page allocator: do not setup zonelist cache when there is only one node

There is a zonelist cache which is used to track zones that are not in the
allowed cpuset or found to be recently full.  This is to reduce cache
footprint on large machines.  On smaller machines, it just incurs cost for
no gain.  This patch only uses the zonelist cache when there are NUMA
nodes.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 03a386d24ef237c03305c4517df511360ad5fbd5..fd8e3ca0cf3b9aeee96bb70dd9f5c33bffbbc335 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1464,8 +1464,11 @@ this_zone_full:
                if (NUMA_BUILD)
                        zlc_mark_zone_full(zonelist, z);
 try_next_zone:
-               if (NUMA_BUILD && !did_zlc_setup) {
-                       /* we do zlc_setup after the first zone is tried */
+               if (NUMA_BUILD && !did_zlc_setup && num_online_nodes() > 1) {
+                       /*
+                        * we do zlc_setup after the first zone is tried but only
+                        * if there are multiple nodes make it worthwhile
+                        */
                        allowednodes = zlc_setup(zonelist, alloc_flags);
                        zlc_active = 1;
                        did_zlc_setup = 1;