mm,slub,x86: decouple size of struct page from CONFIG_CMPXCHG_LOCAL

While implementing cmpxchg_double() on s390 I realized that we don't set
CONFIG_CMPXCHG_LOCAL despite the fact that we have support for it.

However setting that option will increase the size of struct page by
eight bytes on 64 bit, which we certainly do not want.  Also, it doesn't
make sense that a present cpu feature should increase the size of struct
page.

Besides that it looks like the dependency to CMPXCHG_LOCAL is wrong and
that it should depend on CMPXCHG_DOUBLE instead.

This patch:

If an architecture supports CMPXCHG_LOCAL this shouldn't result
automatically in larger struct pages if the SLUB allocator is used.
Instead introduce a new config option "HAVE_ALIGNED_STRUCT_PAGE" which
can be selected if a double word aligned struct page is required.  Also
update x86 Kconfig so that it should work as before.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/Kconfig b/arch/Kconfig
index 2505740b81d2e24696ff4420f2f9af86713b817b..a2c5c077c32d1f5ada463af33e264ba536bdda1d 100644 (file)
--- 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 a150f4c35e945035001047136e704f01fb7f1e73..5201a2c272397436fdca0ac996ff0cd8409d3a33 100644 (file)
--- 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 5b42f1b34eb74b59964f9a717d436cad44481c05..3cc3062b37679d2bcb58d04c51c5b42073f61725 100644 (file)
--- 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 5d37b5e44140f2cd0884fc1ae7798ec02b0afb12..72aa8413460932bf0826cf3d40bf52798a0e9ab9 100644 (file)
--- 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;