sched: convert nohz_cpu_mask to cpumask_var_t.

Impact: (future) size reduction for large NR_CPUS.

Dynamically allocating cpumasks (when CONFIG_CPUMASK_OFFSTACK) saves
space for small nr_cpu_ids but big CONFIG_NR_CPUS.  cpumask_var_t
is just a struct cpumask for !CONFIG_CPUMASK_OFFSTACK.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 11 insertions, 8 deletions

diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index e503a002f330..c03ca3e61919 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -393,7 +393,7 @@ static void rcu_start_batch(struct rcu_ctrlblk *rcp)
                  * unnecessarily.
                  */
                 smp_mb();
-                cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
+                cpumask_andnot(&rcp->cpumask, cpu_online_mask, nohz_cpu_mask);
 
                 rcp->signaled = 0;
         }
diff --git a/kernel/sched.c b/kernel/sched.c
index 6b9606a6cabf..2723d7a4a42d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5870,9 +5870,9 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
  * indicates which cpus entered this state. This is used
  * in the rcu update to wait only for active cpus. For system
  * which do not switch off the HZ timer nohz_cpu_mask should
- * always be CPU_MASK_NONE.
+ * always be CPU_BITS_NONE.
  */
-cpumask_t nohz_cpu_mask = CPU_MASK_NONE;
+cpumask_var_t nohz_cpu_mask;
 
 /*
  * Increase the granularity value when there are more CPUs,
@@ -8274,6 +8274,9 @@ void __init sched_init(void)
          */
         current->sched_class = &fair_sched_class;
 
+        /* Allocate the nohz_cpu_mask if CONFIG_CPUMASK_OFFSTACK */
+        alloc_bootmem_cpumask_var(&nohz_cpu_mask);
+
         scheduler_running = 1;
 }
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 342fc9ccab46..70f872c71f4e 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -144,7 +144,7 @@ void tick_nohz_update_jiffies(void)
         if (!ts->tick_stopped)
                 return;
 
-        cpu_clear(cpu, nohz_cpu_mask);
+        cpumask_clear_cpu(cpu, nohz_cpu_mask);
         now = ktime_get();
         ts->idle_waketime = now;
 
@@ -283,7 +283,7 @@ void tick_nohz_stop_sched_tick(int inidle)
         if ((long)delta_jiffies >= 1) {
 
                 if (delta_jiffies > 1)
-                        cpu_set(cpu, nohz_cpu_mask);
+                        cpumask_set_cpu(cpu, nohz_cpu_mask);
                 /*
                  * nohz_stop_sched_tick can be called several times before
                  * the nohz_restart_sched_tick is called. This happens when
@@ -296,7 +296,7 @@ void tick_nohz_stop_sched_tick(int inidle)
                                 /*
                                  * sched tick not stopped!
                                  */
-                                cpu_clear(cpu, nohz_cpu_mask);
+                                cpumask_clear_cpu(cpu, nohz_cpu_mask);
                                 goto out;
                         }
 
@@ -354,7 +354,7 @@ void tick_nohz_stop_sched_tick(int inidle)
                  * softirq.
                  */
                 tick_do_update_jiffies64(ktime_get());
-                cpu_clear(cpu, nohz_cpu_mask);
+                cpumask_clear_cpu(cpu, nohz_cpu_mask);
         }
         raise_softirq_irqoff(TIMER_SOFTIRQ);
 out:
@@ -432,7 +432,7 @@ void tick_nohz_restart_sched_tick(void)
         select_nohz_load_balancer(0);
         now = ktime_get();
         tick_do_update_jiffies64(now);
-        cpu_clear(cpu, nohz_cpu_mask);
+        cpumask_clear_cpu(cpu, nohz_cpu_mask);
 
         /*
          * We stopped the tick in idle. Update process times would miss the