mm: add hmm_data to struct page

Make hmm_data an explicit member of the struct page union.

Link: http://lkml.kernel.org/r/20180518194519.3820-14-willy@infradead.orgSigned-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/hmm.h

@@ -522,9 +522,7 @@ void hmm_devmem_remove(struct hmm_devmem *devmem);
 static inline void hmm_devmem_page_set_drvdata(struct page *page,
 					       unsigned long data)
 {
-	unsigned long *drvdata = (unsigned long *)&page->pgmap;
-
-	drvdata[1] = data;
+	page->hmm_data = data;
 }
 
 /*
@@ -535,9 +533,7 @@ static inline void hmm_devmem_page_set_drvdata(struct page *page,
  */
 static inline unsigned long hmm_devmem_page_get_drvdata(const struct page *page)
 {
-	const unsigned long *drvdata = (const unsigned long *)&page->pgmap;
-
-	return drvdata[1];
+	return page->hmm_data;
 }
 
 

include/linux/mm_types.h

@@ -146,15 +146,15 @@ struct page {
 			spinlock_t ptl;
 #endif
 		};
+		struct {	/* ZONE_DEVICE pages */
+			/** @pgmap: Points to the hosting device page map. */
+			struct dev_pagemap *pgmap;
+			unsigned long hmm_data;
+			unsigned long _zd_pad_1;	/* uses mapping */
+		};
 
 		/** @rcu_head: You can use this to free a page by RCU. */
 		struct rcu_head rcu_head;
-
-		/**
-		 * @pgmap: For ZONE_DEVICE pages, this points to the hosting
-		 * device page map.
-		 */
-		struct dev_pagemap *pgmap;
 	};
 
 	union {		/* This union is 4 bytes in size. */