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>

1 files changed, 909 insertions, 0 deletions

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);