mm: move _refcount out of struct page union

Keeping the refcount in the union only encourages people to put something
else in the union which will overlap with _refcount and eventually explode
messily.  pahole reports no fields change location.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Jérôme Glisse <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 10 insertions, 15 deletions

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index bcc5ee8b7b07..0b0c0e224011 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -113,7 +113,13 @@ struct page {
 		};
 	};
 
-	union {
+	union {		/* This union is 4 bytes in size. */
+		/*
+		 * If the page can be mapped to userspace, encodes the number
+		 * of times this page is referenced by a page table.
+		 */
+		atomic_t _mapcount;
+
 		/*
 		 * If the page is neither PageSlab nor mappable to userspace,
 		 * the value stored here may help determine what this page
@@ -124,22 +130,11 @@ struct page {
 
 		unsigned int active;		/* SLAB */
 		int units;			/* SLOB */
-
-		struct {			/* Page cache */
-			/*
-			 * Count of ptes mapped in mms, to show when
-			 * page is mapped & limit reverse map searches.
-			 */
-			atomic_t _mapcount;
-
-			/*
-			 * Usage count, *USE WRAPPER FUNCTION* when manual
-			 * accounting. See page_ref.h
-			 */
-			atomic_t _refcount;
-		};
 	};
 
+	/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
+	atomic_t _refcount;
+
 	/*
 	 * WARNING: bit 0 of the first word encode PageTail(). That means
 	 * the rest users of the storage space MUST NOT use the bit to