
 	nr_pages = PAGE_ALIGN(PAGES_PER_SECTION * sizeof(struct page))
 		>> PAGE_SHIFT;
 
 	for (i = 0; i < nr_pages; i++, page++) {
-		magic = page->index;
+		type = bootmem_type(page);
 
-		BUG_ON(magic == NODE_INFO);
+		BUG_ON(type == NODE_INFO);
 
 		maps_section_nr = pfn_to_section_nr(page_to_pfn(page));
-		removing_section_nr = page_private(page);
+		removing_section_nr = bootmem_info(page);
 
 		/*
 		 * When this function is called, the removing section is