Commit 8fa72d23 authored by Jeff Moyer's avatar Jeff Moyer Committed by Jens Axboe
Browse files

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



In realtime environments, it may be desirable to keep the per-bdi
flusher threads from running on certain cpus.  This patch adds a
cpu_list file to /sys/class/bdi/* to enable this.  The default is to tie
the flusher threads to the same numa node as the backing device (though
I could be convinced to make it a mask of all cpus to avoid a change in
behaviour).

Thanks to Jeremy Eder for the original idea.

Signed-off-by: default avatarJeff Moyer <jmoyer@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent c304a51b

include/linux/backing-dev.h

+4 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#include <linux/writeback.h>

#include <linux/atomic.h>

#include <linux/sysctl.h>

#include <linux/mutex.h>



struct page;

struct device;
@@ -105,6 +106,9 @@ 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

+84 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#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);
@@ -221,12 +222,63 @@ 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,

};
@@ -428,6 +480,7 @@ 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()'.
@@ -437,6 +490,14 @@ 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);
@@ -509,6 +570,17 @@ 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));
@@ -634,6 +706,15 @@ 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)
@@ -656,6 +737,7 @@ int bdi_init(struct backing_dev_info *bdi) 
err:

		while (i--)

			percpu_counter_destroy(&bdi->bdi_stat[i]);

		kfree(bdi->flusher_cpumask);

	}



	return err;
@@ -683,6 +765,8 @@ 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()

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