blkio: Core implementation of throttle policy

o Actual implementation of throttling policy in block layer. Currently it
  implements READ and WRITE bytes per second throttling logic. IOPS throttling
  comes in later patches.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

4 files changed, 946 insertions, 0 deletions

diff --git a/block/Kconfig b/block/Kconfig
index 9be0b56eaee1..6c9213ef15a1 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -77,6 +77,18 @@ config BLK_DEV_INTEGRITY
 	T10/SCSI Data Integrity Field or the T13/ATA External Path
 	Protection.  If in doubt, say N.
 
+config BLK_DEV_THROTTLING
+	bool "Block layer bio throttling support"
+	depends on BLK_CGROUP=y && EXPERIMENTAL
+	default n
+	---help---
+	Block layer bio throttling support. It can be used to limit
+	the IO rate to a device. IO rate policies are per cgroup and
+	one needs to mount and use blkio cgroup controller for creating
+	cgroups and specifying per device IO rate policies.
+
+	See Documentation/cgroups/blkio-controller.txt for more information.
+
 endif # BLOCK
 
 config BLOCK_COMPAT
diff --git a/block/Makefile b/block/Makefile
index 0bb499a739cd..c850d5ef80a2 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_BLOCK) := elevator.o blk-core.o blk-tag.o blk-sysfs.o \
 
 obj-$(CONFIG_BLK_DEV_BSG)	+= bsg.o
 obj-$(CONFIG_BLK_CGROUP)	+= blk-cgroup.o
+obj-$(CONFIG_BLK_DEV_THROTTLING)	+= blk-throttle.o
 obj-$(CONFIG_IOSCHED_NOOP)	+= noop-iosched.o
 obj-$(CONFIG_IOSCHED_DEADLINE)	+= deadline-iosched.o
 obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
diff --git a/block/blk-core.c b/block/blk-core.c
index 8d07c1b7e701..797d5095eb83 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -382,6 +382,7 @@ void blk_sync_queue(struct request_queue *q)
 	del_timer_sync(&q->unplug_timer);
 	del_timer_sync(&q->timeout);
 	cancel_work_sync(&q->unplug_work);
+	throtl_shutdown_timer_wq(q);
 }
 EXPORT_SYMBOL(blk_sync_queue);
 
@@ -459,6 +460,8 @@ void blk_cleanup_queue(struct request_queue *q)
 	if (q->elevator)
 		elevator_exit(q->elevator);
 
+	blk_throtl_exit(q);
+
 	blk_put_queue(q);
 }
 EXPORT_SYMBOL(blk_cleanup_queue);
@@ -515,6 +518,11 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 		return NULL;
 	}
 
+	if (blk_throtl_init(q)) {
+		kmem_cache_free(blk_requestq_cachep, q);
+		return NULL;
+	}
+
 	setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
 		    laptop_mode_timer_fn, (unsigned long) q);
 	init_timer(&q->unplug_timer);
@@ -1522,6 +1530,15 @@ static inline void __generic_make_request(struct bio *bio)
 			goto end_io;
 		}
 
+		blk_throtl_bio(q, &bio);
+
+		/*
+		 * If bio = NULL, bio has been throttled and will be submitted
+		 * later.
+		 */
+		if (!bio)
+			break;
+
 		trace_block_bio_queue(q, bio);
 
 		ret = q->make_request_fn(q, bio);
@@ -2580,6 +2597,13 @@ int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
 }
 EXPORT_SYMBOL(kblockd_schedule_work);
 
+int kblockd_schedule_delayed_work(struct request_queue *q,
+			struct delayed_work *dwork, unsigned long delay)
+{
+	return queue_delayed_work(kblockd_workqueue, dwork, delay);
+}
+EXPORT_SYMBOL(kblockd_schedule_delayed_work);
+
 int __init blk_dev_init(void)
 {
 	BUILD_BUG_ON(__REQ_NR_BITS > 8 *
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
new file mode 100644
index 000000000000..4b492011e0de
--- /dev/null
+++ b/block/blk-throttle.c
@@ -0,0 +1,909 @@
+/*
+ * Interface for controlling IO bandwidth on a request queue
+ *
+ * Copyright (C) 2010 Vivek Goyal <vgoyal@redhat.com>
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/blktrace_api.h>
+#include "blk-cgroup.h"
+
+/* Max dispatch from a group in 1 round */
+static int throtl_grp_quantum = 8;
+
+/* Total max dispatch from all groups in one round */
+static int throtl_quantum = 32;
+
+/* Throttling is performed over 100ms slice and after that slice is renewed */
+static unsigned long throtl_slice = HZ/10;	/* 100 ms */
+
+struct throtl_rb_root {
+	struct rb_root rb;
+	struct rb_node *left;
+	unsigned int count;
+	unsigned long min_disptime;
+};
+
+#define THROTL_RB_ROOT	(struct throtl_rb_root) { .rb = RB_ROOT, .left = NULL, \
+			.count = 0, .min_disptime = 0}
+
+#define rb_entry_tg(node)	rb_entry((node), struct throtl_grp, rb_node)
+
+struct throtl_grp {
+	/* List of throtl groups on the request queue*/
+	struct hlist_node tg_node;
+
+	/* active throtl group service_tree member */
+	struct rb_node rb_node;
+
+	/*
+	 * Dispatch time in jiffies. This is the estimated time when group
+	 * will unthrottle and is ready to dispatch more bio. It is used as
+	 * key to sort active groups in service tree.
+	 */
+	unsigned long disptime;
+
+	struct blkio_group blkg;
+	atomic_t ref;
+	unsigned int flags;
+
+	/* Two lists for READ and WRITE */
+	struct bio_list bio_lists[2];
+
+	/* Number of queued bios on READ and WRITE lists */
+	unsigned int nr_queued[2];
+
+	/* bytes per second rate limits */
+	uint64_t bps[2];
+
+	/* Number of bytes disptached in current slice */
+	uint64_t bytes_disp[2];
+
+	/* When did we start a new slice */
+	unsigned long slice_start[2];
+	unsigned long slice_end[2];
+};
+
+struct throtl_data
+{
+	/* List of throtl groups */
+	struct hlist_head tg_list;
+
+	/* service tree for active throtl groups */
+	struct throtl_rb_root tg_service_tree;
+
+	struct throtl_grp root_tg;
+	struct request_queue *queue;
+
+	/* Total Number of queued bios on READ and WRITE lists */
+	unsigned int nr_queued[2];
+
+	/*
+	 * number of total undestroyed groups (excluding root group)
+	 */
+	unsigned int nr_undestroyed_grps;
+
+	/* Work for dispatching throttled bios */
+	struct delayed_work throtl_work;
+};
+
+enum tg_state_flags {
+	THROTL_TG_FLAG_on_rr = 0,	/* on round-robin busy list */
+};
+
+#define THROTL_TG_FNS(name)						\
+static inline void throtl_mark_tg_##name(struct throtl_grp *tg)		\
+{									\
+	(tg)->flags |= (1 << THROTL_TG_FLAG_##name);			\
+}									\
+static inline void throtl_clear_tg_##name(struct throtl_grp *tg)	\
+{									\
+	(tg)->flags &= ~(1 << THROTL_TG_FLAG_##name);			\
+}									\
+static inline int throtl_tg_##name(const struct throtl_grp *tg)		\
+{									\
+	return ((tg)->flags & (1 << THROTL_TG_FLAG_##name)) != 0;	\
+}
+
+THROTL_TG_FNS(on_rr);
+
+#define throtl_log_tg(td, tg, fmt, args...)				\
+	blk_add_trace_msg((td)->queue, "throtl %s " fmt,		\
+				blkg_path(&(tg)->blkg), ##args);      	\
+
+#define throtl_log(td, fmt, args...)	\
+	blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)
+
+static inline struct throtl_grp *tg_of_blkg(struct blkio_group *blkg)
+{
+	if (blkg)
+		return container_of(blkg, struct throtl_grp, blkg);
+
+	return NULL;
+}
+
+static inline int total_nr_queued(struct throtl_data *td)
+{
+	return (td->nr_queued[0] + td->nr_queued[1]);
+}
+
+static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
+{
+	atomic_inc(&tg->ref);
+	return tg;
+}
+
+static void throtl_put_tg(struct throtl_grp *tg)
+{
+	BUG_ON(atomic_read(&tg->ref) <= 0);
+	if (!atomic_dec_and_test(&tg->ref))
+		return;
+	kfree(tg);
+}
+
+static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
+			struct cgroup *cgroup)
+{
+	struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
+	struct throtl_grp *tg = NULL;
+	void *key = td;
+	struct backing_dev_info *bdi = &td->queue->backing_dev_info;
+	unsigned int major, minor;
+
+	/*
+	 * TODO: Speed up blkiocg_lookup_group() by maintaining a radix
+	 * tree of blkg (instead of traversing through hash list all
+	 * the time.
+	 */
+	tg = tg_of_blkg(blkiocg_lookup_group(blkcg, key));
+
+	/* Fill in device details for root group */
+	if (tg && !tg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
+		sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
+		tg->blkg.dev = MKDEV(major, minor);
+		goto done;
+	}
+
+	if (tg)
+		goto done;
+
+	tg = kzalloc_node(sizeof(*tg), GFP_ATOMIC, td->queue->node);
+	if (!tg)
+		goto done;
+
+	INIT_HLIST_NODE(&tg->tg_node);
+	RB_CLEAR_NODE(&tg->rb_node);
+	bio_list_init(&tg->bio_lists[0]);
+	bio_list_init(&tg->bio_lists[1]);
+
+	/*
+	 * Take the initial reference that will be released on destroy
+	 * This can be thought of a joint reference by cgroup and
+	 * request queue which will be dropped by either request queue
+	 * exit or cgroup deletion path depending on who is exiting first.
+	 */
+	atomic_set(&tg->ref, 1);
+
+	/* Add group onto cgroup list */
+	sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
+	blkiocg_add_blkio_group(blkcg, &tg->blkg, (void *)td,
+				MKDEV(major, minor), BLKIO_POLICY_THROTL);
+
+	tg->bps[READ] = blkcg_get_read_bps(blkcg, tg->blkg.dev);
+	tg->bps[WRITE] = blkcg_get_write_bps(blkcg, tg->blkg.dev);
+
+	hlist_add_head(&tg->tg_node, &td->tg_list);
+	td->nr_undestroyed_grps++;
+done:
+	return tg;
+}
+
+static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
+{
+	struct cgroup *cgroup;
+	struct throtl_grp *tg = NULL;
+
+	rcu_read_lock();
+	cgroup = task_cgroup(current, blkio_subsys_id);
+	tg = throtl_find_alloc_tg(td, cgroup);
+	if (!tg)
+		tg = &td->root_tg;
+	rcu_read_unlock();
+	return tg;
+}
+
+static struct throtl_grp *throtl_rb_first(struct throtl_rb_root *root)
+{
+	/* Service tree is empty */
+	if (!root->count)
+		return NULL;
+
+	if (!root->left)
+		root->left = rb_first(&root->rb);
+
+	if (root->left)
+		return rb_entry_tg(root->left);
+
+	return NULL;
+}
+
+static void rb_erase_init(struct rb_node *n, struct rb_root *root)
+{
+	rb_erase(n, root);
+	RB_CLEAR_NODE(n);
+}
+
+static void throtl_rb_erase(struct rb_node *n, struct throtl_rb_root *root)
+{
+	if (root->left == n)
+		root->left = NULL;
+	rb_erase_init(n, &root->rb);
+	--root->count;
+}
+
+static void update_min_dispatch_time(struct throtl_rb_root *st)
+{
+	struct throtl_grp *tg;
+
+	tg = throtl_rb_first(st);
+	if (!tg)
+		return;
+
+	st->min_disptime = tg->disptime;
+}
+
+static void
+tg_service_tree_add(struct throtl_rb_root *st, struct throtl_grp *tg)
+{
+	struct rb_node **node = &st->rb.rb_node;
+	struct rb_node *parent = NULL;
+	struct throtl_grp *__tg;
+	unsigned long key = tg->disptime;
+	int left = 1;
+
+	while (*node != NULL) {
+		parent = *node;
+		__tg = rb_entry_tg(parent);
+
+		if (time_before(key, __tg->disptime))
+			node = &parent->rb_left;
+		else {
+			node = &parent->rb_right;
+			left = 0;
+		}
+	}
+
+	if (left)
+		st->left = &tg->rb_node;
+
+	rb_link_node(&tg->rb_node, parent, node);
+	rb_insert_color(&tg->rb_node, &st->rb);
+}
+
+static void __throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+	struct throtl_rb_root *st = &td->tg_service_tree;
+
+	tg_service_tree_add(st, tg);
+	throtl_mark_tg_on_rr(tg);
+	st->count++;
+}
+
+static void throtl_enqueue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+	if (!throtl_tg_on_rr(tg))
+		__throtl_enqueue_tg(td, tg);
+}
+
+static void __throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+	throtl_rb_erase(&tg->rb_node, &td->tg_service_tree);
+	throtl_clear_tg_on_rr(tg);
+}
+
+static void throtl_dequeue_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+	if (throtl_tg_on_rr(tg))
+		__throtl_dequeue_tg(td, tg);
+}
+
+static void throtl_schedule_next_dispatch(struct throtl_data *td)
+{
+	struct throtl_rb_root *st = &td->tg_service_tree;
+
+	/*
+	 * If there are more bios pending, schedule more work.
+	 */
+	if (!total_nr_queued(td))
+		return;
+
+	BUG_ON(!st->count);
+
+	update_min_dispatch_time(st);
+
+	if (time_before_eq(st->min_disptime, jiffies))
+		throtl_schedule_delayed_work(td->queue, 0);
+	else
+		throtl_schedule_delayed_work(td->queue,
+				(st->min_disptime - jiffies));
+}
+
+static inline void
+throtl_start_new_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
+{
+	tg->bytes_disp[rw] = 0;
+	tg->slice_start[rw] = jiffies;
+	tg->slice_end[rw] = jiffies + throtl_slice;
+	throtl_log_tg(td, tg, "[%c] new slice start=%lu end=%lu jiffies=%lu",
+			rw == READ ? 'R' : 'W', tg->slice_start[rw],
+			tg->slice_end[rw], jiffies);
+}
+
+static inline void throtl_extend_slice(struct throtl_data *td,
+		struct throtl_grp *tg, bool rw, unsigned long jiffy_end)
+{
+	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
+	throtl_log_tg(td, tg, "[%c] extend slice start=%lu end=%lu jiffies=%lu",
+			rw == READ ? 'R' : 'W', tg->slice_start[rw],
+			tg->slice_end[rw], jiffies);
+}
+
+/* Determine if previously allocated or extended slice is complete or not */
+static bool
+throtl_slice_used(struct throtl_data *td, struct throtl_grp *tg, bool rw)
+{
+	if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
+		return 0;
+
+	return 1;
+}
+
+/* Trim the used slices and adjust slice start accordingly */
+static inline void
+throtl_trim_slice(struct throtl_data *td, struct throtl_grp *tg, bool rw)
+{
+	unsigned long nr_slices, bytes_trim, time_elapsed;
+
+	BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
+
+	/*
+	 * If bps are unlimited (-1), then time slice don't get
+	 * renewed. Don't try to trim the slice if slice is used. A new
+	 * slice will start when appropriate.
+	 */
+	if (throtl_slice_used(td, tg, rw))
+		return;
+
+	time_elapsed = jiffies - tg->slice_start[rw];
+
+	nr_slices = time_elapsed / throtl_slice;
+
+	if (!nr_slices)
+		return;
+
+	bytes_trim = (tg->bps[rw] * throtl_slice * nr_slices)/HZ;
+
+	if (!bytes_trim)
+		return;
+
+	if (tg->bytes_disp[rw] >= bytes_trim)
+		tg->bytes_disp[rw] -= bytes_trim;
+	else
+		tg->bytes_disp[rw] = 0;
+
+	tg->slice_start[rw] += nr_slices * throtl_slice;
+
+	throtl_log_tg(td, tg, "[%c] trim slice nr=%lu bytes=%lu"
+			" start=%lu end=%lu jiffies=%lu",
+			rw == READ ? 'R' : 'W', nr_slices, bytes_trim,
+			tg->slice_start[rw], tg->slice_end[rw], jiffies);
+}
+
+/*
+ * Returns whether one can dispatch a bio or not. Also returns approx number
+ * of jiffies to wait before this bio is with-in IO rate and can be dispatched
+ */
+static bool tg_may_dispatch(struct throtl_data *td, struct throtl_grp *tg,
+				struct bio *bio, unsigned long *wait)
+{
+	bool rw = bio_data_dir(bio);
+	u64 bytes_allowed, extra_bytes;
+	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
+
+	/*
+	 * Currently whole state machine of group depends on first bio
+	 * queued in the group bio list. So one should not be calling
+	 * this function with a different bio if there are other bios
+	 * queued.
+	 */
+	BUG_ON(tg->nr_queued[rw] && bio != bio_list_peek(&tg->bio_lists[rw]));
+
+	/* If tg->bps = -1, then BW is unlimited */
+	if (tg->bps[rw] == -1) {
+		if (wait)
+			*wait = 0;
+		return 1;
+	}
+
+	/*
+	 * If previous slice expired, start a new one otherwise renew/extend
+	 * existing slice to make sure it is at least throtl_slice interval
+	 * long since now.
+	 */
+	if (throtl_slice_used(td, tg, rw))
+		throtl_start_new_slice(td, tg, rw);
+	else {
+		if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
+			throtl_extend_slice(td, tg, rw, jiffies + throtl_slice);
+	}
+
+	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
+
+	/* Slice has just started. Consider one slice interval */
+	if (!jiffy_elapsed)
+		jiffy_elapsed_rnd = throtl_slice;
+
+	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
+
+	bytes_allowed = (tg->bps[rw] * jiffies_to_msecs(jiffy_elapsed_rnd))
+				/ MSEC_PER_SEC;
+
+	if (tg->bytes_disp[rw] + bio->bi_size <= bytes_allowed) {
+		if (wait)
+			*wait = 0;
+		return 1;
+	}
+
+	/* Calc approx time to dispatch */
+	extra_bytes = tg->bytes_disp[rw] + bio->bi_size - bytes_allowed;
+	jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
+
+	if (!jiffy_wait)
+		jiffy_wait = 1;
+
+	/*
+	 * This wait time is without taking into consideration the rounding
+	 * up we did. Add that time also.
+	 */
+	jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
+
+	if (wait)
+		*wait = jiffy_wait;
+
+	if (time_before(tg->slice_end[rw], jiffies + jiffy_wait))
+		throtl_extend_slice(td, tg, rw, jiffies + jiffy_wait);
+
+	return 0;
+}
+
+static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
+{
+	bool rw = bio_data_dir(bio);
+	bool sync = bio->bi_rw & REQ_SYNC;
+
+	/* Charge the bio to the group */
+	tg->bytes_disp[rw] += bio->bi_size;
+
+	/*
+	 * TODO: This will take blkg->stats_lock. Figure out a way
+	 * to avoid this cost.
+	 */
+	blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size, rw, sync);
+
+}
+
+static void throtl_add_bio_tg(struct throtl_data *td, struct throtl_grp *tg,
+			struct bio *bio)
+{
+	bool rw = bio_data_dir(bio);
+
+	bio_list_add(&tg->bio_lists[rw], bio);
+	/* Take a bio reference on tg */
+	throtl_ref_get_tg(tg);
+	tg->nr_queued[rw]++;
+	td->nr_queued[rw]++;
+	throtl_enqueue_tg(td, tg);
+}
+
+static void tg_update_disptime(struct throtl_data *td, struct throtl_grp *tg)
+{
+	unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
+	struct bio *bio;
+
+	if ((bio = bio_list_peek(&tg->bio_lists[READ])))
+		tg_may_dispatch(td, tg, bio, &read_wait);
+
+	if ((bio = bio_list_peek(&tg->bio_lists[WRITE])))
+		tg_may_dispatch(td, tg, bio, &write_wait);
+
+	min_wait = min(read_wait, write_wait);
+	disptime = jiffies + min_wait;
+
+	/*
+	 * If group is already on active tree, then update dispatch time
+	 * only if it is lesser than existing dispatch time. Otherwise
+	 * always update the dispatch time
+	 */
+
+	if (throtl_tg_on_rr(tg) && time_before(disptime, tg->disptime))
+		return;
+
+	/* Update dispatch time */
+	throtl_dequeue_tg(td, tg);
+	tg->disptime = disptime;
+	throtl_enqueue_tg(td, tg);
+}
+
+static void tg_dispatch_one_bio(struct throtl_data *td, struct throtl_grp *tg,
+				bool rw, struct bio_list *bl)
+{
+	struct bio *bio;
+
+	bio = bio_list_pop(&tg->bio_lists[rw]);
+	tg->nr_queued[rw]--;
+	/* Drop bio reference on tg */
+	throtl_put_tg(tg);
+
+	BUG_ON(td->nr_queued[rw] <= 0);
+	td->nr_queued[rw]--;
+
+	throtl_charge_bio(tg, bio);
+	bio_list_add(bl, bio);
+	bio->bi_rw |= REQ_THROTTLED;
+
+	throtl_trim_slice(td, tg, rw);
+}
+
+static int throtl_dispatch_tg(struct throtl_data *td, struct throtl_grp *tg,
+				struct bio_list *bl)
+{
+	unsigned int nr_reads = 0, nr_writes = 0;
+	unsigned int max_nr_reads = throtl_grp_quantum*3/4;
+	unsigned int max_nr_writes = throtl_grp_quantum - nr_reads;
+	struct bio *bio;
+
+	/* Try to dispatch 75% READS and 25% WRITES */
+
+	while ((bio = bio_list_peek(&tg->bio_lists[READ]))
+		&& tg_may_dispatch(td, tg, bio, NULL)) {
+
+		tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
+		nr_reads++;
+
+		if (nr_reads >= max_nr_reads)
+			break;
+	}
+
+	while ((bio = bio_list_peek(&tg->bio_lists[WRITE]))
+		&& tg_may_dispatch(td, tg, bio, NULL)) {
+
+		tg_dispatch_one_bio(td, tg, bio_data_dir(bio), bl);
+		nr_writes++;
+
+		if (nr_writes >= max_nr_writes)
+			break;
+	}
+
+	return nr_reads + nr_writes;
+}
+
+static int throtl_select_dispatch(struct throtl_data *td, struct bio_list *bl)
+{
+	unsigned int nr_disp = 0;
+	struct throtl_grp *tg;
+	struct throtl_rb_root *st = &td->tg_service_tree;
+
+	while (1) {
+		tg = throtl_rb_first(st);
+
+		if (!tg)
+			break;
+
+		if (time_before(jiffies, tg->disptime))
+			break;
+
+		throtl_dequeue_tg(td, tg);
+
+		nr_disp += throtl_dispatch_tg(td, tg, bl);
+
+		if (tg->nr_queued[0] || tg->nr_queued[1]) {
+			tg_update_disptime(td, tg);
+			throtl_enqueue_tg(td, tg);
+		}
+
+		if (nr_disp >= throtl_quantum)
+			break;
+	}
+
+	return nr_disp;
+}
+
+/* Dispatch throttled bios. Should be called without queue lock held. */
+static int throtl_dispatch(struct request_queue *q)
+{
+	struct throtl_data *td = q->td;
+	unsigned int nr_disp = 0;
+	struct bio_list bio_list_on_stack;
+	struct bio *bio;
+
+	spin_lock_irq(q->queue_lock);
+
+	if (!total_nr_queued(td))
+		goto out;
+
+	bio_list_init(&bio_list_on_stack);
+
+	throtl_log(td, "dispatch nr_queued=%lu read=%u write=%u",
+			total_nr_queued(td), td->nr_queued[READ],
+			td->nr_queued[WRITE]);
+
+	nr_disp = throtl_select_dispatch(td, &bio_list_on_stack);
+
+	if (nr_disp)
+		throtl_log(td, "bios disp=%u", nr_disp);
+
+	throtl_schedule_next_dispatch(td);
+out:
+	spin_unlock_irq(q->queue_lock);
+
+	/*
+	 * If we dispatched some requests, unplug the queue to make sure
+	 * immediate dispatch
+	 */
+	if (nr_disp) {
+		while((bio = bio_list_pop(&bio_list_on_stack)))
+			generic_make_request(bio);
+		blk_unplug(q);
+	}
+	return nr_disp;
+}
+
+void blk_throtl_work(struct work_struct *work)
+{
+	struct throtl_data *td = container_of(work, struct throtl_data,
+					throtl_work.work);
+	struct request_queue *q = td->queue;
+
+	throtl_dispatch(q);
+}
+
+/* Call with queue lock held */
+void throtl_schedule_delayed_work(struct request_queue *q, unsigned long delay)
+{
+
+	struct throtl_data *td = q->td;
+	struct delayed_work *dwork = &td->throtl_work;
+
+	if (total_nr_queued(td) > 0) {
+		/*
+		 * We might have a work scheduled to be executed in future.
+		 * Cancel that and schedule a new one.
+		 */
+		__cancel_delayed_work(dwork);
+		kblockd_schedule_delayed_work(q, dwork, delay);
+		throtl_log(td, "schedule work. delay=%lu jiffies=%lu",
+				delay, jiffies);
+	}
+}
+EXPORT_SYMBOL(throtl_schedule_delayed_work);
+
+static void
+throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)
+{
+	/* Something wrong if we are trying to remove same group twice */
+	BUG_ON(hlist_unhashed(&tg->tg_node));
+
+	hlist_del_init(&tg->tg_node);
+
+	/*
+	 * Put the reference taken at the time of creation so that when all
+	 * queues are gone, group can be destroyed.
+	 */
+	throtl_put_tg(tg);
+	td->nr_undestroyed_grps--;
+}
+
+static void throtl_release_tgs(struct throtl_data *td)
+{
+	struct hlist_node *pos, *n;
+	struct throtl_grp *tg;
+
+	hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) {
+		/*
+		 * If cgroup removal path got to blk_group first and removed
+		 * it from cgroup list, then it will take care of destroying
+		 * cfqg also.
+		 */
+		if (!blkiocg_del_blkio_group(&tg->blkg))
+			throtl_destroy_tg(td, tg);
+	}
+}
+
+static void throtl_td_free(struct throtl_data *td)
+{
+	kfree(td);
+}
+
+/*
+ * Blk cgroup controller notification saying that blkio_group object is being
+ * delinked as associated cgroup object is going away. That also means that
+ * no new IO will come in this group. So get rid of this group as soon as
+ * any pending IO in the group is finished.
+ *
+ * This function is called under rcu_read_lock(). key is the rcu protected
+ * pointer. That means "key" is a valid throtl_data pointer as long as we are
+ * rcu read lock.
+ *
+ * "key" was fetched from blkio_group under blkio_cgroup->lock. That means
+ * it should not be NULL as even if queue was going away, cgroup deltion
+ * path got to it first.
+ */
+void throtl_unlink_blkio_group(void *key, struct blkio_group *blkg)
+{
+	unsigned long flags;
+	struct throtl_data *td = key;
+
+	spin_lock_irqsave(td->queue->queue_lock, flags);
+	throtl_destroy_tg(td, tg_of_blkg(blkg));
+	spin_unlock_irqrestore(td->queue->queue_lock, flags);
+}
+
+static void throtl_update_blkio_group_read_bps (struct blkio_group *blkg,
+			u64 read_bps)
+{
+	tg_of_blkg(blkg)->bps[READ] = read_bps;
+}
+
+static void throtl_update_blkio_group_write_bps (struct blkio_group *blkg,
+			u64 write_bps)
+{
+	tg_of_blkg(blkg)->bps[WRITE] = write_bps;
+}
+
+void throtl_shutdown_timer_wq(struct request_queue *q)
+{
+	struct throtl_data *td = q->td;
+
+	cancel_delayed_work_sync(&td->throtl_work);
+}
+
+static struct blkio_policy_type blkio_policy_throtl = {
+	.ops = {
+		.blkio_unlink_group_fn = throtl_unlink_blkio_group,
+		.blkio_update_group_read_bps_fn =
+					throtl_update_blkio_group_read_bps,
+		.blkio_update_group_write_bps_fn =
+					throtl_update_blkio_group_write_bps,
+	},
+};
+
+int blk_throtl_bio(struct request_queue *q, struct bio **biop)
+{
+	struct throtl_data *td = q->td;
+	struct throtl_grp *tg;
+	struct bio *bio = *biop;
+	bool rw = bio_data_dir(bio), update_disptime = true;
+
+	if (bio->bi_rw & REQ_THROTTLED) {
+		bio->bi_rw &= ~REQ_THROTTLED;
+		return 0;
+	}
+
+	spin_lock_irq(q->queue_lock);
+	tg = throtl_get_tg(td);
+
+	if (tg->nr_queued[rw]) {
+		/*
+		 * There is already another bio queued in same dir. No
+		 * need to update dispatch time.
+		 */
+		update_disptime = false;
+		goto queue_bio;
+	}
+
+	/* Bio is with-in rate limit of group */
+	if (tg_may_dispatch(td, tg, bio, NULL)) {
+		throtl_charge_bio(tg, bio);
+		goto out;
+	}
+
+queue_bio:
+	throtl_log_tg(td, tg, "[%c] bio. disp=%u sz=%u bps=%llu"
+			" queued=%d/%d", rw == READ ? 'R' : 'W',
+			tg->bytes_disp[rw], bio->bi_size, tg->bps[rw],
+			tg->nr_queued[READ], tg->nr_queued[WRITE]);
+
+	throtl_add_bio_tg(q->td, tg, bio);
+	*biop = NULL;
+
+	if (update_disptime) {
+		tg_update_disptime(td, tg);
+		throtl_schedule_next_dispatch(td);
+	}
+
+out:
+	spin_unlock_irq(q->queue_lock);
+	return 0;
+}
+
+int blk_throtl_init(struct request_queue *q)
+{
+	struct throtl_data *td;
+	struct throtl_grp *tg;
+
+	td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
+	if (!td)
+		return -ENOMEM;
+
+	INIT_HLIST_HEAD(&td->tg_list);
+	td->tg_service_tree = THROTL_RB_ROOT;
+
+	/* Init root group */
+	tg = &td->root_tg;
+	INIT_HLIST_NODE(&tg->tg_node);
+	RB_CLEAR_NODE(&tg->rb_node);
+	bio_list_init(&tg->bio_lists[0]);
+	bio_list_init(&tg->bio_lists[1]);
+
+	/* Practically unlimited BW */
+	tg->bps[0] = tg->bps[1] = -1;
+	atomic_set(&tg->ref, 1);
+
+	INIT_DELAYED_WORK(&td->throtl_work, blk_throtl_work);
+
+	rcu_read_lock();
+	blkiocg_add_blkio_group(&blkio_root_cgroup, &tg->blkg, (void *)td,
+					0, BLKIO_POLICY_THROTL);
+	rcu_read_unlock();
+
+	/* Attach throtl data to request queue */
+	td->queue = q;
+	q->td = td;
+	return 0;
+}
+
+void blk_throtl_exit(struct request_queue *q)
+{
+	struct throtl_data *td = q->td;
+	bool wait = false;
+
+	BUG_ON(!td);
+
+	throtl_shutdown_timer_wq(q);
+
+	spin_lock_irq(q->queue_lock);
+	throtl_release_tgs(td);
+	blkiocg_del_blkio_group(&td->root_tg.blkg);
+
+	/* If there are other groups */
+	if (td->nr_undestroyed_grps >= 1)
+		wait = true;
+
+	spin_unlock_irq(q->queue_lock);
+
+	/*
+	 * Wait for tg->blkg->key accessors to exit their grace periods.
+	 * Do this wait only if there are other undestroyed groups out
+	 * there (other than root group). This can happen if cgroup deletion
+	 * path claimed the responsibility of cleaning up a group before
+	 * queue cleanup code get to the group.
+	 *
+	 * Do not call synchronize_rcu() unconditionally as there are drivers
+	 * which create/delete request queue hundreds of times during scan/boot
+	 * and synchronize_rcu() can take significant time and slow down boot.
+	 */
+	if (wait)
+		synchronize_rcu();
+	throtl_td_free(td);
+}
+
+static int __init throtl_init(void)
+{
+	blkio_policy_register(&blkio_policy_throtl);
+	return 0;
+}
+
+module_init(throtl_init);