[RFC PATCH 2/3] mm: Introduce a new Vmemmap page-type

[Oscar Salvador]

This patch introduces a new Vmemmap page-type so we can better
picture and handle those kind of pages.

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
---
 include/linux/mm.h         | 6 ++++++
 include/linux/mm_types.h   | 5 +++++
 include/linux/page-flags.h | 6 ++++++
 3 files changed, 17 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ef360fe70aaf..48845f054136 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3126,6 +3126,12 @@ static inline bool debug_guardpage_enabled(void) { return false; }
 static inline bool page_is_guard(struct page *page) { return false; }
 #endif /* CONFIG_DEBUG_PAGEALLOC */
 
+static __always_inline unsigned long vmemmap_nr_pages(struct page *page)
+{
+	struct page *head = (struct page *)page->vmemmap_head;
+	return head->vmemmap_pages - (page - head);
+}
+
 #if MAX_NUMNODES > 1
 void __init setup_nr_node_ids(void);
 #else
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ae891c0c55fc..0bb8de4262c3 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -171,6 +171,11 @@ struct page {
 			 * pmem backed DAX files are mapped.
 			 */
 		};
+		struct {	/* Vmemmap pages */
+			unsigned long vmemmap_head;
+			unsigned long vmemmap_sections; /* Number of sections */
+			unsigned long vmemmap_pages;    /* Number of pages */
+		};
 
 		/** @rcu_head: You can use this to free a page by RCU. */
 		struct rcu_head rcu_head;
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 4f6ba9379112..2bad207515fa 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -718,6 +718,7 @@ PAGEFLAG_FALSE(DoubleMap)
 #define PG_kmemcg	0x00000200
 #define PG_table	0x00000400
 #define PG_guard	0x00000800
+#define PG_vmemmap     0x00001000
 
 #define PageType(page, flag)						\
 	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
@@ -784,6 +785,11 @@ PAGE_TYPE_OPS(Table, table)
  */
 PAGE_TYPE_OPS(Guard, guard)
 
+/*
+ * Vmemmap pages (see include/linux/memory_hotplug.h).
+ */
+PAGE_TYPE_OPS(Vmemmap, vmemmap)
+
 extern bool is_free_buddy_page(struct page *page);
 
 __PAGEFLAG(Isolated, isolated, PF_ANY);
-- 
2.26.2