page allocator: use a pre-calculated value instead of num_online_nodes() in fast paths
num_online_nodes() is called in a number of places but most often by the
page allocator when deciding whether the zonelist needs to be filtered
based on cpusets or the zonelist cache. This is actually a heavy function
and touches a number of cache lines.
This patch stores the number of online nodes at boot time and updates the
value when nodes get onlined and offlined. The value is then used in a
number of important paths in place of num_online_nodes().
[rientjes@google.com: do not override definition of node_set_online() with macro]
Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
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: David Rientjes <rientjes@google.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 e60e414..0c9f406 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -161,7 +161,9 @@
#if MAX_NUMNODES > 1
int nr_node_ids __read_mostly = MAX_NUMNODES;
+int nr_online_nodes __read_mostly = 1;
EXPORT_SYMBOL(nr_node_ids);
+EXPORT_SYMBOL(nr_online_nodes);
#endif
int page_group_by_mobility_disabled __read_mostly;
@@ -1466,7 +1468,7 @@
if (NUMA_BUILD)
zlc_mark_zone_full(zonelist, z);
try_next_zone:
- if (NUMA_BUILD && !did_zlc_setup && num_online_nodes() > 1) {
+ if (NUMA_BUILD && !did_zlc_setup && nr_online_nodes > 1) {
/*
* we do zlc_setup after the first zone is tried but only
* if there are multiple nodes make it worthwhile
@@ -2265,7 +2267,7 @@
}
-#define MAX_NODE_LOAD (num_online_nodes())
+#define MAX_NODE_LOAD (nr_online_nodes)
static int node_load[MAX_NUMNODES];
/**
@@ -2474,7 +2476,7 @@
/* NUMA-aware ordering of nodes */
local_node = pgdat->node_id;
- load = num_online_nodes();
+ load = nr_online_nodes;
prev_node = local_node;
nodes_clear(used_mask);
@@ -2625,7 +2627,7 @@
printk("Built %i zonelists in %s order, mobility grouping %s. "
"Total pages: %ld\n",
- num_online_nodes(),
+ nr_online_nodes,
zonelist_order_name[current_zonelist_order],
page_group_by_mobility_disabled ? "off" : "on",
vm_total_pages);