/* * Interface for controlling IO bandwidth on a request queue * * Copyright (C) 2010 Vivek Goyal */ #include #include #include #include #include #include #include "blk.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 */ static struct blkcg_policy blkcg_policy_throtl; /* A workqueue to queue throttle related work */ static struct workqueue_struct *kthrotld_workqueue; /* * To implement hierarchical throttling, throtl_grps form a tree and bios * are dispatched upwards level by level until they reach the top and get * issued. When dispatching bios from the children and local group at each * level, if the bios are dispatched into a single bio_list, there's a risk * of a local or child group which can queue many bios at once filling up * the list starving others. * * To avoid such starvation, dispatched bios are queued separately * according to where they came from. When they are again dispatched to * the parent, they're popped in round-robin order so that no single source * hogs the dispatch window. * * throtl_qnode is used to keep the queued bios separated by their sources. * Bios are queued to throtl_qnode which in turn is queued to * throtl_service_queue and then dispatched in round-robin order. * * It's also used to track the reference counts on blkg's. A qnode always * belongs to a throtl_grp and gets queued on itself or the parent, so * incrementing the reference of the associated throtl_grp when a qnode is * queued and decrementing when dequeued is enough to keep the whole blkg * tree pinned while bios are in flight. */ struct throtl_qnode { struct list_head node; /* service_queue->queued[] */ struct bio_list bios; /* queued bios */ struct throtl_grp *tg; /* tg this qnode belongs to */ }; struct throtl_service_queue { struct throtl_service_queue *parent_sq; /* the parent service_queue */ /* * Bios queued directly to this service_queue or dispatched from * children throtl_grp's. */ struct list_head queued[2]; /* throtl_qnode [READ/WRITE] */ unsigned int nr_queued[2]; /* number of queued bios */ /* * RB tree of active children throtl_grp's, which are sorted by * their ->disptime. */ struct rb_root pending_tree; /* RB tree of active tgs */ struct rb_node *first_pending; /* first node in the tree */ unsigned int nr_pending; /* # queued in the tree */ unsigned long first_pending_disptime; /* disptime of the first tg */ struct timer_list pending_timer; /* fires on first_pending_disptime */ }; enum tg_state_flags { THROTL_TG_PENDING = 1 << 0, /* on parent's pending tree */ THROTL_TG_WAS_EMPTY = 1 << 1, /* bio_lists[] became non-empty */ }; #define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node) /* Per-cpu group stats */ struct tg_stats_cpu { /* total bytes transferred */ struct blkg_rwstat service_bytes; /* total IOs serviced, post merge */ struct blkg_rwstat serviced; }; struct throtl_grp { /* must be the first member */ struct blkg_policy_data pd; /* active throtl group service_queue member */ struct rb_node rb_node; /* throtl_data this group belongs to */ struct throtl_data *td; /* this group's service queue */ struct throtl_service_queue service_queue; /* * qnode_on_self is used when bios are directly queued to this * throtl_grp so that local bios compete fairly with bios * dispatched from children. qnode_on_parent is used when bios are * dispatched from this throtl_grp into its parent and will compete * with the sibling qnode_on_parents and the parent's * qnode_on_self. */ struct throtl_qnode qnode_on_self[2]; struct throtl_qnode qnode_on_parent[2]; /* * 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; unsigned int flags; /* are there any throtl rules between this group and td? */ bool has_rules[2]; /* bytes per second rate limits */ uint64_t bps[2]; /* IOPS limits */ unsigned int iops[2]; /* Number of bytes disptached in current slice */ uint64_t bytes_disp[2]; /* Number of bio's dispatched in current slice */ unsigned int io_disp[2]; /* When did we start a new slice */ unsigned long slice_start[2]; unsigned long slice_end[2]; /* Per cpu stats pointer */ struct tg_stats_cpu __percpu *stats_cpu; /* List of tgs waiting for per cpu stats memory to be allocated */ struct list_head stats_alloc_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]; /* * number of total undestroyed groups */ unsigned int nr_undestroyed_grps; /* Work for dispatching throttled bios */ struct work_struct dispatch_work; }; /* list and work item to allocate percpu group stats */ static DEFINE_SPINLOCK(tg_stats_alloc_lock); static LIST_HEAD(tg_stats_alloc_list); static void tg_stats_alloc_fn(struct work_struct *); static DECLARE_DELAYED_WORK(tg_stats_alloc_work, tg_stats_alloc_fn); static void throtl_pending_timer_fn(unsigned long arg); static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd) { return pd ? container_of(pd, struct throtl_grp, pd) : NULL; } static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg) { return pd_to_tg(blkg_to_pd(blkg, &blkcg_policy_throtl)); } static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg) { return pd_to_blkg(&tg->pd); } static inline struct throtl_grp *td_root_tg(struct throtl_data *td) { return blkg_to_tg(td->queue->root_blkg); } /** * 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 embeded 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); } /** * 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". * * TODO: this should be made a function and name formatting should happen * after testing whether blktrace is enabled. */ #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 ((__tg)) { \ char __pbuf[128]; \ \ blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf)); \ blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \ } else { \ blk_add_trace_msg(__td->queue, "throtl " fmt, ##args); \ } \ } while (0) static void tg_stats_init(struct tg_stats_cpu *tg_stats) { blkg_rwstat_init(&tg_stats->service_bytes); blkg_rwstat_init(&tg_stats->serviced); } /* * Worker for allocating per cpu stat for tgs. This is scheduled on the * system_wq once there are some groups on the alloc_list waiting for * allocation. */ static void tg_stats_alloc_fn(struct work_struct *work) { static struct tg_stats_cpu *stats_cpu; /* this fn is non-reentrant */ struct delayed_work *dwork = to_delayed_work(work); bool empty = false; alloc_stats: if (!stats_cpu) { int cpu; stats_cpu = alloc_percpu(struct tg_stats_cpu); if (!stats_cpu) { /* allocation failed, try again after some time */ schedule_delayed_work(dwork, msecs_to_jiffies(10)); return; } for_each_possible_cpu(cpu) tg_stats_init(per_cpu_ptr(stats_cpu, cpu)); } spin_lock_irq(&tg_stats_alloc_lock); if (!list_empty(&tg_stats_alloc_list)) { struct throtl_grp *tg = list_first_entry(&tg_stats_alloc_list, struct throtl_grp, stats_alloc_node); swap(tg->stats_cpu, stats_cpu); list_del_init(&tg->stats_alloc_node); } empty = list_empty(&tg_stats_alloc_list); spin_unlock_irq(&tg_stats_alloc_lock); if (!empty) goto alloc_stats; } 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 = list_first_entry(queued, struct throtl_qnode, node); struct bio *bio; if (list_empty(queued)) return NULL; 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 = list_first_entry(queued, struct throtl_qnode, node); struct bio *bio; if (list_empty(queued)) return NULL; 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, struct throtl_service_queue *parent_sq) { INIT_LIST_HEAD(&sq->queued[0]); INIT_LIST_HEAD(&sq->queued[1]); sq->pending_tree = RB_ROOT; sq->parent_sq = parent_sq; setup_timer(&sq->pending_timer, throtl_pending_timer_fn, (unsigned long)sq); } static void throtl_service_queue_exit(struct throtl_service_queue *sq) { del_timer_sync(&sq->pending_timer); } static void throtl_pd_init(struct blkcg_gq *blkg) { struct throtl_grp *tg = blkg_to_tg(blkg); struct throtl_data *td = blkg->q->td; struct throtl_service_queue *parent_sq; unsigned long flags; int rw; /* * 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 the root group, the whole system 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. */ parent_sq = &td->service_queue; if (cgroup_on_dfl(blkg->blkcg->css.cgroup) && blkg->parent) parent_sq = &blkg_to_tg(blkg->parent)->service_queue; throtl_service_queue_init(&tg->service_queue, parent_sq); 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->td = td; tg->bps[READ] = -1; tg->bps[WRITE] = -1; tg->iops[READ] = -1; tg->iops[WRITE] = -1; /* * Ugh... We need to perform per-cpu allocation for tg->stats_cpu * but percpu allocator can't be called from IO path. Queue tg on * tg_stats_alloc_list and allocate from work item. */ spin_lock_irqsave(&tg_stats_alloc_lock, flags); list_add(&tg->stats_alloc_node, &tg_stats_alloc_list); schedule_delayed_work(&tg_stats_alloc_work, 0); spin_unlock_irqrestore(&tg_stats_alloc_lock, flags); } /* * 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[rw] = (parent_tg && parent_tg->has_rules[rw]) || (tg->bps[rw] != -1 || tg->iops[rw] != -1); } static void throtl_pd_online(struct blkcg_gq *blkg) { /* * 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(blkg_to_tg(blkg)); } static void throtl_pd_exit(struct blkcg_gq *blkg) { struct throtl_grp *tg = blkg_to_tg(blkg); unsigned long flags; spin_lock_irqsave(&tg_stats_alloc_lock, flags); list_del_init(&tg->stats_alloc_node); spin_unlock_irqrestore(&tg_stats_alloc_lock, flags); free_percpu(tg->stats_cpu); throtl_service_queue_exit(&tg->service_queue); } static void throtl_pd_reset_stats(struct blkcg_gq *blkg) { struct throtl_grp *tg = blkg_to_tg(blkg); int cpu; if (tg->stats_cpu == NULL) return; for_each_possible_cpu(cpu) { struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu); blkg_rwstat_reset(&sc->service_bytes); blkg_rwstat_reset(&sc->serviced); } } static struct throtl_grp *throtl_lookup_tg(struct throtl_data *td, struct blkcg *blkcg) { /* * This is the common case when there are no blkcgs. Avoid lookup * in this case */ if (blkcg == &blkcg_root) return td_root_tg(td); return blkg_to_tg(blkg_lookup(blkcg, td->queue)); } static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td, struct blkcg *blkcg) { struct request_queue *q = td->queue; struct throtl_grp *tg = NULL; /* * This is the common case when there are no blkcgs. Avoid lookup * in this case */ if (blkcg == &blkcg_root) { tg = td_root_tg(td); } else { struct blkcg_gq *blkg; blkg = blkg_lookup_create(blkcg, q); /* if %NULL and @q is alive, fall back to root_tg */ if (!IS_ERR(blkg)) tg = blkg_to_tg(blkg); else if (!blk_queue_dying(q)) tg = td_root_tg(td); } return tg; } static struct throtl_grp * throtl_rb_first(struct throtl_service_queue *parent_sq) { /* Service tree is empty */ if (!parent_sq->nr_pending) return NULL; if (!parent_sq->first_pending) parent_sq->first_pending = rb_first(&parent_sq->pending_tree); if (parent_sq->first_pending) return rb_entry_tg(parent_sq->first_pending); 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_service_queue *parent_sq) { if (parent_sq->first_pending == n) parent_sq->first_pending = NULL; rb_erase_init(n, &parent_sq->pending_tree); --parent_sq->nr_pending; } 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_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) parent_sq->first_pending = &tg->rb_node; rb_link_node(&tg->rb_node, parent, node); rb_insert_color(&tg->rb_node, &parent_sq->pending_tree); } static void __throtl_enqueue_tg(struct throtl_grp *tg) { tg_service_queue_add(tg); tg->flags |= THROTL_TG_PENDING; tg->service_queue.parent_sq->nr_pending++; } static void throtl_enqueue_tg(struct throtl_grp *tg) { if (!(tg->flags & THROTL_TG_PENDING)) __throtl_enqueue_tg(tg); } static void __throtl_dequeue_tg(struct throtl_grp *tg) { throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq); tg->flags &= ~THROTL_TG_PENDING; } static void throtl_dequeue_tg(struct throtl_grp *tg) { if (tg->flags & THROTL_TG_PENDING) __throtl_dequeue_tg(tg); } /* Call with queue lock held */ static void throtl_schedule_pending_timer(struct throtl_service_queue *sq, unsigned long expires) { 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; /* * 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_eq(start, tg->slice_start[rw])) tg->slice_start[rw] = start; tg->slice_end[rw] = jiffies + 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) { tg->bytes_disp[rw] = 0; tg->io_disp[rw] = 0; tg->slice_start[rw] = jiffies; tg->slice_end[rw] = jiffies + throtl_slice; 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, throtl_slice); } static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw, unsigned long jiffy_end) { tg->slice_end[rw] = roundup(jiffy_end, throtl_slice); 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 1; } /* Trim the used slices and adjust slice start accordingly */ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw) { unsigned long nr_slices, time_elapsed, io_trim; u64 bytes_trim, tmp; 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 dispached * 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 + throtl_slice); time_elapsed = jiffies - tg->slice_start[rw]; nr_slices = time_elapsed / throtl_slice; if (!nr_slices) return; tmp = tg->bps[rw] * throtl_slice * nr_slices; do_div(tmp, HZ); bytes_trim = tmp; io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ; if (!bytes_trim && !io_trim) return; if (tg->bytes_disp[rw] >= bytes_trim) tg->bytes_disp[rw] -= bytes_trim; else tg->bytes_disp[rw] = 0; if (tg->io_disp[rw] >= io_trim) tg->io_disp[rw] -= io_trim; else tg->io_disp[rw] = 0; tg->slice_start[rw] += nr_slices * throtl_slice; throtl_log(&tg->service_queue, "[%c] trim slice nr=%lu bytes=%llu io=%lu start=%lu end=%lu jiffies=%lu", rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim, tg->slice_start[rw], tg->slice_end[rw], jiffies); } static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio, unsigned long *wait) { bool rw = bio_data_dir(bio); unsigned int io_allowed; unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; u64 tmp; 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); /* * jiffy_elapsed_rnd 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)tg->iops[rw] * jiffy_elapsed_rnd; do_div(tmp, HZ); if (tmp > UINT_MAX) io_allowed = UINT_MAX; else io_allowed = tmp; if (tg->io_disp[rw] + 1 <= io_allowed) { if (wait) *wait = 0; return true; } /* Calc approx time to dispatch */ jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1; if (jiffy_wait > jiffy_elapsed) jiffy_wait = jiffy_wait - jiffy_elapsed; else jiffy_wait = 1; if (wait) *wait = jiffy_wait; return 0; } static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio, unsigned long *wait) { bool rw = bio_data_dir(bio); u64 bytes_allowed, extra_bytes, tmp; unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; 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); tmp = tg->bps[rw] * jiffy_elapsed_rnd; do_div(tmp, HZ); bytes_allowed = tmp; if (tg->bytes_disp[rw] + bio->bi_iter.bi_size <= bytes_allowed) { if (wait) *wait = 0; return true; } /* Calc approx time to dispatch */ extra_bytes = tg->bytes_disp[rw] + bio->bi_iter.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; return 0; } /* * 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; /* * 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 (tg->bps[rw] == -1 && tg->iops[rw] == -1) { 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. */ if (throtl_slice_used(tg, rw)) throtl_start_new_slice(tg, rw); else { if (time_before(tg->slice_end[rw], jiffies + throtl_slice)) throtl_extend_slice(tg, rw, jiffies + throtl_slice); } if (tg_with_in_bps_limit(tg, bio, &bps_wait) && tg_with_in_iops_limit(tg, bio, &iops_wait)) { if (wait) *wait = 0; return 1; } 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 0; } static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes, int rw) { struct throtl_grp *tg = blkg_to_tg(blkg); struct tg_stats_cpu *stats_cpu; unsigned long flags; /* If per cpu stats are not allocated yet, don't do any accounting. */ if (tg->stats_cpu == NULL) return; /* * Disabling interrupts to provide mutual exclusion between two * writes on same cpu. It probably is not needed for 64bit. Not * optimizing that case yet. */ local_irq_save(flags); stats_cpu = this_cpu_ptr(tg->stats_cpu); blkg_rwstat_add(&stats_cpu->serviced, rw, 1); blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes); local_irq_restore(flags); } static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio) { bool rw = bio_data_dir(bio); /* Charge the bio to the group */ tg->bytes_disp[rw] += bio->bi_iter.bi_size; tg->io_disp[rw]++; /* * REQ_THROTTLED is used to prevent the same bio to be throttled * more than once as a throttled bio will go through blk-throtl the * second time when it eventually gets issued. Set it when a bio * is being charged to a tg. * * Dispatch stats aren't recursive and each @bio should only be * accounted by the @tg it was originally associated with. Let's * update the stats when setting REQ_THROTTLED for the first time * which is guaranteed to be for the @bio's original tg. */ if (!(bio->bi_rw & REQ_THROTTLED)) { bio->bi_rw |= REQ_THROTTLED; throtl_update_dispatch_stats(tg_to_blkg(tg), bio->bi_iter.bi_size, bio->bi_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 * cleaered 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; if ((bio = throtl_peek_queued(&sq->queued[READ]))) tg_may_dispatch(tg, bio, &read_wait); if ((bio = throtl_peek_queued(&sq->queued[WRITE]))) tg_may_dispatch(tg, bio, &write_wait); min_wait = min(read_wait, write_wait); disptime = jiffies + min_wait; /* Update dispatch time */ throtl_dequeue_tg(tg); tg->disptime = disptime; throtl_enqueue_tg(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 { 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, bio_data_dir(bio)); 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, bio_data_dir(bio)); 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 = throtl_rb_first(parent_sq); struct throtl_service_queue *sq = &tg->service_queue; if (!tg) break; if (time_before(jiffies, tg->disptime)) break; throtl_dequeue_tg(tg); nr_disp += throtl_dispatch_tg(tg); if (sq->nr_queued[0] || sq->nr_queued[1]) tg_update_disptime(tg); if (nr_disp >= throtl_quantum) break; } return nr_disp; } /** * throtl_pending_timer_fn - timer function for service_queue->pending_timer * @arg: 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(unsigned long arg) { struct throtl_service_queue *sq = (void *)arg; struct throtl_grp *tg = sq_to_tg(sq); struct throtl_data *td = sq_to_td(sq); struct request_queue *q = td->queue; struct throtl_service_queue *parent_sq; bool dispatched; int ret; spin_lock_irq(q->queue_lock); 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 issueing */ 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 bio's reach the bio_lists[] * of throtl_data->service_queue. Those bio's 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))) generic_make_request(bio); blk_finish_plug(&plug); } } static u64 tg_prfill_cpu_rwstat(struct seq_file *sf, struct blkg_policy_data *pd, int off) { struct throtl_grp *tg = pd_to_tg(pd); struct blkg_rwstat rwstat = { }, tmp; int i, cpu; if (tg->stats_cpu == NULL) return 0; for_each_possible_cpu(cpu) { struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu); tmp = blkg_rwstat_read((void *)sc + off); for (i = 0; i < BLKG_RWSTAT_NR; i++) rwstat.cnt[i] += tmp.cnt[i]; } return __blkg_prfill_rwstat(sf, pd, &rwstat); } static int tg_print_cpu_rwstat(struct seq_file *sf, void *v) { blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_cpu_rwstat, &blkcg_policy_throtl, seq_cft(sf)->private, true); return 0; } 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 == -1) 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 == -1) 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 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; struct throtl_service_queue *sq; struct blkcg_gq *blkg; struct cgroup_subsys_state *pos_css; int ret; ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx); if (ret) return ret; tg = blkg_to_tg(ctx.blkg); sq = &tg->service_queue; if (!ctx.v) ctx.v = -1; if (is_u64) *(u64 *)((void *)tg + of_cft(of)->private) = ctx.v; else *(unsigned int *)((void *)tg + of_cft(of)->private) = ctx.v; throtl_log(&tg->service_queue, "limit change rbps=%llu wbps=%llu riops=%u wiops=%u", tg->bps[READ], tg->bps[WRITE], tg->iops[READ], tg->iops[WRITE]); /* * 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, ctx.blkg) tg_update_has_rules(blkg_to_tg(blkg)); /* * 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, 0); throtl_start_new_slice(tg, 1); if (tg->flags & THROTL_TG_PENDING) { tg_update_disptime(tg); throtl_schedule_next_dispatch(sq->parent_sq, true); } blkg_conf_finish(&ctx); return 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 struct cftype throtl_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 tg_stats_cpu, service_bytes), .seq_show = tg_print_cpu_rwstat, }, { .name = "throttle.io_serviced", .private = offsetof(struct tg_stats_cpu, serviced), .seq_show = tg_print_cpu_rwstat, }, { } /* terminate */ }; static void throtl_shutdown_wq(struct request_queue *q) { struct throtl_data *td = q->td; cancel_work_sync(&td->dispatch_work); } static struct blkcg_policy blkcg_policy_throtl = { .pd_size = sizeof(struct throtl_grp), .cftypes = throtl_files, .pd_init_fn = throtl_pd_init, .pd_online_fn = throtl_pd_online, .pd_exit_fn = throtl_pd_exit, .pd_reset_stats_fn = throtl_pd_reset_stats, }; bool blk_throtl_bio(struct request_queue *q, struct bio *bio) { struct throtl_data *td = q->td; struct throtl_qnode *qn = NULL; struct throtl_grp *tg; struct throtl_service_queue *sq; bool rw = bio_data_dir(bio); struct blkcg *blkcg; bool throttled = false; /* see throtl_charge_bio() */ if (bio->bi_rw & REQ_THROTTLED) goto out; /* * A throtl_grp pointer retrieved under rcu can be used to access * basic fields like stats and io rates. If a group has no rules, * just update the dispatch stats in lockless manner and return. */ rcu_read_lock(); blkcg = bio_blkcg(bio); tg = throtl_lookup_tg(td, blkcg); if (tg) { if (!tg->has_rules[rw]) { throtl_update_dispatch_stats(tg_to_blkg(tg), bio->bi_iter.bi_size, bio->bi_rw); goto out_unlock_rcu; } } /* * Either group has not been allocated yet or it is not an unlimited * IO group */ spin_lock_irq(q->queue_lock); tg = throtl_lookup_create_tg(td, blkcg); if (unlikely(!tg)) goto out_unlock; sq = &tg->service_queue; while (true) { /* throtl is FIFO - if bios are already queued, should queue */ if (sq->nr_queued[rw]) break; /* if above limits, break to queue */ if (!tg_may_dispatch(tg, bio, NULL)) break; /* 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); /* * @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) 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[rw], tg->io_disp[rw], tg->iops[rw], sq->nr_queued[READ], sq->nr_queued[WRITE]); bio_associate_current(bio); tg->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); out_unlock_rcu: rcu_read_unlock(); out: /* * As multiple blk-throtls may stack in the same issue path, we * don't want bios to leave with the flag set. Clear the flag if * being issued. */ if (!throttled) bio->bi_rw &= ~REQ_THROTTLED; return throttled; } /* * Dispatch all bios from all children tg's queued on @parent_sq. On * return, @parent_sq is guaranteed to not have any active children tg's * and all bios from previously active tg's are on @parent_sq->bio_lists[]. */ static void tg_drain_bios(struct throtl_service_queue *parent_sq) { struct throtl_grp *tg; while ((tg = throtl_rb_first(parent_sq))) { struct throtl_service_queue *sq = &tg->service_queue; struct bio *bio; throtl_dequeue_tg(tg); while ((bio = throtl_peek_queued(&sq->queued[READ]))) tg_dispatch_one_bio(tg, bio_data_dir(bio)); while ((bio = throtl_peek_queued(&sq->queued[WRITE]))) tg_dispatch_one_bio(tg, bio_data_dir(bio)); } } /** * blk_throtl_drain - drain throttled bios * @q: request_queue to drain throttled bios for * * Dispatch all currently throttled bios on @q through ->make_request_fn(). */ void blk_throtl_drain(struct request_queue *q) __releases(q->queue_lock) __acquires(q->queue_lock) { struct throtl_data *td = q->td; struct blkcg_gq *blkg; struct cgroup_subsys_state *pos_css; struct bio *bio; int rw; queue_lockdep_assert_held(q); rcu_read_lock(); /* * Drain each tg while doing post-order walk on the blkg tree, so * that all bios are propagated to td->service_queue. It'd be * better to walk service_queue tree directly but blkg walk is * easier. */ blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) tg_drain_bios(&blkg_to_tg(blkg)->service_queue); /* finally, transfer bios from top-level tg's into the td */ tg_drain_bios(&td->service_queue); rcu_read_unlock(); spin_unlock_irq(q->queue_lock); /* all bios now should be in td->service_queue, issue them */ for (rw = READ; rw <= WRITE; rw++) while ((bio = throtl_pop_queued(&td->service_queue.queued[rw], NULL))) generic_make_request(bio); spin_lock_irq(q->queue_lock); } int blk_throtl_init(struct request_queue *q) { 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, NULL); q->td = td; td->queue = q; /* activate policy */ ret = blkcg_activate_policy(q, &blkcg_policy_throtl); if (ret) kfree(td); return ret; } void blk_throtl_exit(struct request_queue *q) { BUG_ON(!q->td); throtl_shutdown_wq(q); blkcg_deactivate_policy(q, &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);