mm: enable hashdist by default on 64bit NUMA

On PowerPC we allocate large boot time hashes on node 0.  This leads to an
imbalance in the free memory, for example on a 64GB box (4 x 16GB nodes):

Free memory:
Node 0: 97.03%
Node 1: 98.54%
Node 2: 98.42%
Node 3: 98.53%

If we switch to using vmalloc (like ia64 and x86-64) things are more
balanced:

Free memory:
Node 0: 97.53%
Node 1: 98.35%
Node 2: 98.33%
Node 3: 98.33%

For many HPC applications we are limited by the free available memory on
the smallest node, so even though the same amount of memory is used the
better balancing helps.

Since all 64bit NUMA capable architectures should have sufficient vmalloc
space, it makes sense to enable it via CONFIG_64BIT.

Signed-off-by: Anton Blanchard <[email protected]>
Acked-by: David S. Miller <[email protected]>
Acked-by: Benjamin Herrenschmidt <[email protected]>
Acked-by: Ralf Baechle <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Richard Henderson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/bootmem.h

@@ -146,10 +146,10 @@ extern void *alloc_large_system_hash(const char *tablename,
 
 #define HASH_EARLY	0x00000001	/* Allocating during early boot? */
 
-/* Only NUMA needs hash distribution.
- * IA64 and x86_64 have sufficient vmalloc space.
+/* Only NUMA needs hash distribution. 64bit NUMA architectures have
+ * sufficient vmalloc space.
  */
-#if defined(CONFIG_NUMA) && (defined(CONFIG_IA64) || defined(CONFIG_X86_64))
+#if defined(CONFIG_NUMA) && defined(CONFIG_64BIT)
 #define HASHDIST_DEFAULT 1
 #else
 #define HASHDIST_DEFAULT 0