Re: [PATCH 20/35] Use a pre-calculated value for num_online_nodes()

[Mel Gorman <mel@csn.ul.ie>]

On Thu, Mar 19, 2009 at 04:43:55PM -0400, Christoph Lameter wrote:
> Trying to the same in the style of nr_node_ids etc.
> 

Because of some issues with the patch and what it does for possible
nodes, I reworked the patch slightly into the following and is what I'm
actually testing.

commit 58652d22798591d4df5421a90d65cbd7e60b9048
Author: Christoph Lameter <cl@linux-foundation.org>
Date:   Thu Mar 19 21:34:17 2009 +0000

    Use a pre-calculated value for num_online_nodes()
    
    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.
    
    Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
    Signed-off-by: Mel Gorman <mel@csn.ul.ie>

diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index 848025c..474e73e 100644
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -408,6 +408,19 @@ static inline int num_node_state(enum node_states state)
 #define next_online_node(nid)	next_node((nid), node_states[N_ONLINE])
 
 extern int nr_node_ids;
+extern int nr_online_nodes;
+
+static inline void node_set_online(int nid)
+{
+	node_set_state(nid, N_ONLINE);
+	nr_online_nodes = num_node_state(N_ONLINE);
+}
+
+static inline void node_set_offline(int nid)
+{
+	node_clear_state(nid, N_ONLINE);
+	nr_online_nodes = num_node_state(N_ONLINE);
+}
 #else
 
 static inline int node_state(int node, enum node_states state)
@@ -434,7 +447,7 @@ static inline int num_node_state(enum node_states state)
 #define first_online_node	0
 #define next_online_node(nid)	(MAX_NUMNODES)
 #define nr_node_ids		1
-
+#define nr_online_nodes		1
 #endif
 
 #define node_online_map 	node_states[N_ONLINE]
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1e99997..210e28c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -875,7 +875,7 @@ static void return_unused_surplus_pages(struct hstate *h,
 	 * can no longer free unreserved surplus pages. This occurs when
 	 * the nodes with surplus pages have no free pages.
 	 */
-	unsigned long remaining_iterations = num_online_nodes();
+	unsigned long remaining_iterations = nr_online_nodes;
 
 	/* Uncommit the reservation */
 	h->resv_huge_pages -= unused_resv_pages;
@@ -904,7 +904,7 @@ static void return_unused_surplus_pages(struct hstate *h,
 			h->surplus_huge_pages--;
 			h->surplus_huge_pages_node[nid]--;
 			nr_pages--;
-			remaining_iterations = num_online_nodes();
+			remaining_iterations = nr_online_nodes;
 		}
 	}
 }
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 18f0b56..4131ff9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -164,7 +164,9 @@ static unsigned long __meminitdata dma_reserve;
 
 #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;
@@ -1445,7 +1447,7 @@ 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)
+	if (nr_online_nodes > 1)
 		zonelist_filter = 1;
 
 zonelist_scan:
@@ -1486,7 +1488,7 @@ this_zone_full:
 			zlc_mark_zone_full(zonelist, z);
 try_next_zone:
 		if (NUMA_BUILD && zonelist_filter) {
-			if (!did_zlc_setup && num_online_nodes() > 1) {
+			if (!did_zlc_setup && nr_online_nodes > 1) {
 				/*
 				 * do zlc_setup after the first zone is tried
 				 * but only if there are multiple nodes to make
@@ -2285,7 +2287,7 @@ int numa_zonelist_order_handler(ctl_table *table, int write,
 }
 
 
-#define MAX_NODE_LOAD (num_online_nodes())
+#define MAX_NODE_LOAD (nr_online_nodes)
 static int node_load[MAX_NUMNODES];
 
 /**
@@ -2494,7 +2496,7 @@ static void build_zonelists(pg_data_t *pgdat)
 
 	/* 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);
 
@@ -2645,7 +2647,7 @@ void build_all_zonelists(void)
 
 	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);
diff --git a/mm/slab.c b/mm/slab.c
index e7f1ded..e6157a0 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3526,7 +3526,7 @@ static inline void __cache_free(struct kmem_cache *cachep, void *objp)
 	 * variable to skip the call, which is mostly likely to be present in
 	 * the cache.
 	 */
-	if (numa_platform && cache_free_alien(cachep, objp))
+	if (numa_platform > 1 && cache_free_alien(cachep, objp))
 		return;
 
 	if (likely(ac->avail < ac->limit)) {
diff --git a/mm/slub.c b/mm/slub.c
index 0280eee..8ce6be8 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3648,7 +3648,7 @@ static int list_locations(struct kmem_cache *s, char *buf,
 						 to_cpumask(l->cpus));
 		}
 
-		if (num_online_nodes() > 1 && !nodes_empty(l->nodes) &&
+		if (nr_online_nodes > 1 && !nodes_empty(l->nodes) &&
 				len < PAGE_SIZE - 60) {
 			len += sprintf(buf + len, " nodes=");
 			len += nodelist_scnprintf(buf + len, PAGE_SIZE - len - 50,
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index c51fed4..ba9eb8f 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -124,7 +124,7 @@ svc_pool_map_choose_mode(void)
 {
 	unsigned int node;
 
-	if (num_online_nodes() > 1) {
+	if (nr_online_nodes > 1) {
 		/*
 		 * Actually have multiple NUMA nodes,
 		 * so split pools on NUMA node boundaries

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