---

yaml
---
r: 284351
b: refs/heads/master
c: 43570fd
h: refs/heads/master
i:
  284349: 9527de1
  284347: 2c84270
  284343: 5627439
  284335: a0411dd
  284319: 7d7bcc5
  284287: 9585608
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 0d259cf8190b9c446eefd5225ffcc3941e76a432
+refs/heads/master: 43570fd2f47ba518145e9289f54cde3dba4c8b25

trunk/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"

trunk/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

trunk/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
 ;
 

trunk/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;