Commit cfc4ba53 authored by Jens Axboe's avatar Jens Axboe
Browse files

writeback: use RCU to protect bdi_list 



Now that bdi_writeback_all() no longer handles integrity writeback,
it doesn't have to block anymore. This means that we can switch
bdi_list reader side protection to RCU.

Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent f11fcae8

fs/fs-writeback.c

+3 −3
Original line number Diff line number Diff line
@@ -868,16 +868,16 @@ static void bdi_writeback_all(struct writeback_control *wbc) 


	WARN_ON(wbc->sync_mode == WB_SYNC_ALL);



	spin_lock(&bdi_lock);

	rcu_read_lock();



	list_for_each_entry(bdi, &bdi_list, bdi_list) {

	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {

		if (!bdi_has_dirty_io(bdi))

			continue;



		bdi_alloc_queue_work(bdi, wbc);

	}



	spin_unlock(&bdi_lock);

	rcu_read_unlock();

}



/*

include/linux/backing-dev.h

+1 −0
Original line number Diff line number Diff line
@@ -59,6 +59,7 @@ struct bdi_writeback { 


struct backing_dev_info {

	struct list_head bdi_list;

	struct rcu_head rcu_head;

	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */

	unsigned long state;	/* Always use atomic bitops on this */

	unsigned int capabilities; /* Device capabilities */

mm/backing-dev.c

+55 −21
Original line number Diff line number Diff line
@@ -26,6 +26,12 @@ struct backing_dev_info default_backing_dev_info = { 
EXPORT_SYMBOL_GPL(default_backing_dev_info);



static struct class *bdi_class;



/*

 * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as

 * reader side protection for bdi_pending_list. bdi_list has RCU reader side

 * locking.

 */

DEFINE_SPINLOCK(bdi_lock);

LIST_HEAD(bdi_list);

LIST_HEAD(bdi_pending_list);
@@ -284,9 +290,9 @@ static int bdi_start_fn(void *ptr) 
	/*

	 * Add us to the active bdi_list

	 */

	spin_lock(&bdi_lock);

	list_add(&bdi->bdi_list, &bdi_list);

	spin_unlock(&bdi_lock);

	spin_lock_bh(&bdi_lock);

	list_add_rcu(&bdi->bdi_list, &bdi_list);

	spin_unlock_bh(&bdi_lock);



	bdi_task_init(bdi, wb);
@@ -389,7 +395,7 @@ static int bdi_forker_task(void *ptr) 
		if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))

			wb_do_writeback(me, 0);



		spin_lock(&bdi_lock);

		spin_lock_bh(&bdi_lock);



		/*

		 * Check if any existing bdi's have dirty data without
@@ -410,7 +416,7 @@ static int bdi_forker_task(void *ptr) 
		if (list_empty(&bdi_pending_list)) {

			unsigned long wait;



			spin_unlock(&bdi_lock);

			spin_unlock_bh(&bdi_lock);

			wait = msecs_to_jiffies(dirty_writeback_interval * 10);

			schedule_timeout(wait);

			try_to_freeze();
@@ -426,7 +432,7 @@ static int bdi_forker_task(void *ptr) 
		bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,

				 bdi_list);

		list_del_init(&bdi->bdi_list);

		spin_unlock(&bdi_lock);

		spin_unlock_bh(&bdi_lock);



		wb = &bdi->wb;

		wb->task = kthread_run(bdi_start_fn, wb, "flush-%s",
@@ -445,9 +451,9 @@ static int bdi_forker_task(void *ptr) 
			 * a chance to flush other bdi's to free

			 * memory.

			 */

			spin_lock(&bdi_lock);

			spin_lock_bh(&bdi_lock);

			list_add_tail(&bdi->bdi_list, &bdi_pending_list);

			spin_unlock(&bdi_lock);

			spin_unlock_bh(&bdi_lock);



			bdi_flush_io(bdi);

		}
@@ -456,6 +462,24 @@ static int bdi_forker_task(void *ptr) 
	return 0;

}



static void bdi_add_to_pending(struct rcu_head *head)

{

	struct backing_dev_info *bdi;



	bdi = container_of(head, struct backing_dev_info, rcu_head);

	INIT_LIST_HEAD(&bdi->bdi_list);



	spin_lock(&bdi_lock);

	list_add_tail(&bdi->bdi_list, &bdi_pending_list);

	spin_unlock(&bdi_lock);



	/*

	 * We are now on the pending list, wake up bdi_forker_task()

	 * to finish the job and add us back to the active bdi_list

	 */

	wake_up_process(default_backing_dev_info.wb.task);

}



/*

 * Add the default flusher task that gets created for any bdi

 * that has dirty data pending writeout
@@ -478,16 +502,29 @@ void static bdi_add_default_flusher_task(struct backing_dev_info *bdi) 
	 * waiting for previous additions to finish.

	 */

	if (!test_and_set_bit(BDI_pending, &bdi->state)) {

		list_move_tail(&bdi->bdi_list, &bdi_pending_list);

		list_del_rcu(&bdi->bdi_list);



		/*

		 * We are now on the pending list, wake up bdi_forker_task()

		 * to finish the job and add us back to the active bdi_list

		 * We must wait for the current RCU period to end before

		 * moving to the pending list. So schedule that operation

		 * from an RCU callback.

		 */

		wake_up_process(default_backing_dev_info.wb.task);

		call_rcu(&bdi->rcu_head, bdi_add_to_pending);

	}

}



/*

 * Remove bdi from bdi_list, and ensure that it is no longer visible

 */

static void bdi_remove_from_list(struct backing_dev_info *bdi)

{

	spin_lock_bh(&bdi_lock);

	list_del_rcu(&bdi->bdi_list);

	spin_unlock_bh(&bdi_lock);



	synchronize_rcu();

}



int bdi_register(struct backing_dev_info *bdi, struct device *parent,

		const char *fmt, ...)

{
@@ -506,9 +543,9 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent, 
		goto exit;

	}



	spin_lock(&bdi_lock);

	list_add_tail(&bdi->bdi_list, &bdi_list);

	spin_unlock(&bdi_lock);

	spin_lock_bh(&bdi_lock);

	list_add_tail_rcu(&bdi->bdi_list, &bdi_list);

	spin_unlock_bh(&bdi_lock);



	bdi->dev = dev;
@@ -526,9 +563,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent, 
			wb->task = NULL;

			ret = -ENOMEM;



			spin_lock(&bdi_lock);

			list_del(&bdi->bdi_list);

			spin_unlock(&bdi_lock);

			bdi_remove_from_list(bdi);

			goto exit;

		}

	}
@@ -565,9 +600,7 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi) 
	/*

	 * Make sure nobody finds us on the bdi_list anymore

	 */

	spin_lock(&bdi_lock);

	list_del(&bdi->bdi_list);

	spin_unlock(&bdi_lock);

	bdi_remove_from_list(bdi);



	/*

	 * Finally, kill the kernel threads. We don't need to be RCU
@@ -599,6 +632,7 @@ int bdi_init(struct backing_dev_info *bdi) 
	bdi->max_ratio = 100;

	bdi->max_prop_frac = PROP_FRAC_BASE;

	spin_lock_init(&bdi->wb_lock);

	INIT_RCU_HEAD(&bdi->rcu_head);

	INIT_LIST_HEAD(&bdi->bdi_list);

	INIT_LIST_HEAD(&bdi->wb_list);

	INIT_LIST_HEAD(&bdi->work_list);

mm/page-writeback.c

+4 −4
Original line number Diff line number Diff line
@@ -315,7 +315,7 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 
{

	int ret = 0;



	spin_lock(&bdi_lock);

	spin_lock_bh(&bdi_lock);

	if (min_ratio > bdi->max_ratio) {

		ret = -EINVAL;

	} else {
@@ -327,7 +327,7 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio) 
			ret = -EINVAL;

		}

	}

	spin_unlock(&bdi_lock);

	spin_unlock_bh(&bdi_lock);



	return ret;

}
@@ -339,14 +339,14 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio) 
	if (max_ratio > 100)

		return -EINVAL;



	spin_lock(&bdi_lock);

	spin_lock_bh(&bdi_lock);

	if (bdi->min_ratio > max_ratio) {

		ret = -EINVAL;

	} else {

		bdi->max_ratio = max_ratio;

		bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;

	}

	spin_unlock(&bdi_lock);

	spin_unlock_bh(&bdi_lock);



	return ret;

}