SLUB: Allow full duplication of kmalloc array for 390

Commit 756dee7587 ("SLUB: Get rid of dynamic DMA
kmalloc cache allocation") makes S390 run out of kmalloc caches.  Increase the
number of kmalloc caches to a safe size.

Cc: <stable@kernel.org> [ .33 and .34 ]
Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Tested-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

include/linux/slub_def.h

@@ -137,7 +137,7 @@ struct kmem_cache {
 #ifdef CONFIG_ZONE_DMA
 #define SLUB_DMA __GFP_DMA
 /* Reserve extra caches for potential DMA use */
-#define KMALLOC_CACHES (2 * SLUB_PAGE_SHIFT - 6)
+#define KMALLOC_CACHES (2 * SLUB_PAGE_SHIFT)
 #else
 /* Disable DMA functionality */
 #define SLUB_DMA (__force gfp_t)0