4 files changed, 16 insertions, 8 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 2505740b81d2..a2c5c077c32d 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -185,4 +185,12 @@ config HAVE_RCU_TABLE_FREE
 config ARCH_HAVE_NMI_SAFE_CMPXCHG
         bool
 
+config HAVE_ALIGNED_STRUCT_PAGE
+        bool
+        help
+          This makes sure that struct pages are double word aligned and that
+          e.g. the SLUB allocator can perform double word atomic operations
+          on a struct page for better performance. However selecting this
+          might increase the size of a struct page by a word.
+
 source "kernel/gcov/Kconfig"
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a150f4c35e94..5201a2c27239 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -60,6 +60,7 @@ config X86
         select PERF_EVENTS
         select HAVE_PERF_EVENTS_NMI
         select ANON_INODES
+        select HAVE_ALIGNED_STRUCT_PAGE if SLUB && !M386
         select HAVE_ARCH_KMEMCHECK
         select HAVE_USER_RETURN_NOTIFIER
         select ARCH_BINFMT_ELF_RANDOMIZE_PIE
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5b42f1b34eb7..3cc3062b3767 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -151,12 +151,11 @@ struct page {
 #endif
 }
 /*
- * If another subsystem starts using the double word pairing for atomic
- * operations on struct page then it must change the #if to ensure
- * proper alignment of the page struct.
+ * The struct page can be forced to be double word aligned so that atomic ops
+ * on double words work. The SLUB allocator can make use of such a feature.
  */
-#if defined(CONFIG_SLUB) && defined(CONFIG_CMPXCHG_LOCAL)
-        __attribute__((__aligned__(2*sizeof(unsigned long))))
+#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
+        __aligned(2 * sizeof(unsigned long))
 #endif
 ;
 
diff --git a/mm/slub.c b/mm/slub.c
index 5d37b5e44140..72aa84134609 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -366,7 +366,7 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page
                 const char *n)
 {
         VM_BUG_ON(!irqs_disabled());
-#ifdef CONFIG_CMPXCHG_DOUBLE
+#if defined(CONFIG_CMPXCHG_DOUBLE) && defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
         if (s->flags & __CMPXCHG_DOUBLE) {
                 if (cmpxchg_double(&page->freelist, &page->counters,
                         freelist_old, counters_old,
@@ -400,7 +400,7 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
                 void *freelist_new, unsigned long counters_new,
                 const char *n)
 {
-#ifdef CONFIG_CMPXCHG_DOUBLE
+#if defined(CONFIG_CMPXCHG_DOUBLE) && defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
         if (s->flags & __CMPXCHG_DOUBLE) {
                 if (cmpxchg_double(&page->freelist, &page->counters,
                         freelist_old, counters_old,
@@ -3014,7 +3014,7 @@ static int kmem_cache_open(struct kmem_cache *s,
                 }
         }
 
-#ifdef CONFIG_CMPXCHG_DOUBLE
+#if defined(CONFIG_CMPXCHG_DOUBLE) && defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
         if (system_has_cmpxchg_double() && (s->flags & SLAB_DEBUG_FLAGS) == 0)
                 /* Enable fast mode */
                 s->flags |= __CMPXCHG_DOUBLE;