[PATCH] Use alloc_percpu to allocate workqueues locally

This patch makes the workqueus use alloc_percpu instead of an array.  The
workqueues are placed on nodes local to each processor.

The workqueue structure can grow to a significant size on a system with
lots of processors if this patch is not applied.  64 bit architectures with
all debugging features enabled and configured for 512 processors will not
be able to boot without this patch.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/workqueue.c

@@ -12,6 +12,8 @@
  *   Andrew Morton <andrewm@uow.edu.au>
  *   Kai Petzke <wpp@marie.physik.tu-berlin.de>
  *   Theodore Ts'o <tytso@mit.edu>
+ *
+ * Made to use alloc_percpu by Christoph Lameter <clameter@sgi.com>.
  */
 
 #include <linux/module.h>
@@ -57,7 +59,7 @@ struct cpu_workqueue_struct {
  * per-CPU workqueues:
  */
 struct workqueue_struct {
-	struct cpu_workqueue_struct cpu_wq[NR_CPUS];
+	struct cpu_workqueue_struct *cpu_wq;
 	const char *name;
 	struct list_head list; 	/* Empty if single thread */
 };
@@ -102,7 +104,7 @@ int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
 		if (unlikely(is_single_threaded(wq)))
 			cpu = 0;
 		BUG_ON(!list_empty(&work->entry));
-		__queue_work(wq->cpu_wq + cpu, work);
+		__queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 		ret = 1;
 	}
 	put_cpu();
@@ -118,7 +120,7 @@ static void delayed_work_timer_fn(unsigned long __data)
 	if (unlikely(is_single_threaded(wq)))
 		cpu = 0;
 
-	__queue_work(wq->cpu_wq + cpu, work);
+	__queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 }
 
 int fastcall queue_delayed_work(struct workqueue_struct *wq,
@@ -265,13 +267,13 @@ void fastcall flush_workqueue(struct workqueue_struct *wq)
 
 	if (is_single_threaded(wq)) {
 		/* Always use cpu 0's area. */
-		flush_cpu_workqueue(wq->cpu_wq + 0);
+		flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, 0));
 	} else {
 		int cpu;
 
 		lock_cpu_hotplug();
 		for_each_online_cpu(cpu)
-			flush_cpu_workqueue(wq->cpu_wq + cpu);
+			flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
 		unlock_cpu_hotplug();
 	}
 }
@@ -279,7 +281,7 @@ void fastcall flush_workqueue(struct workqueue_struct *wq)
 static struct task_struct *create_workqueue_thread(struct workqueue_struct *wq,
 						   int cpu)
 {
-	struct cpu_workqueue_struct *cwq = wq->cpu_wq + cpu;
+	struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 	struct task_struct *p;
 
 	spin_lock_init(&cwq->lock);
@@ -312,6 +314,7 @@ struct workqueue_struct *__create_workqueue(const char *name,
 	if (!wq)
 		return NULL;
 
+	wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
 	wq->name = name;
 	/* We don't need the distraction of CPUs appearing and vanishing. */
 	lock_cpu_hotplug();
@@ -353,7 +356,7 @@ static void cleanup_workqueue_thread(struct workqueue_struct *wq, int cpu)
 	unsigned long flags;
 	struct task_struct *p;
 
-	cwq = wq->cpu_wq + cpu;
+	cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 	spin_lock_irqsave(&cwq->lock, flags);
 	p = cwq->thread;
 	cwq->thread = NULL;
@@ -380,6 +383,7 @@ void destroy_workqueue(struct workqueue_struct *wq)
 		spin_unlock(&workqueue_lock);
 	}
 	unlock_cpu_hotplug();
+	free_percpu(wq->cpu_wq);
 	kfree(wq);
 }
 
@@ -458,7 +462,7 @@ int current_is_keventd(void)
 
 	BUG_ON(!keventd_wq);
 
-	cwq = keventd_wq->cpu_wq + cpu;
+	cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
 	if (current == cwq->thread)
 		ret = 1;
 
@@ -470,7 +474,7 @@ int current_is_keventd(void)
 /* Take the work from this (downed) CPU. */
 static void take_over_work(struct workqueue_struct *wq, unsigned int cpu)
 {
-	struct cpu_workqueue_struct *cwq = wq->cpu_wq + cpu;
+	struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 	LIST_HEAD(list);
 	struct work_struct *work;
 
@@ -481,7 +485,7 @@ static void take_over_work(struct workqueue_struct *wq, unsigned int cpu)
 		printk("Taking work for %s\n", wq->name);
 		work = list_entry(list.next,struct work_struct,entry);
 		list_del(&work->entry);
-		__queue_work(wq->cpu_wq + smp_processor_id(), work);
+		__queue_work(per_cpu_ptr(wq->cpu_wq, smp_processor_id()), work);
 	}
 	spin_unlock_irq(&cwq->lock);
 }
@@ -508,15 +512,18 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 	case CPU_ONLINE:
 		/* Kick off worker threads. */
 		list_for_each_entry(wq, &workqueues, list) {
-			kthread_bind(wq->cpu_wq[hotcpu].thread, hotcpu);
-			wake_up_process(wq->cpu_wq[hotcpu].thread);
+			struct cpu_workqueue_struct *cwq;
+
+			cwq = per_cpu_ptr(wq->cpu_wq, hotcpu);
+			kthread_bind(cwq->thread, hotcpu);
+			wake_up_process(cwq->thread);
 		}
 		break;
 
 	case CPU_UP_CANCELED:
 		list_for_each_entry(wq, &workqueues, list) {
 			/* Unbind so it can run. */
-			kthread_bind(wq->cpu_wq[hotcpu].thread,
+			kthread_bind(per_cpu_ptr(wq->cpu_wq, hotcpu)->thread,
 				     smp_processor_id());
 			cleanup_workqueue_thread(wq, hotcpu);
 		}