sched/numa: Turn some magic numbers into #defines

Cleanup suggested by Mel Gorman. Now the code contains some more
hints on what statistics go where.

Suggested-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Chegu Vinod <chegu_vinod@hp.com>
Link: http://lkml.kernel.org/r/1390860228-21539-10-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -896,6 +896,15 @@ struct numa_group {
 	unsigned long faults[0];
 };
 
+/* Shared or private faults. */
+#define NR_NUMA_HINT_FAULT_TYPES 2
+
+/* Memory and CPU locality */
+#define NR_NUMA_HINT_FAULT_STATS (NR_NUMA_HINT_FAULT_TYPES * 2)
+
+/* Averaged statistics, and temporary buffers. */
+#define NR_NUMA_HINT_FAULT_BUCKETS (NR_NUMA_HINT_FAULT_STATS * 2)
+
 pid_t task_numa_group_id(struct task_struct *p)
 {
 	return p->numa_group ? p->numa_group->gid : 0;
@@ -903,7 +912,7 @@ pid_t task_numa_group_id(struct task_struct *p)
 
 static inline int task_faults_idx(int nid, int priv)
 {
-	return 2 * nid + priv;
+	return NR_NUMA_HINT_FAULT_TYPES * nid + priv;
 }
 
 static inline unsigned long task_faults(struct task_struct *p, int nid)
@@ -1509,7 +1518,7 @@ static void task_numa_placement(struct task_struct *p)
 		unsigned long faults = 0, group_faults = 0;
 		int priv, i;
 
-		for (priv = 0; priv < 2; priv++) {
+		for (priv = 0; priv < NR_NUMA_HINT_FAULT_TYPES; priv++) {
 			long diff, f_diff, f_weight;
 
 			i = task_faults_idx(nid, priv);
@@ -1620,11 +1629,12 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
 		INIT_LIST_HEAD(&grp->task_list);
 		grp->gid = p->pid;
 		/* Second half of the array tracks nids where faults happen */
-		grp->faults_cpu = grp->faults + 2 * nr_node_ids;
+		grp->faults_cpu = grp->faults + NR_NUMA_HINT_FAULT_TYPES *
+						nr_node_ids;
 
 		node_set(task_node(current), grp->active_nodes);
 
-		for (i = 0; i < 4*nr_node_ids; i++)
+		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
 			grp->faults[i] = p->numa_faults_memory[i];
 
 		grp->total_faults = p->total_numa_faults;
@@ -1682,7 +1692,7 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
 
 	double_lock(&my_grp->lock, &grp->lock);
 
-	for (i = 0; i < 4*nr_node_ids; i++) {
+	for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
 		my_grp->faults[i] -= p->numa_faults_memory[i];
 		grp->faults[i] += p->numa_faults_memory[i];
 	}
@@ -1714,7 +1724,7 @@ void task_numa_free(struct task_struct *p)
 
 	if (grp) {
 		spin_lock(&grp->lock);
-		for (i = 0; i < 4*nr_node_ids; i++)
+		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
 			grp->faults[i] -= p->numa_faults_memory[i];
 		grp->total_faults -= p->total_numa_faults;
 
@@ -1755,14 +1765,20 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
 
 	/* Allocate buffer to track faults on a per-node basis */
 	if (unlikely(!p->numa_faults_memory)) {
-		int size = sizeof(*p->numa_faults_memory) * 4 * nr_node_ids;
+		int size = sizeof(*p->numa_faults_memory) *
+			   NR_NUMA_HINT_FAULT_BUCKETS * nr_node_ids;
 
-		/* numa_faults and numa_faults_buffer share the allocation */
-		p->numa_faults_memory = kzalloc(size * 2, GFP_KERNEL|__GFP_NOWARN);
+		p->numa_faults_memory = kzalloc(size, GFP_KERNEL|__GFP_NOWARN);
 		if (!p->numa_faults_memory)
 			return;
 
 		BUG_ON(p->numa_faults_buffer_memory);
+		/*
+		 * The averaged statistics, shared & private, memory & cpu,
+		 * occupy the first half of the array. The second half of the
+		 * array is for current counters, which are averaged into the
+		 * first set by task_numa_placement.
+		 */
 		p->numa_faults_cpu = p->numa_faults_memory + (2 * nr_node_ids);
 		p->numa_faults_buffer_memory = p->numa_faults_memory + (4 * nr_node_ids);
 		p->numa_faults_buffer_cpu = p->numa_faults_memory + (6 * nr_node_ids);