Merge tag 'clk-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-stable.git] / block / blk-throttle.c

// SPDX-License-Identifier: GPL-2.0
/*
 * 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.h"
#include "blk-cgroup-rwstat.h"
#include "blk-stat.h"
#include "blk-throttle.h"

/* Max dispatch from a group in 1 round */
#define THROTL_GRP_QUANTUM 8

/* Total max dispatch from all groups in one round */
#define THROTL_QUANTUM 32

/* Throttling is performed over a slice and after that slice is renewed */
#define DFL_THROTL_SLICE_HD (HZ / 10)
#define DFL_THROTL_SLICE_SSD (HZ / 50)
#define MAX_THROTL_SLICE (HZ)

/* A workqueue to queue throttle related work */
static struct workqueue_struct *kthrotld_workqueue;

#define rb_entry_tg(node)       rb_entry((node), struct throtl_grp, rb_node)

struct throtl_data
{
        /* service tree for active throtl groups */
        struct throtl_service_queue service_queue;

        struct request_queue *queue;

        /* Total Number of queued bios on READ and WRITE lists */
        unsigned int nr_queued[2];

        unsigned int throtl_slice;

        /* Work for dispatching throttled bios */
        struct work_struct dispatch_work;

        bool track_bio_latency;
};

static void throtl_pending_timer_fn(struct timer_list *t);

static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
{
        return pd_to_blkg(&tg->pd);
}

/**
 * sq_to_tg - return the throl_grp the specified service queue belongs to
 * @sq: the throtl_service_queue of interest
 *
 * Return the throtl_grp @sq belongs to.  If @sq is the top-level one
 * embedded in throtl_data, %NULL is returned.
 */
static struct throtl_grp *sq_to_tg(struct throtl_service_queue *sq)
{
        if (sq && sq->parent_sq)
                return container_of(sq, struct throtl_grp, service_queue);
        else
                return NULL;
}

/**
 * sq_to_td - return throtl_data the specified service queue belongs to
 * @sq: the throtl_service_queue of interest
 *
 * A service_queue can be embedded in either a throtl_grp or throtl_data.
 * Determine the associated throtl_data accordingly and return it.
 */
static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
{
        struct throtl_grp *tg = sq_to_tg(sq);

        if (tg)
                return tg->td;
        else
                return container_of(sq, struct throtl_data, service_queue);
}

static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
{
        struct blkcg_gq *blkg = tg_to_blkg(tg);

        if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
                return U64_MAX;

        return tg->bps[rw];
}

static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
{
        struct blkcg_gq *blkg = tg_to_blkg(tg);

        if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
                return UINT_MAX;

        return tg->iops[rw];
}

/**
 * throtl_log - log debug message via blktrace
 * @sq: the service_queue being reported
 * @fmt: printf format string
 * @args: printf args
 *
 * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
 * throtl_grp; otherwise, just "throtl".
 */
#define throtl_log(sq, fmt, args...)    do {                            \
        struct throtl_grp *__tg = sq_to_tg((sq));                       \
        struct throtl_data *__td = sq_to_td((sq));                      \
                                                                        \
        (void)__td;                                                     \
        if (likely(!blk_trace_note_message_enabled(__td->queue)))       \
                break;                                                  \
        if ((__tg)) {                                                   \
                blk_add_cgroup_trace_msg(__td->queue,                   \
                        &tg_to_blkg(__tg)->blkcg->css, "throtl " fmt, ##args);\
        } else {                                                        \
                blk_add_trace_msg(__td->queue, "throtl " fmt, ##args);  \
        }                                                               \
} while (0)

static inline unsigned int throtl_bio_data_size(struct bio *bio)
{
        /* assume it's one sector */
        if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
                return 512;
        return bio->bi_iter.bi_size;
}

static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
{
        INIT_LIST_HEAD(&qn->node);
        bio_list_init(&qn->bios);
        qn->tg = tg;
}

/**
 * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it
 * @bio: bio being added
 * @qn: qnode to add bio to
 * @queued: the service_queue->queued[] list @qn belongs to
 *
 * Add @bio to @qn and put @qn on @queued if it's not already on.
 * @qn->tg's reference count is bumped when @qn is activated.  See the
 * comment on top of throtl_qnode definition for details.
 */
static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn,
                                 struct list_head *queued)
{
        bio_list_add(&qn->bios, bio);
        if (list_empty(&qn->node)) {
                list_add_tail(&qn->node, queued);
                blkg_get(tg_to_blkg(qn->tg));
        }
}

/**
 * throtl_peek_queued - peek the first bio on a qnode list
 * @queued: the qnode list to peek
 */
static struct bio *throtl_peek_queued(struct list_head *queued)
{
        struct throtl_qnode *qn;
        struct bio *bio;

        if (list_empty(queued))
                return NULL;

        qn = list_first_entry(queued, struct throtl_qnode, node);
        bio = bio_list_peek(&qn->bios);
        WARN_ON_ONCE(!bio);
        return bio;
}

/**
 * throtl_pop_queued - pop the first bio form a qnode list
 * @queued: the qnode list to pop a bio from
 * @tg_to_put: optional out argument for throtl_grp to put
 *
 * Pop the first bio from the qnode list @queued.  After popping, the first
 * qnode is removed from @queued if empty or moved to the end of @queued so
 * that the popping order is round-robin.
 *
 * When the first qnode is removed, its associated throtl_grp should be put
 * too.  If @tg_to_put is NULL, this function automatically puts it;
 * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is
 * responsible for putting it.
 */
static struct bio *throtl_pop_queued(struct list_head *queued,
                                     struct throtl_grp **tg_to_put)
{
        struct throtl_qnode *qn;
        struct bio *bio;

        if (list_empty(queued))
                return NULL;

        qn = list_first_entry(queued, struct throtl_qnode, node);
        bio = bio_list_pop(&qn->bios);
        WARN_ON_ONCE(!bio);

        if (bio_list_empty(&qn->bios)) {
                list_del_init(&qn->node);
                if (tg_to_put)
                        *tg_to_put = qn->tg;
                else
                        blkg_put(tg_to_blkg(qn->tg));
        } else {
                list_move_tail(&qn->node, queued);
        }

        return bio;
}

/* init a service_queue, assumes the caller zeroed it */
static void throtl_service_queue_init(struct throtl_service_queue *sq)
{
        INIT_LIST_HEAD(&sq->queued[READ]);
        INIT_LIST_HEAD(&sq->queued[WRITE]);
        sq->pending_tree = RB_ROOT_CACHED;
        timer_setup(&sq->pending_timer, throtl_pending_timer_fn, 0);
}

static struct blkg_policy_data *throtl_pd_alloc(struct gendisk *disk,
                struct blkcg *blkcg, gfp_t gfp)
{
        struct throtl_grp *tg;
        int rw;

        tg = kzalloc_node(sizeof(*tg), gfp, disk->node_id);
        if (!tg)
                return NULL;

        if (blkg_rwstat_init(&tg->stat_bytes, gfp))
                goto err_free_tg;

        if (blkg_rwstat_init(&tg->stat_ios, gfp))
                goto err_exit_stat_bytes;

        throtl_service_queue_init(&tg->service_queue);

        for (rw = READ; rw <= WRITE; rw++) {
                throtl_qnode_init(&tg->qnode_on_self[rw], tg);
                throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
        }

        RB_CLEAR_NODE(&tg->rb_node);
        tg->bps[READ] = U64_MAX;
        tg->bps[WRITE] = U64_MAX;
        tg->iops[READ] = UINT_MAX;
        tg->iops[WRITE] = UINT_MAX;

        return &tg->pd;

err_exit_stat_bytes:
        blkg_rwstat_exit(&tg->stat_bytes);
err_free_tg:
        kfree(tg);
        return NULL;
}

static void throtl_pd_init(struct blkg_policy_data *pd)
{
        struct throtl_grp *tg = pd_to_tg(pd);
        struct blkcg_gq *blkg = tg_to_blkg(tg);
        struct throtl_data *td = blkg->q->td;
        struct throtl_service_queue *sq = &tg->service_queue;

        /*
         * If on the default hierarchy, we switch to properly hierarchical
         * behavior where limits on a given throtl_grp are applied to the
         * whole subtree rather than just the group itself.  e.g. If 16M
         * read_bps limit is set on a parent group, summary bps of
         * parent group and its subtree groups can't exceed 16M for the
         * device.
         *
         * If not on the default hierarchy, the broken flat hierarchy
         * behavior is retained where all throtl_grps are treated as if
         * they're all separate root groups right below throtl_data.
         * Limits of a group don't interact with limits of other groups
         * regardless of the position of the group in the hierarchy.
         */
        sq->parent_sq = &td->service_queue;
        if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
                sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
        tg->td = td;
}

/*
 * Set has_rules[] if @tg or any of its parents have limits configured.
 * This doesn't require walking up to the top of the hierarchy as the
 * parent's has_rules[] is guaranteed to be correct.
 */
static void tg_update_has_rules(struct throtl_grp *tg)
{
        struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
        int rw;

        for (rw = READ; rw <= WRITE; rw++) {
                tg->has_rules_iops[rw] =
                        (parent_tg && parent_tg->has_rules_iops[rw]) ||
                        tg_iops_limit(tg, rw) != UINT_MAX;
                tg->has_rules_bps[rw] =
                        (parent_tg && parent_tg->has_rules_bps[rw]) ||
                        tg_bps_limit(tg, rw) != U64_MAX;
        }
}

static void throtl_pd_online(struct blkg_policy_data *pd)
{
        struct throtl_grp *tg = pd_to_tg(pd);
        /*
         * We don't want new groups to escape the limits of its ancestors.
         * Update has_rules[] after a new group is brought online.
         */
        tg_update_has_rules(tg);
}

static void throtl_pd_free(struct blkg_policy_data *pd)
{
        struct throtl_grp *tg = pd_to_tg(pd);

        del_timer_sync(&tg->service_queue.pending_timer);
        blkg_rwstat_exit(&tg->stat_bytes);
        blkg_rwstat_exit(&tg->stat_ios);
        kfree(tg);
}

static struct throtl_grp *
throtl_rb_first(struct throtl_service_queue *parent_sq)
{
        struct rb_node *n;

        n = rb_first_cached(&parent_sq->pending_tree);
        WARN_ON_ONCE(!n);
        if (!n)
                return NULL;
        return rb_entry_tg(n);
}

static void throtl_rb_erase(struct rb_node *n,
                            struct throtl_service_queue *parent_sq)
{
        rb_erase_cached(n, &parent_sq->pending_tree);
        RB_CLEAR_NODE(n);
}

static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
{
        struct throtl_grp *tg;

        tg = throtl_rb_first(parent_sq);
        if (!tg)
                return;

        parent_sq->first_pending_disptime = tg->disptime;
}

static void tg_service_queue_add(struct throtl_grp *tg)
{
        struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
        struct rb_node **node = &parent_sq->pending_tree.rb_root.rb_node;
        struct rb_node *parent = NULL;
        struct throtl_grp *__tg;
        unsigned long key = tg->disptime;
        bool leftmost = true;

        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;
                        leftmost = false;
                }
        }

        rb_link_node(&tg->rb_node, parent, node);
        rb_insert_color_cached(&tg->rb_node, &parent_sq->pending_tree,
                               leftmost);
}

static void throtl_enqueue_tg(struct throtl_grp *tg)
{
        if (!(tg->flags & THROTL_TG_PENDING)) {
                tg_service_queue_add(tg);
                tg->flags |= THROTL_TG_PENDING;
                tg->service_queue.parent_sq->nr_pending++;
        }
}

static void throtl_dequeue_tg(struct throtl_grp *tg)
{
        if (tg->flags & THROTL_TG_PENDING) {
                struct throtl_service_queue *parent_sq =
                        tg->service_queue.parent_sq;

                throtl_rb_erase(&tg->rb_node, parent_sq);
                --parent_sq->nr_pending;
                tg->flags &= ~THROTL_TG_PENDING;
        }
}

/* Call with queue lock held */
static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
                                          unsigned long expires)
{
        unsigned long max_expire = jiffies + 8 * sq_to_td(sq)->throtl_slice;

        /*
         * Since we are adjusting the throttle limit dynamically, the sleep
         * time calculated according to previous limit might be invalid. It's
         * possible the cgroup sleep time is very long and no other cgroups
         * have IO running so notify the limit changes. Make sure the cgroup
         * doesn't sleep too long to avoid the missed notification.
         */
        if (time_after(expires, max_expire))
                expires = max_expire;
        mod_timer(&sq->pending_timer, expires);
        throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
                   expires - jiffies, jiffies);
}

/**
 * throtl_schedule_next_dispatch - schedule the next dispatch cycle
 * @sq: the service_queue to schedule dispatch for
 * @force: force scheduling
 *
 * Arm @sq->pending_timer so that the next dispatch cycle starts on the
 * dispatch time of the first pending child.  Returns %true if either timer
 * is armed or there's no pending child left.  %false if the current
 * dispatch window is still open and the caller should continue
 * dispatching.
 *
 * If @force is %true, the dispatch timer is always scheduled and this
 * function is guaranteed to return %true.  This is to be used when the
 * caller can't dispatch itself and needs to invoke pending_timer
 * unconditionally.  Note that forced scheduling is likely to induce short
 * delay before dispatch starts even if @sq->first_pending_disptime is not
 * in the future and thus shouldn't be used in hot paths.
 */
static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
                                          bool force)
{
        /* any pending children left? */
        if (!sq->nr_pending)
                return true;

        update_min_dispatch_time(sq);

        /* is the next dispatch time in the future? */
        if (force || time_after(sq->first_pending_disptime, jiffies)) {
                throtl_schedule_pending_timer(sq, sq->first_pending_disptime);
                return true;
        }

        /* tell the caller to continue dispatching */
        return false;
}

static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
                bool rw, unsigned long start)
{
        tg->bytes_disp[rw] = 0;
        tg->io_disp[rw] = 0;
        tg->carryover_bytes[rw] = 0;
        tg->carryover_ios[rw] = 0;

        /*
         * Previous slice has expired. We must have trimmed it after last
         * bio dispatch. That means since start of last slice, we never used
         * that bandwidth. Do try to make use of that bandwidth while giving
         * credit.
         */
        if (time_after(start, tg->slice_start[rw]))
                tg->slice_start[rw] = start;

        tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
        throtl_log(&tg->service_queue,
                   "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
                   rw == READ ? 'R' : 'W', tg->slice_start[rw],
                   tg->slice_end[rw], jiffies);
}

static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw,
                                          bool clear_carryover)
{
        tg->bytes_disp[rw] = 0;
        tg->io_disp[rw] = 0;
        tg->slice_start[rw] = jiffies;
        tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
        if (clear_carryover) {
                tg->carryover_bytes[rw] = 0;
                tg->carryover_ios[rw] = 0;
        }

        throtl_log(&tg->service_queue,
                   "[%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_set_slice_end(struct throtl_grp *tg, bool rw,
                                        unsigned long jiffy_end)
{
        tg->slice_end[rw] = roundup(jiffy_end, tg->td->throtl_slice);
}

static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
                                       unsigned long jiffy_end)
{
        throtl_set_slice_end(tg, rw, jiffy_end);
        throtl_log(&tg->service_queue,
                   "[%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_grp *tg, bool rw)
{
        if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
                return false;

        return true;
}

static unsigned int calculate_io_allowed(u32 iops_limit,
                                         unsigned long jiffy_elapsed)
{
        unsigned int io_allowed;
        u64 tmp;

        /*
         * jiffy_elapsed should not be a big value as minimum iops can be
         * 1 then at max jiffy elapsed should be equivalent of 1 second as we
         * will allow dispatch after 1 second and after that slice should
         * have been trimmed.
         */

        tmp = (u64)iops_limit * jiffy_elapsed;
        do_div(tmp, HZ);

        if (tmp > UINT_MAX)
                io_allowed = UINT_MAX;
        else
                io_allowed = tmp;

        return io_allowed;
}

static u64 calculate_bytes_allowed(u64 bps_limit, unsigned long jiffy_elapsed)
{
        /*
         * Can result be wider than 64 bits?
         * We check against 62, not 64, due to ilog2 truncation.
         */
        if (ilog2(bps_limit) + ilog2(jiffy_elapsed) - ilog2(HZ) > 62)
                return U64_MAX;
        return mul_u64_u64_div_u64(bps_limit, (u64)jiffy_elapsed, (u64)HZ);
}

/* Trim the used slices and adjust slice start accordingly */
static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
{
        unsigned long time_elapsed;
        long long bytes_trim;
        int io_trim;

        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(tg, rw))
                return;

        /*
         * A bio has been dispatched. Also adjust slice_end. It might happen
         * that initially cgroup limit was very low resulting in high
         * slice_end, but later limit was bumped up and bio was dispatched
         * sooner, then we need to reduce slice_end. A high bogus slice_end
         * is bad because it does not allow new slice to start.
         */

        throtl_set_slice_end(tg, rw, jiffies + tg->td->throtl_slice);

        time_elapsed = rounddown(jiffies - tg->slice_start[rw],
                                 tg->td->throtl_slice);
        if (!time_elapsed)
                return;

        bytes_trim = calculate_bytes_allowed(tg_bps_limit(tg, rw),
                                             time_elapsed) +
                     tg->carryover_bytes[rw];
        io_trim = calculate_io_allowed(tg_iops_limit(tg, rw), time_elapsed) +
                  tg->carryover_ios[rw];
        if (bytes_trim <= 0 && io_trim <= 0)
                return;

        tg->carryover_bytes[rw] = 0;
        if ((long long)tg->bytes_disp[rw] >= bytes_trim)
                tg->bytes_disp[rw] -= bytes_trim;
        else
                tg->bytes_disp[rw] = 0;

        tg->carryover_ios[rw] = 0;
        if ((int)tg->io_disp[rw] >= io_trim)
                tg->io_disp[rw] -= io_trim;
        else
                tg->io_disp[rw] = 0;

        tg->slice_start[rw] += time_elapsed;

        throtl_log(&tg->service_queue,
                   "[%c] trim slice nr=%lu bytes=%lld io=%d start=%lu end=%lu jiffies=%lu",
                   rw == READ ? 'R' : 'W', time_elapsed / tg->td->throtl_slice,
                   bytes_trim, io_trim, tg->slice_start[rw], tg->slice_end[rw],
                   jiffies);
}

static void __tg_update_carryover(struct throtl_grp *tg, bool rw)
{
        unsigned long jiffy_elapsed = jiffies - tg->slice_start[rw];
        u64 bps_limit = tg_bps_limit(tg, rw);
        u32 iops_limit = tg_iops_limit(tg, rw);

        /*
         * If config is updated while bios are still throttled, calculate and
         * accumulate how many bytes/ios are waited across changes. And
         * carryover_bytes/ios will be used to calculate new wait time under new
         * configuration.
         */
        if (bps_limit != U64_MAX)
                tg->carryover_bytes[rw] +=
                        calculate_bytes_allowed(bps_limit, jiffy_elapsed) -
                        tg->bytes_disp[rw];
        if (iops_limit != UINT_MAX)
                tg->carryover_ios[rw] +=
                        calculate_io_allowed(iops_limit, jiffy_elapsed) -
                        tg->io_disp[rw];
}

static void tg_update_carryover(struct throtl_grp *tg)
{
        if (tg->service_queue.nr_queued[READ])
                __tg_update_carryover(tg, READ);
        if (tg->service_queue.nr_queued[WRITE])
                __tg_update_carryover(tg, WRITE);

        /* see comments in struct throtl_grp for meaning of these fields. */
        throtl_log(&tg->service_queue, "%s: %lld %lld %d %d\n", __func__,
                   tg->carryover_bytes[READ], tg->carryover_bytes[WRITE],
                   tg->carryover_ios[READ], tg->carryover_ios[WRITE]);
}

static unsigned long tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio,
                                 u32 iops_limit)
{
        bool rw = bio_data_dir(bio);
        int io_allowed;
        unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;

        if (iops_limit == UINT_MAX) {
                return 0;
        }

        jiffy_elapsed = jiffies - tg->slice_start[rw];

        /* Round up to the next throttle slice, wait time must be nonzero */
        jiffy_elapsed_rnd = roundup(jiffy_elapsed + 1, tg->td->throtl_slice);
        io_allowed = calculate_io_allowed(iops_limit, jiffy_elapsed_rnd) +
                     tg->carryover_ios[rw];
        if (io_allowed > 0 && tg->io_disp[rw] + 1 <= io_allowed)
                return 0;

        /* Calc approx time to dispatch */
        jiffy_wait = jiffy_elapsed_rnd - jiffy_elapsed;

        /* make sure at least one io can be dispatched after waiting */
        jiffy_wait = max(jiffy_wait, HZ / iops_limit + 1);
        return jiffy_wait;
}

static unsigned long tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio,
                                u64 bps_limit)
{
        bool rw = bio_data_dir(bio);
        long long bytes_allowed;
        u64 extra_bytes;
        unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
        unsigned int bio_size = throtl_bio_data_size(bio);

        /* no need to throttle if this bio's bytes have been accounted */
        if (bps_limit == U64_MAX || bio_flagged(bio, BIO_BPS_THROTTLED)) {
                return 0;
        }

        jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];

        /* Slice has just started. Consider one slice interval */
        if (!jiffy_elapsed)
                jiffy_elapsed_rnd = tg->td->throtl_slice;

        jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
        bytes_allowed = calculate_bytes_allowed(bps_limit, jiffy_elapsed_rnd) +
                        tg->carryover_bytes[rw];
        if (bytes_allowed > 0 && tg->bytes_disp[rw] + bio_size <= bytes_allowed)
                return 0;

        /* Calc approx time to dispatch */
        extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed;
        jiffy_wait = div64_u64(extra_bytes * HZ, bps_limit);

        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);
        return jiffy_wait;
}

/*
 * 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_grp *tg, struct bio *bio,
                            unsigned long *wait)
{
        bool rw = bio_data_dir(bio);
        unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
        u64 bps_limit = tg_bps_limit(tg, rw);
        u32 iops_limit = tg_iops_limit(tg, rw);

        /*
         * 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->service_queue.nr_queued[rw] &&
               bio != throtl_peek_queued(&tg->service_queue.queued[rw]));

        /* If tg->bps = -1, then BW is unlimited */
        if ((bps_limit == U64_MAX && iops_limit == UINT_MAX) ||
            tg->flags & THROTL_TG_CANCELING) {
                if (wait)
                        *wait = 0;
                return true;
        }

        /*
         * 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. New slice is started only for empty throttle group.
         * If there is queued bio, that means there should be an active
         * slice and it should be extended instead.
         */
        if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
                throtl_start_new_slice(tg, rw, true);
        else {
                if (time_before(tg->slice_end[rw],
                    jiffies + tg->td->throtl_slice))
                        throtl_extend_slice(tg, rw,
                                jiffies + tg->td->throtl_slice);
        }

        bps_wait = tg_within_bps_limit(tg, bio, bps_limit);
        iops_wait = tg_within_iops_limit(tg, bio, iops_limit);
        if (bps_wait + iops_wait == 0) {
                if (wait)
                        *wait = 0;
                return true;
        }

        max_wait = max(bps_wait, iops_wait);

        if (wait)
                *wait = max_wait;

        if (time_before(tg->slice_end[rw], jiffies + max_wait))
                throtl_extend_slice(tg, rw, jiffies + max_wait);

        return false;
}

static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
{
        bool rw = bio_data_dir(bio);
        unsigned int bio_size = throtl_bio_data_size(bio);

        /* Charge the bio to the group */
        if (!bio_flagged(bio, BIO_BPS_THROTTLED)) {
                tg->bytes_disp[rw] += bio_size;
                tg->last_bytes_disp[rw] += bio_size;
        }

        tg->io_disp[rw]++;
        tg->last_io_disp[rw]++;
}

/**
 * throtl_add_bio_tg - add a bio to the specified throtl_grp
 * @bio: bio to add
 * @qn: qnode to use
 * @tg: the target throtl_grp
 *
 * Add @bio to @tg's service_queue using @qn.  If @qn is not specified,
 * tg->qnode_on_self[] is used.
 */
static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
                              struct throtl_grp *tg)
{
        struct throtl_service_queue *sq = &tg->service_queue;
        bool rw = bio_data_dir(bio);

        if (!qn)
                qn = &tg->qnode_on_self[rw];

        /*
         * If @tg doesn't currently have any bios queued in the same
         * direction, queueing @bio can change when @tg should be
         * dispatched.  Mark that @tg was empty.  This is automatically
         * cleared on the next tg_update_disptime().
         */
        if (!sq->nr_queued[rw])
                tg->flags |= THROTL_TG_WAS_EMPTY;

        throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);

        sq->nr_queued[rw]++;
        throtl_enqueue_tg(tg);
}

static void tg_update_disptime(struct throtl_grp *tg)
{
        struct throtl_service_queue *sq = &tg->service_queue;
        unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
        struct bio *bio;

        bio = throtl_peek_queued(&sq->queued[READ]);
        if (bio)
                tg_may_dispatch(tg, bio, &read_wait);

        bio = throtl_peek_queued(&sq->queued[WRITE]);
        if (bio)
                tg_may_dispatch(tg, bio, &write_wait);

        min_wait = min(read_wait, write_wait);
        disptime = jiffies + min_wait;

        /* Update dispatch time */
        throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
        tg->disptime = disptime;
        tg_service_queue_add(tg);

        /* see throtl_add_bio_tg() */
        tg->flags &= ~THROTL_TG_WAS_EMPTY;
}

static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
                                        struct throtl_grp *parent_tg, bool rw)
{
        if (throtl_slice_used(parent_tg, rw)) {
                throtl_start_new_slice_with_credit(parent_tg, rw,
                                child_tg->slice_start[rw]);
        }

}

static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
{
        struct throtl_service_queue *sq = &tg->service_queue;
        struct throtl_service_queue *parent_sq = sq->parent_sq;
        struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
        struct throtl_grp *tg_to_put = NULL;
        struct bio *bio;

        /*
         * @bio is being transferred from @tg to @parent_sq.  Popping a bio
         * from @tg may put its reference and @parent_sq might end up
         * getting released prematurely.  Remember the tg to put and put it
         * after @bio is transferred to @parent_sq.
         */
        bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
        sq->nr_queued[rw]--;

        throtl_charge_bio(tg, bio);

        /*
         * If our parent is another tg, we just need to transfer @bio to
         * the parent using throtl_add_bio_tg().  If our parent is
         * @td->service_queue, @bio is ready to be issued.  Put it on its
         * bio_lists[] and decrease total number queued.  The caller is
         * responsible for issuing these bios.
         */
        if (parent_tg) {
                throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
                start_parent_slice_with_credit(tg, parent_tg, rw);
        } else {
                bio_set_flag(bio, BIO_BPS_THROTTLED);
                throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
                                     &parent_sq->queued[rw]);
                BUG_ON(tg->td->nr_queued[rw] <= 0);
                tg->td->nr_queued[rw]--;
        }

        throtl_trim_slice(tg, rw);

        if (tg_to_put)
                blkg_put(tg_to_blkg(tg_to_put));
}

static int throtl_dispatch_tg(struct throtl_grp *tg)
{
        struct throtl_service_queue *sq = &tg->service_queue;
        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 - max_nr_reads;
        struct bio *bio;

        /* Try to dispatch 75% READS and 25% WRITES */

        while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
               tg_may_dispatch(tg, bio, NULL)) {

                tg_dispatch_one_bio(tg, READ);
                nr_reads++;

                if (nr_reads >= max_nr_reads)
                        break;
        }

        while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
               tg_may_dispatch(tg, bio, NULL)) {

                tg_dispatch_one_bio(tg, WRITE);
                nr_writes++;

                if (nr_writes >= max_nr_writes)
                        break;
        }

        return nr_reads + nr_writes;
}

static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
{
        unsigned int nr_disp = 0;

        while (1) {
                struct throtl_grp *tg;
                struct throtl_service_queue *sq;

                if (!parent_sq->nr_pending)
                        break;

                tg = throtl_rb_first(parent_sq);
                if (!tg)
                        break;

                if (time_before(jiffies, tg->disptime))
                        break;

                nr_disp += throtl_dispatch_tg(tg);

                sq = &tg->service_queue;
                if (sq->nr_queued[READ] || sq->nr_queued[WRITE])
                        tg_update_disptime(tg);
                else
                        throtl_dequeue_tg(tg);

                if (nr_disp >= THROTL_QUANTUM)
                        break;
        }

        return nr_disp;
}

/**
 * throtl_pending_timer_fn - timer function for service_queue->pending_timer
 * @t: the pending_timer member of the throtl_service_queue being serviced
 *
 * This timer is armed when a child throtl_grp with active bio's become
 * pending and queued on the service_queue's pending_tree and expires when
 * the first child throtl_grp should be dispatched.  This function
 * dispatches bio's from the children throtl_grps to the parent
 * service_queue.
 *
 * If the parent's parent is another throtl_grp, dispatching is propagated
 * by either arming its pending_timer or repeating dispatch directly.  If
 * the top-level service_tree is reached, throtl_data->dispatch_work is
 * kicked so that the ready bio's are issued.
 */
static void throtl_pending_timer_fn(struct timer_list *t)
{
        struct throtl_service_queue *sq = from_timer(sq, t, pending_timer);
        struct throtl_grp *tg = sq_to_tg(sq);
        struct throtl_data *td = sq_to_td(sq);
        struct throtl_service_queue *parent_sq;
        struct request_queue *q;
        bool dispatched;
        int ret;

        /* throtl_data may be gone, so figure out request queue by blkg */
        if (tg)
                q = tg->pd.blkg->q;
        else
                q = td->queue;

        spin_lock_irq(&q->queue_lock);

        if (!q->root_blkg)
                goto out_unlock;

again:
        parent_sq = sq->parent_sq;
        dispatched = false;

        while (true) {
                throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
                           sq->nr_queued[READ] + sq->nr_queued[WRITE],
                           sq->nr_queued[READ], sq->nr_queued[WRITE]);

                ret = throtl_select_dispatch(sq);
                if (ret) {
                        throtl_log(sq, "bios disp=%u", ret);
                        dispatched = true;
                }

                if (throtl_schedule_next_dispatch(sq, false))
                        break;

                /* this dispatch windows is still open, relax and repeat */
                spin_unlock_irq(&q->queue_lock);
                cpu_relax();
                spin_lock_irq(&q->queue_lock);
        }

        if (!dispatched)
                goto out_unlock;

        if (parent_sq) {
                /* @parent_sq is another throl_grp, propagate dispatch */
                if (tg->flags & THROTL_TG_WAS_EMPTY) {
                        tg_update_disptime(tg);
                        if (!throtl_schedule_next_dispatch(parent_sq, false)) {
                                /* window is already open, repeat dispatching */
                                sq = parent_sq;
                                tg = sq_to_tg(sq);
                                goto again;
                        }
                }
        } else {
                /* reached the top-level, queue issuing */
                queue_work(kthrotld_workqueue, &td->dispatch_work);
        }
out_unlock:
        spin_unlock_irq(&q->queue_lock);
}

/**
 * blk_throtl_dispatch_work_fn - work function for throtl_data->dispatch_work
 * @work: work item being executed
 *
 * This function is queued for execution when bios reach the bio_lists[]
 * of throtl_data->service_queue.  Those bios are ready and issued by this
 * function.
 */
static void blk_throtl_dispatch_work_fn(struct work_struct *work)
{
        struct throtl_data *td = container_of(work, struct throtl_data,
                                              dispatch_work);
        struct throtl_service_queue *td_sq = &td->service_queue;
        struct request_queue *q = td->queue;
        struct bio_list bio_list_on_stack;
        struct bio *bio;
        struct blk_plug plug;
        int rw;

        bio_list_init(&bio_list_on_stack);

        spin_lock_irq(&q->queue_lock);
        for (rw = READ; rw <= WRITE; rw++)
                while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
                        bio_list_add(&bio_list_on_stack, bio);
        spin_unlock_irq(&q->queue_lock);

        if (!bio_list_empty(&bio_list_on_stack)) {
                blk_start_plug(&plug);
                while ((bio = bio_list_pop(&bio_list_on_stack)))
                        submit_bio_noacct_nocheck(bio);
                blk_finish_plug(&plug);
        }
}

static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
                              int off)
{
        struct throtl_grp *tg = pd_to_tg(pd);
        u64 v = *(u64 *)((void *)tg + off);

        if (v == U64_MAX)
                return 0;
        return __blkg_prfill_u64(sf, pd, v);
}

static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
                               int off)
{
        struct throtl_grp *tg = pd_to_tg(pd);
        unsigned int v = *(unsigned int *)((void *)tg + off);

        if (v == UINT_MAX)
                return 0;
        return __blkg_prfill_u64(sf, pd, v);
}

static int tg_print_conf_u64(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_u64,
                          &blkcg_policy_throtl, seq_cft(sf)->private, false);
        return 0;
}

static int tg_print_conf_uint(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_uint,
                          &blkcg_policy_throtl, seq_cft(sf)->private, false);
        return 0;
}

static void tg_conf_updated(struct throtl_grp *tg, bool global)
{
        struct throtl_service_queue *sq = &tg->service_queue;
        struct cgroup_subsys_state *pos_css;
        struct blkcg_gq *blkg;

        throtl_log(&tg->service_queue,
                   "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
                   tg_bps_limit(tg, READ), tg_bps_limit(tg, WRITE),
                   tg_iops_limit(tg, READ), tg_iops_limit(tg, WRITE));

        rcu_read_lock();
        /*
         * Update has_rules[] flags for the updated tg's subtree.  A tg is
         * considered to have rules if either the tg itself or any of its
         * ancestors has rules.  This identifies groups without any
         * restrictions in the whole hierarchy and allows them to bypass
         * blk-throttle.
         */
        blkg_for_each_descendant_pre(blkg, pos_css,
                        global ? tg->td->queue->root_blkg : tg_to_blkg(tg)) {
                struct throtl_grp *this_tg = blkg_to_tg(blkg);

                tg_update_has_rules(this_tg);
                /* ignore root/second level */
                if (!cgroup_subsys_on_dfl(io_cgrp_subsys) || !blkg->parent ||
                    !blkg->parent->parent)
                        continue;
        }
        rcu_read_unlock();

        /*
         * We're already holding queue_lock and know @tg is valid.  Let's
         * apply the new config directly.
         *
         * Restart the slices for both READ and WRITES. It might happen
         * that a group's limit are dropped suddenly and we don't want to
         * account recently dispatched IO with new low rate.
         */
        throtl_start_new_slice(tg, READ, false);
        throtl_start_new_slice(tg, WRITE, false);

        if (tg->flags & THROTL_TG_PENDING) {
                tg_update_disptime(tg);
                throtl_schedule_next_dispatch(sq->parent_sq, true);
        }
}

static int blk_throtl_init(struct gendisk *disk)
{
        struct request_queue *q = disk->queue;
        struct throtl_data *td;
        int ret;

        td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
        if (!td)
                return -ENOMEM;

        INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);
        throtl_service_queue_init(&td->service_queue);

        /*
         * Freeze queue before activating policy, to synchronize with IO path,
         * which is protected by 'q_usage_counter'.
         */
        blk_mq_freeze_queue(disk->queue);
        blk_mq_quiesce_queue(disk->queue);

        q->td = td;
        td->queue = q;

        /* activate policy */
        ret = blkcg_activate_policy(disk, &blkcg_policy_throtl);
        if (ret) {
                q->td = NULL;
                kfree(td);
                goto out;
        }

        if (blk_queue_nonrot(q))
                td->throtl_slice = DFL_THROTL_SLICE_SSD;
        else
                td->throtl_slice = DFL_THROTL_SLICE_HD;
        td->track_bio_latency = !queue_is_mq(q);
        if (!td->track_bio_latency)
                blk_stat_enable_accounting(q);

out:
        blk_mq_unquiesce_queue(disk->queue);
        blk_mq_unfreeze_queue(disk->queue);

        return ret;
}


static ssize_t tg_set_conf(struct kernfs_open_file *of,
                           char *buf, size_t nbytes, loff_t off, bool is_u64)
{
        struct blkcg *blkcg = css_to_blkcg(of_css(of));
        struct blkg_conf_ctx ctx;
        struct throtl_grp *tg;
        int ret;
        u64 v;

        blkg_conf_init(&ctx, buf);

        ret = blkg_conf_open_bdev(&ctx);
        if (ret)
                goto out_finish;

        if (!blk_throtl_activated(ctx.bdev->bd_queue)) {
                ret = blk_throtl_init(ctx.bdev->bd_disk);
                if (ret)
                        goto out_finish;
        }

        ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, &ctx);
        if (ret)
                goto out_finish;

        ret = -EINVAL;
        if (sscanf(ctx.body, "%llu", &v) != 1)
                goto out_finish;
        if (!v)
                v = U64_MAX;

        tg = blkg_to_tg(ctx.blkg);
        tg_update_carryover(tg);

        if (is_u64)
                *(u64 *)((void *)tg + of_cft(of)->private) = v;
        else
                *(unsigned int *)((void *)tg + of_cft(of)->private) = v;

        tg_conf_updated(tg, false);
        ret = 0;
out_finish:
        blkg_conf_exit(&ctx);
        return ret ?: nbytes;
}

static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
                               char *buf, size_t nbytes, loff_t off)
{
        return tg_set_conf(of, buf, nbytes, off, true);
}

static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
                                char *buf, size_t nbytes, loff_t off)
{
        return tg_set_conf(of, buf, nbytes, off, false);
}

static int tg_print_rwstat(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
                          blkg_prfill_rwstat, &blkcg_policy_throtl,
                          seq_cft(sf)->private, true);
        return 0;
}

static u64 tg_prfill_rwstat_recursive(struct seq_file *sf,
                                      struct blkg_policy_data *pd, int off)
{
        struct blkg_rwstat_sample sum;

        blkg_rwstat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_throtl, off,
                                  &sum);
        return __blkg_prfill_rwstat(sf, pd, &sum);
}

static int tg_print_rwstat_recursive(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
                          tg_prfill_rwstat_recursive, &blkcg_policy_throtl,
                          seq_cft(sf)->private, true);
        return 0;
}

static struct cftype throtl_legacy_files[] = {
        {
                .name = "throttle.read_bps_device",
                .private = offsetof(struct throtl_grp, bps[READ]),
                .seq_show = tg_print_conf_u64,
                .write = tg_set_conf_u64,
        },
        {
                .name = "throttle.write_bps_device",
                .private = offsetof(struct throtl_grp, bps[WRITE]),
                .seq_show = tg_print_conf_u64,
                .write = tg_set_conf_u64,
        },
        {
                .name = "throttle.read_iops_device",
                .private = offsetof(struct throtl_grp, iops[READ]),
                .seq_show = tg_print_conf_uint,
                .write = tg_set_conf_uint,
        },
        {
                .name = "throttle.write_iops_device",
                .private = offsetof(struct throtl_grp, iops[WRITE]),
                .seq_show = tg_print_conf_uint,
                .write = tg_set_conf_uint,
        },
        {
                .name = "throttle.io_service_bytes",
                .private = offsetof(struct throtl_grp, stat_bytes),
                .seq_show = tg_print_rwstat,
        },
        {
                .name = "throttle.io_service_bytes_recursive",
                .private = offsetof(struct throtl_grp, stat_bytes),
                .seq_show = tg_print_rwstat_recursive,
        },
        {
                .name = "throttle.io_serviced",
                .private = offsetof(struct throtl_grp, stat_ios),
                .seq_show = tg_print_rwstat,
        },
        {
                .name = "throttle.io_serviced_recursive",
                .private = offsetof(struct throtl_grp, stat_ios),
                .seq_show = tg_print_rwstat_recursive,
        },
        { }     /* terminate */
};

static u64 tg_prfill_limit(struct seq_file *sf, struct blkg_policy_data *pd,
                         int off)
{
        struct throtl_grp *tg = pd_to_tg(pd);
        const char *dname = blkg_dev_name(pd->blkg);
        u64 bps_dft;
        unsigned int iops_dft;

        if (!dname)
                return 0;

        bps_dft = U64_MAX;
        iops_dft = UINT_MAX;

        if (tg->bps[READ] == bps_dft &&
            tg->bps[WRITE] == bps_dft &&
            tg->iops[READ] == iops_dft &&
            tg->iops[WRITE] == iops_dft)
                return 0;

        seq_printf(sf, "%s", dname);
        if (tg->bps[READ] == U64_MAX)
                seq_printf(sf, " rbps=max");
        else
                seq_printf(sf, " rbps=%llu", tg->bps[READ]);

        if (tg->bps[WRITE] == U64_MAX)
                seq_printf(sf, " wbps=max");
        else
                seq_printf(sf, " wbps=%llu", tg->bps[WRITE]);

        if (tg->iops[READ] == UINT_MAX)
                seq_printf(sf, " riops=max");
        else
                seq_printf(sf, " riops=%u", tg->iops[READ]);

        if (tg->iops[WRITE] == UINT_MAX)
                seq_printf(sf, " wiops=max");
        else
                seq_printf(sf, " wiops=%u", tg->iops[WRITE]);

        seq_printf(sf, "\n");
        return 0;
}

static int tg_print_limit(struct seq_file *sf, void *v)
{
        blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_limit,
                          &blkcg_policy_throtl, seq_cft(sf)->private, false);
        return 0;
}

static ssize_t tg_set_limit(struct kernfs_open_file *of,
                          char *buf, size_t nbytes, loff_t off)
{
        struct blkcg *blkcg = css_to_blkcg(of_css(of));
        struct blkg_conf_ctx ctx;
        struct throtl_grp *tg;
        u64 v[4];
        int ret;

        blkg_conf_init(&ctx, buf);

        ret = blkg_conf_open_bdev(&ctx);
        if (ret)
                goto out_finish;

        if (!blk_throtl_activated(ctx.bdev->bd_queue)) {
                ret = blk_throtl_init(ctx.bdev->bd_disk);
                if (ret)
                        goto out_finish;
        }

        ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, &ctx);
        if (ret)
                goto out_finish;

        tg = blkg_to_tg(ctx.blkg);
        tg_update_carryover(tg);

        v[0] = tg->bps[READ];
        v[1] = tg->bps[WRITE];
        v[2] = tg->iops[READ];
        v[3] = tg->iops[WRITE];

        while (true) {
                char tok[27];   /* wiops=18446744073709551616 */
                char *p;
                u64 val = U64_MAX;
                int len;

                if (sscanf(ctx.body, "%26s%n", tok, &len) != 1)
                        break;
                if (tok[0] == '\0')
                        break;
                ctx.body += len;

                ret = -EINVAL;
                p = tok;
                strsep(&p, "=");
                if (!p || (sscanf(p, "%llu", &val) != 1 && strcmp(p, "max")))
                        goto out_finish;

                ret = -ERANGE;
                if (!val)
                        goto out_finish;

                ret = -EINVAL;
                if (!strcmp(tok, "rbps"))
                        v[0] = val;
                else if (!strcmp(tok, "wbps"))
                        v[1] = val;
                else if (!strcmp(tok, "riops"))
                        v[2] = min_t(u64, val, UINT_MAX);
                else if (!strcmp(tok, "wiops"))
                        v[3] = min_t(u64, val, UINT_MAX);
                else
                        goto out_finish;
        }

        tg->bps[READ] = v[0];
        tg->bps[WRITE] = v[1];
        tg->iops[READ] = v[2];
        tg->iops[WRITE] = v[3];

        tg_conf_updated(tg, false);
        ret = 0;
out_finish:
        blkg_conf_exit(&ctx);
        return ret ?: nbytes;
}

static struct cftype throtl_files[] = {
        {
                .name = "max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = tg_print_limit,
                .write = tg_set_limit,
        },
        { }     /* terminate */
};

static void throtl_shutdown_wq(struct request_queue *q)
{
        struct throtl_data *td = q->td;

        cancel_work_sync(&td->dispatch_work);
}

static void tg_flush_bios(struct throtl_grp *tg)
{
        struct throtl_service_queue *sq = &tg->service_queue;

        if (tg->flags & THROTL_TG_CANCELING)
                return;
        /*
         * Set the flag to make sure throtl_pending_timer_fn() won't
         * stop until all throttled bios are dispatched.
         */
        tg->flags |= THROTL_TG_CANCELING;

        /*
         * Do not dispatch cgroup without THROTL_TG_PENDING or cgroup
         * will be inserted to service queue without THROTL_TG_PENDING
         * set in tg_update_disptime below. Then IO dispatched from
         * child in tg_dispatch_one_bio will trigger double insertion
         * and corrupt the tree.
         */
        if (!(tg->flags & THROTL_TG_PENDING))
                return;

        /*
         * Update disptime after setting the above flag to make sure
         * throtl_select_dispatch() won't exit without dispatching.
         */
        tg_update_disptime(tg);

        throtl_schedule_pending_timer(sq, jiffies + 1);
}

static void throtl_pd_offline(struct blkg_policy_data *pd)
{
        tg_flush_bios(pd_to_tg(pd));
}

struct blkcg_policy blkcg_policy_throtl = {
        .dfl_cftypes            = throtl_files,
        .legacy_cftypes         = throtl_legacy_files,

        .pd_alloc_fn            = throtl_pd_alloc,
        .pd_init_fn             = throtl_pd_init,
        .pd_online_fn           = throtl_pd_online,
        .pd_offline_fn          = throtl_pd_offline,
        .pd_free_fn             = throtl_pd_free,
};

void blk_throtl_cancel_bios(struct gendisk *disk)
{
        struct request_queue *q = disk->queue;
        struct cgroup_subsys_state *pos_css;
        struct blkcg_gq *blkg;

        if (!blk_throtl_activated(q))
                return;

        spin_lock_irq(&q->queue_lock);
        /*
         * queue_lock is held, rcu lock is not needed here technically.
         * However, rcu lock is still held to emphasize that following
         * path need RCU protection and to prevent warning from lockdep.
         */
        rcu_read_lock();
        blkg_for_each_descendant_post(blkg, pos_css, q->root_blkg) {
                /*
                 * disk_release will call pd_offline_fn to cancel bios.
                 * However, disk_release can't be called if someone get
                 * the refcount of device and issued bios which are
                 * inflight after del_gendisk.
                 * Cancel bios here to ensure no bios are inflight after
                 * del_gendisk.
                 */
                tg_flush_bios(blkg_to_tg(blkg));
        }
        rcu_read_unlock();
        spin_unlock_irq(&q->queue_lock);
}

static bool tg_within_limit(struct throtl_grp *tg, struct bio *bio, bool rw)
{
        /* throtl is FIFO - if bios are already queued, should queue */
        if (tg->service_queue.nr_queued[rw])
                return false;

        return tg_may_dispatch(tg, bio, NULL);
}

static void tg_dispatch_in_debt(struct throtl_grp *tg, struct bio *bio, bool rw)
{
        if (!bio_flagged(bio, BIO_BPS_THROTTLED))
                tg->carryover_bytes[rw] -= throtl_bio_data_size(bio);
        tg->carryover_ios[rw]--;
}

bool __blk_throtl_bio(struct bio *bio)
{
        struct request_queue *q = bdev_get_queue(bio->bi_bdev);
        struct blkcg_gq *blkg = bio->bi_blkg;
        struct throtl_qnode *qn = NULL;
        struct throtl_grp *tg = blkg_to_tg(blkg);
        struct throtl_service_queue *sq;
        bool rw = bio_data_dir(bio);
        bool throttled = false;
        struct throtl_data *td = tg->td;

        rcu_read_lock();
        spin_lock_irq(&q->queue_lock);
        sq = &tg->service_queue;

        while (true) {
                if (tg_within_limit(tg, bio, rw)) {
                        /* within limits, let's charge and dispatch directly */
                        throtl_charge_bio(tg, bio);

                        /*
                         * We need to trim slice even when bios are not being
                         * queued otherwise it might happen that a bio is not
                         * queued for a long time and slice keeps on extending
                         * and trim is not called for a long time. Now if limits
                         * are reduced suddenly we take into account all the IO
                         * dispatched so far at new low rate and * newly queued
                         * IO gets a really long dispatch time.
                         *
                         * So keep on trimming slice even if bio is not queued.
                         */
                        throtl_trim_slice(tg, rw);
                } else if (bio_issue_as_root_blkg(bio)) {
                        /*
                         * IOs which may cause priority inversions are
                         * dispatched directly, even if they're over limit.
                         * Debts are handled by carryover_bytes/ios while
                         * calculating wait time.
                         */
                        tg_dispatch_in_debt(tg, bio, rw);
                } else {
                        /* if above limits, break to queue */
                        break;
                }

                /*
                 * @bio passed through this layer without being throttled.
                 * Climb up the ladder.  If we're already at the top, it
                 * can be executed directly.
                 */
                qn = &tg->qnode_on_parent[rw];
                sq = sq->parent_sq;
                tg = sq_to_tg(sq);
                if (!tg) {
                        bio_set_flag(bio, BIO_BPS_THROTTLED);
                        goto out_unlock;
                }
        }

        /* out-of-limit, queue to @tg */
        throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
                   rw == READ ? 'R' : 'W',
                   tg->bytes_disp[rw], bio->bi_iter.bi_size,
                   tg_bps_limit(tg, rw),
                   tg->io_disp[rw], tg_iops_limit(tg, rw),
                   sq->nr_queued[READ], sq->nr_queued[WRITE]);

        td->nr_queued[rw]++;
        throtl_add_bio_tg(bio, qn, tg);
        throttled = true;

        /*
         * Update @tg's dispatch time and force schedule dispatch if @tg
         * was empty before @bio.  The forced scheduling isn't likely to
         * cause undue delay as @bio is likely to be dispatched directly if
         * its @tg's disptime is not in the future.
         */
        if (tg->flags & THROTL_TG_WAS_EMPTY) {
                tg_update_disptime(tg);
                throtl_schedule_next_dispatch(tg->service_queue.parent_sq, true);
        }

out_unlock:
        spin_unlock_irq(&q->queue_lock);

        rcu_read_unlock();
        return throttled;
}

void blk_throtl_exit(struct gendisk *disk)
{
        struct request_queue *q = disk->queue;

        if (!blk_throtl_activated(q))
                return;

        del_timer_sync(&q->td->service_queue.pending_timer);
        throtl_shutdown_wq(q);
        blkcg_deactivate_policy(disk, &blkcg_policy_throtl);
        kfree(q->td);
}

static int __init throtl_init(void)
{
        kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
        if (!kthrotld_workqueue)
                panic("Failed to create kthrotld\n");

        return blkcg_policy_register(&blkcg_policy_throtl);
}

module_init(throtl_init);