[PATCH 19/27] Do not setup zonelist cache when there is only one node

[Mel Gorman]

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@xxxxxxxxx>
Reviewed-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
---
 mm/page_alloc.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c4eb295..01cd489 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1442,6 +1442,8 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
 	/* Determine in advance if the zonelist needs filtering */
 	if ((alloc_flags & ALLOC_CPUSET) && unlikely(number_of_cpusets > 1))
 		zonelist_filter = 1;
+	if (num_online_nodes() > 1)
+		zonelist_filter = 1;
 
 zonelist_scan:
 	/*
@@ -1486,8 +1488,12 @@ this_zone_full:
 			zlc_mark_zone_full(zonelist, z);
 try_next_zone:
 		if (NUMA_BUILD && zonelist_filter) {
-			if (!did_zlc_setup) {
-				/* do zlc_setup after the first zone is tried */
+			if (!did_zlc_setup && num_online_nodes() > 1) {
+				/*
+				 * do zlc_setup after the first zone is tried
+				 * but only if there are multiple nodes to make
+				 * it worthwhile
+				 */
 				allowednodes = zlc_setup(zonelist, alloc_flags);
 				zlc_active = 1;
 			}
-- 
1.5.6.5

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