[PATCH v3 4/4] mm: Mark pages in use for page tables

[Matthew Wilcox <willy@infradead.org>]

From: Matthew Wilcox <mawilcox@microsoft.com>

Define a new PageTable bit in the page_type and use it to mark pages in
use as page tables.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
 include/linux/mm.h         | 2 ++
 include/linux/page-flags.h | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..7a15042d6828 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1829,6 +1829,7 @@ static inline bool pgtable_page_ctor(struct page *page)
 {
 	if (!ptlock_init(page))
 		return false;
+	__SetPageTable(page);
 	inc_zone_page_state(page, NR_PAGETABLE);
 	return true;
 }
@@ -1836,6 +1837,7 @@ static inline bool pgtable_page_ctor(struct page *page)
 static inline void pgtable_page_dtor(struct page *page)
 {
 	pte_lock_deinit(page);
+	__ClearPageTable(page);
 	dec_zone_page_state(page, NR_PAGETABLE);
 }
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 8142ab716e90..ac6bab90849c 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -644,6 +644,7 @@ PAGEFLAG_FALSE(DoubleMap)
 #define PG_balloon	0x00000100
 #define PG_kmemcg	0x00000200
 #define PG_vmalloc	0x00000400
+#define PG_table	0x00000800
 
 #define PageType(page, flag)						\
 	((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
@@ -687,6 +688,11 @@ PAGE_TYPE_OPS(Kmemcg, kmemcg)
  */
 PAGE_TYPE_OPS(Vmalloc, vmalloc)
 
+/*
+ * Marks pages in use as page tables.
+ */
+PAGE_TYPE_OPS(Table, table)
+
 extern bool is_free_buddy_page(struct page *page);
 
 __PAGEFLAG(Isolated, isolated, PF_ANY);
-- 
2.16.1

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