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Commit 2a12f0dc authored by Tejun Heo's avatar Tejun Heo
Browse files

blk-throttle: make blk_throtl_drain() ready for hierarchy 



The current blk_throtl_drain() assumes that all active throtl_grps are
queued on throtl_data->service_queue, which won't be true once
hierarchy support is implemented.

This patch makes blk_throtl_drain() perform post-order walk of the
blkg hierarchy draining each associated throtl_grp, which guarantees
that all bios will eventually be pushed to the top-level service_queue
in throtl_data.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarVivek Goyal <vgoyal@redhat.com>
parent 6e1a5704

block/blk-throttle.c

+40 −11
Original line number Diff line number Diff line
@@ -1299,6 +1299,28 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) 
	return throttled;

}



/*

 * Dispatch all bios from all children tg's queued on @parent_sq.  On

 * return, @parent_sq is guaranteed to not have any active children tg's

 * and all bios from previously active tg's are on @parent_sq->bio_lists[].

 */

static void tg_drain_bios(struct throtl_service_queue *parent_sq)

{

	struct throtl_grp *tg;



	while ((tg = throtl_rb_first(parent_sq))) {

		struct throtl_service_queue *sq = &tg->service_queue;

		struct bio *bio;



		throtl_dequeue_tg(tg);



		while ((bio = bio_list_peek(&sq->bio_lists[READ])))

			tg_dispatch_one_bio(tg, bio_data_dir(bio));

		while ((bio = bio_list_peek(&sq->bio_lists[WRITE])))

			tg_dispatch_one_bio(tg, bio_data_dir(bio));

	}

}



/**

 * blk_throtl_drain - drain throttled bios

 * @q: request_queue to drain throttled bios for
@@ -1309,27 +1331,34 @@ void blk_throtl_drain(struct request_queue *q) 
	__releases(q->queue_lock) __acquires(q->queue_lock)

{

	struct throtl_data *td = q->td;

	struct throtl_service_queue *parent_sq = &td->service_queue;

	struct throtl_grp *tg;

	struct blkcg_gq *blkg;

	struct cgroup *pos_cgrp;

	struct bio *bio;

	int rw;



	queue_lockdep_assert_held(q);

	rcu_read_lock();



	while ((tg = throtl_rb_first(parent_sq))) {

		struct throtl_service_queue *sq = &tg->service_queue;

	/*

	 * Drain each tg while doing post-order walk on the blkg tree, so

	 * that all bios are propagated to td->service_queue.  It'd be

	 * better to walk service_queue tree directly but blkg walk is

	 * easier.

	 */

	blkg_for_each_descendant_post(blkg, pos_cgrp, td->queue->root_blkg)

		tg_drain_bios(&blkg_to_tg(blkg)->service_queue);



		throtl_dequeue_tg(tg);

	tg_drain_bios(&td_root_tg(td)->service_queue);



		while ((bio = bio_list_peek(&sq->bio_lists[READ])))

			tg_dispatch_one_bio(tg, bio_data_dir(bio));

		while ((bio = bio_list_peek(&sq->bio_lists[WRITE])))

			tg_dispatch_one_bio(tg, bio_data_dir(bio));

	}

	/* finally, transfer bios from top-level tg's into the td */

	tg_drain_bios(&td->service_queue);



	rcu_read_unlock();

	spin_unlock_irq(q->queue_lock);



	/* all bios now should be in td->service_queue, issue them */

	for (rw = READ; rw <= WRITE; rw++)

		while ((bio = bio_list_pop(&parent_sq->bio_lists[rw])))

		while ((bio = bio_list_pop(&td->service_queue.bio_lists[rw])))

			generic_make_request(bio);



	spin_lock_irq(q->queue_lock);