mm: move 'private' union within struct page

By moving page->private to the fourth word of struct page, we can put the
SLUB counters in the same word as SLAB's s_mem and still do the
cmpxchg_double trick.  Now the SLUB counters no longer overlap with the
mapcount or refcount so we can drop the call to page_mapcount_reset() and
simplify set_page_slub_counters() to a single line.

Link: http://lkml.kernel.org/r/20180518194519.3820-6-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jérôme Glisse <jglisse@redhat.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>

1 files changed, 25 insertions, 31 deletions

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 6f153f2fab504..bcc5ee8b7b073 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -65,15 +65,9 @@ struct hmm;
  */
 #ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
 #define _struct_page_alignment	__aligned(2 * sizeof(unsigned long))
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE)
-#define _slub_counter_t		unsigned long
 #else
-#define _slub_counter_t		unsigned int
-#endif
-#else /* !CONFIG_HAVE_ALIGNED_STRUCT_PAGE */
 #define _struct_page_alignment
-#define _slub_counter_t		unsigned int
-#endif /* !CONFIG_HAVE_ALIGNED_STRUCT_PAGE */
+#endif
 
 struct page {
 	/* First double word block */
@@ -97,6 +91,30 @@ struct page {
 
 	union {
 		/*
+		 * Mapping-private opaque data:
+		 * Usually used for buffer_heads if PagePrivate
+		 * Used for swp_entry_t if PageSwapCache
+		 * Indicates order in the buddy system if PageBuddy
+		 */
+		unsigned long private;
+#if USE_SPLIT_PTE_PTLOCKS
+#if ALLOC_SPLIT_PTLOCKS
+		spinlock_t *ptl;
+#else
+		spinlock_t ptl;
+#endif
+#endif
+		void *s_mem;			/* slab first object */
+		unsigned long counters;		/* SLUB */
+		struct {			/* SLUB */
+			unsigned inuse:16;
+			unsigned objects:15;
+			unsigned frozen:1;
+		};
+	};
+
+	union {
+		/*
 		 * If the page is neither PageSlab nor mappable to userspace,
 		 * the value stored here may help determine what this page
 		 * is used for.  See page-flags.h for a list of page types
@@ -104,13 +122,7 @@ struct page {
 		 */
 		unsigned int page_type;
 
-		_slub_counter_t counters;
 		unsigned int active;		/* SLAB */
-		struct {			/* SLUB */
-			unsigned inuse:16;
-			unsigned objects:15;
-			unsigned frozen:1;
-		};
 		int units;			/* SLOB */
 
 		struct {			/* Page cache */
@@ -179,24 +191,6 @@ struct page {
 #endif
 	};
 
-	union {
-		/*
-		 * Mapping-private opaque data:
-		 * Usually used for buffer_heads if PagePrivate
-		 * Used for swp_entry_t if PageSwapCache
-		 * Indicates order in the buddy system if PageBuddy
-		 */
-		unsigned long private;
-#if USE_SPLIT_PTE_PTLOCKS
-#if ALLOC_SPLIT_PTLOCKS
-		spinlock_t *ptl;
-#else
-		spinlock_t ptl;
-#endif
-#endif
-		void *s_mem;			/* slab first object */
-	};
-
 #ifdef CONFIG_MEMCG
 	struct mem_cgroup *mem_cgroup;
 #endif