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>

2 files changed, 9 insertions, 0 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