Revert "bdi: add a user-tunable cpu_list for the bdi flusher threads"

This reverts commit 8fa72d23.

People disagree about how this should be done, so let's revert this for
now so that nobody starts using the new tuning interface.  Tejun is
thinking about a more generic interface for thread pool affinity.
Requested-by: NTejun Heo <tj@kernel.org>
Acked-by: NJeff Moyer <jmoyer@redhat.com>
Acked-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/backing-dev.h

@@ -18,7 +18,6 @@
 #include <linux/writeback.h>
 #include <linux/atomic.h>
 #include <linux/sysctl.h>
-#include <linux/mutex.h>
 
 struct page;
 struct device;
@@ -106,9 +105,6 @@ struct backing_dev_info {
 
 	struct timer_list laptop_mode_wb_timer;
 
-	cpumask_t *flusher_cpumask; /* used for writeback thread scheduling */
-	struct mutex flusher_cpumask_lock;
-
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *debug_dir;
 	struct dentry *debug_stats;

mm/backing-dev.c

@@ -10,7 +10,6 @@
 #include <linux/module.h>
 #include <linux/writeback.h>
 #include <linux/device.h>
-#include <linux/slab.h>
 #include <trace/events/writeback.h>
 
 static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
@@ -222,63 +221,12 @@ static ssize_t max_ratio_store(struct device *dev,
 }
 BDI_SHOW(max_ratio, bdi->max_ratio)
 
-static ssize_t cpu_list_store(struct device *dev,
-		struct device_attribute *attr, const char *buf, size_t count)
-{
-	struct backing_dev_info *bdi = dev_get_drvdata(dev);
-	struct bdi_writeback *wb = &bdi->wb;
-	cpumask_var_t newmask;
-	ssize_t ret;
-	struct task_struct *task;
-
-	if (!alloc_cpumask_var(&newmask, GFP_KERNEL))
-		return -ENOMEM;
-
-	ret = cpulist_parse(buf, newmask);
-	if (!ret) {
-		spin_lock_bh(&bdi->wb_lock);
-		task = wb->task;
-		if (task)
-			get_task_struct(task);
-		spin_unlock_bh(&bdi->wb_lock);
-
-		mutex_lock(&bdi->flusher_cpumask_lock);
-		if (task) {
-			ret = set_cpus_allowed_ptr(task, newmask);
-			put_task_struct(task);
-		}
-		if (ret == 0) {
-			cpumask_copy(bdi->flusher_cpumask, newmask);
-			ret = count;
-		}
-		mutex_unlock(&bdi->flusher_cpumask_lock);
-
-	}
-	free_cpumask_var(newmask);
-
-	return ret;
-}
-
-static ssize_t cpu_list_show(struct device *dev,
-		struct device_attribute *attr, char *page)
-{
-	struct backing_dev_info *bdi = dev_get_drvdata(dev);
-	ssize_t ret;
-
-	mutex_lock(&bdi->flusher_cpumask_lock);
-	ret = cpulist_scnprintf(page, PAGE_SIZE-1, bdi->flusher_cpumask);
-	mutex_unlock(&bdi->flusher_cpumask_lock);
-
-	return ret;
-}
-
 #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
 
 static struct device_attribute bdi_dev_attrs[] = {
 	__ATTR_RW(read_ahead_kb),
 	__ATTR_RW(min_ratio),
 	__ATTR_RW(max_ratio),
-	__ATTR_RW(cpu_list),
 	__ATTR_NULL,
 };
 
@@ -480,7 +428,6 @@ static int bdi_forker_thread(void *ptr)
 				writeback_inodes_wb(&bdi->wb, 1024,
 						    WB_REASON_FORKER_THREAD);
 			} else {
-				int ret;
 				/*
 				 * The spinlock makes sure we do not lose
 				 * wake-ups when racing with 'bdi_queue_work()'.
@@ -490,14 +437,6 @@ static int bdi_forker_thread(void *ptr)
 				spin_lock_bh(&bdi->wb_lock);
 				bdi->wb.task = task;
 				spin_unlock_bh(&bdi->wb_lock);
-				mutex_lock(&bdi->flusher_cpumask_lock);
-				ret = set_cpus_allowed_ptr(task,
-							bdi->flusher_cpumask);
-				mutex_unlock(&bdi->flusher_cpumask_lock);
-				if (ret)
-					printk_once("%s: failed to bind flusher"
-						    " thread %s, error %d\n",
-						    __func__, task->comm, ret);
 				wake_up_process(task);
 			}
 			bdi_clear_pending(bdi);
@@ -570,17 +509,6 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 						dev_name(dev));
 		if (IS_ERR(wb->task))
 			return PTR_ERR(wb->task);
-	} else {
-		int node;
-		/*
-		 * Set up a default cpumask for the flusher threads that
-		 * includes all cpus on the same numa node as the device.
-		 * The mask may be overridden via sysfs.
-		 */
-		node = dev_to_node(bdi->dev);
-		if (node != NUMA_NO_NODE)
-			cpumask_copy(bdi->flusher_cpumask,
-				     cpumask_of_node(node));
 	}
 
 	bdi_debug_register(bdi, dev_name(dev));
@@ -706,15 +634,6 @@ int bdi_init(struct backing_dev_info *bdi)
 
 	bdi_wb_init(&bdi->wb, bdi);
 
-	if (!bdi_cap_flush_forker(bdi)) {
-		bdi->flusher_cpumask = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
-		if (!bdi->flusher_cpumask)
-			return -ENOMEM;
-		cpumask_setall(bdi->flusher_cpumask);
-		mutex_init(&bdi->flusher_cpumask_lock);
-	} else
-		bdi->flusher_cpumask = NULL;
-
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 		err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 		if (err)
@@ -737,7 +656,6 @@ int bdi_init(struct backing_dev_info *bdi)
 err:
 		while (i--)
 			percpu_counter_destroy(&bdi->bdi_stat[i]);
-		kfree(bdi->flusher_cpumask);
 	}
 
 	return err;
@@ -765,8 +683,6 @@ void bdi_destroy(struct backing_dev_info *bdi)
 
 	bdi_unregister(bdi);
 
-	kfree(bdi->flusher_cpumask);
-
 	/*
 	 * If bdi_unregister() had already been called earlier, the
 	 * wakeup_timer could still be armed because bdi_prune_sb()