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 // SPDX-License-Identifier: GPL-2.0
 /*
  * buffered writeback throttling. loosely based on CoDel. We can't drop
  * packets for IO scheduling, so the logic is something like this:
  *
  * - Monitor latencies in a defined window of time.
  * - If the minimum latency in the above window exceeds some target, increment
  *   scaling step and scale down queue depth by a factor of 2x. The monitoring
  *   window is then shrunk to 100 / sqrt(scaling step + 1).
  * - For any window where we don't have solid data on what the latencies
  *   look like, retain status quo.
  * - If latencies look good, decrement scaling step.
  * - If we're only doing writes, allow the scaling step to go negative. This
  *   will temporarily boost write performance, snapping back to a stable
  *   scaling step of 0 if reads show up or the heavy writers finish. Unlike
  *   positive scaling steps where we shrink the monitoring window, a negative
  *   scaling step retains the default step==0 window size.
  *
  * Copyright (C) 2016 Jens Axboe
  *
  */
 #include <linux/kernel.h>
 #include <linux/blk_types.h>
 #include <linux/slab.h>
 #include <linux/backing-dev.h>
 #include <linux/swap.h>
 
 #include "blk-wbt.h"
 #include "blk-rq-qos.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/wbt.h>
 
 static inline void wbt_clear_state(struct request *rq)
 {
     rq->wbt_flags = 0;
 }
 
 static inline enum wbt_flags wbt_flags(struct request *rq)
 {
     return rq->wbt_flags;
 }
 
 static inline bool wbt_is_tracked(struct request *rq)
 {
     return rq->wbt_flags & WBT_TRACKED;
 }
 
 static inline bool wbt_is_read(struct request *rq)
 {
     return rq->wbt_flags & WBT_READ;
 }
 
 enum {
     /*
      * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
      * from here depending on device stats
      */
     RWB_DEF_DEPTH   = 16,
 
     /*
      * 100msec window
      */
     RWB_WINDOW_NSEC     = 100 * 1000 * 1000ULL,
 
     /*
      * Disregard stats, if we don't meet this minimum
      */
     RWB_MIN_WRITE_SAMPLES   = 3,
 
     /*
      * If we have this number of consecutive windows with not enough
      * information to scale up or down, scale up.
      */
     RWB_UNKNOWN_BUMP    = 5,
 };
 
 static inline bool rwb_enabled(struct rq_wb *rwb)
 {
     return rwb && rwb->enable_state != WBT_STATE_OFF_DEFAULT &&
               rwb->wb_normal != 0;
 }
 
 static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
 {
     if (rwb_enabled(rwb)) {
         const unsigned long cur = jiffies;
 
         if (cur != *var)
             *var = cur;
     }
 }
 
 /*
  * If a task was rate throttled in balance_dirty_pages() within the last
  * second or so, use that to indicate a higher cleaning rate.
  */
 static bool wb_recent_wait(struct rq_wb *rwb)
 {
     struct bdi_writeback *wb = &rwb->rqos.q->disk->bdi->wb;
 
     return time_before(jiffies, wb->dirty_sleep + HZ);
 }
 
 static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,
                       enum wbt_flags wb_acct)
 {
     if (wb_acct & WBT_KSWAPD)
         return &rwb->rq_wait[WBT_RWQ_KSWAPD];
     else if (wb_acct & WBT_DISCARD)
         return &rwb->rq_wait[WBT_RWQ_DISCARD];
 
     return &rwb->rq_wait[WBT_RWQ_BG];
 }
 
 static void rwb_wake_all(struct rq_wb *rwb)
 {
     int i;
 
     for (i = 0; i < WBT_NUM_RWQ; i++) {
         struct rq_wait *rqw = &rwb->rq_wait[i];
 
         if (wq_has_sleeper(&rqw->wait))
             wake_up_all(&rqw->wait);
     }
 }
 
 static void wbt_rqw_done(struct rq_wb *rwb, struct rq_wait *rqw,
              enum wbt_flags wb_acct)
 {
     int inflight, limit;
 
     inflight = atomic_dec_return(&rqw->inflight);
 
     /*
      * wbt got disabled with IO in flight. Wake up any potential
      * waiters, we don't have to do more than that.
      */
     if (unlikely(!rwb_enabled(rwb))) {
         rwb_wake_all(rwb);
         return;
     }
 
     /*
      * For discards, our limit is always the background. For writes, if
      * the device does write back caching, drop further down before we
      * wake people up.
      */
     if (wb_acct & WBT_DISCARD)
         limit = rwb->wb_background;
     else if (rwb->wc && !wb_recent_wait(rwb))
         limit = 0;
     else
         limit = rwb->wb_normal;
 
     /*
      * Don't wake anyone up if we are above the normal limit.
      */
     if (inflight && inflight >= limit)
         return;
 
     if (wq_has_sleeper(&rqw->wait)) {
         int diff = limit - inflight;
 
         if (!inflight || diff >= rwb->wb_background / 2)
             wake_up_all(&rqw->wait);
     }
 }
 
 static void __wbt_done(struct rq_qos *rqos, enum wbt_flags wb_acct)
 {
     struct rq_wb *rwb = RQWB(rqos);
     struct rq_wait *rqw;
 
     if (!(wb_acct & WBT_TRACKED))
         return;
 
     rqw = get_rq_wait(rwb, wb_acct);
     wbt_rqw_done(rwb, rqw, wb_acct);
 }
 
 /*
  * Called on completion of a request. Note that it's also called when
  * a request is merged, when the request gets freed.
  */
 static void wbt_done(struct rq_qos *rqos, struct request *rq)
 {
     struct rq_wb *rwb = RQWB(rqos);
 
     if (!wbt_is_tracked(rq)) {
         if (rwb->sync_cookie == rq) {
             rwb->sync_issue = 0;
             rwb->sync_cookie = NULL;
         }
 
         if (wbt_is_read(rq))
             wb_timestamp(rwb, &rwb->last_comp);
     } else {
         WARN_ON_ONCE(rq == rwb->sync_cookie);
         __wbt_done(rqos, wbt_flags(rq));
     }
     wbt_clear_state(rq);
 }
 
 static inline bool stat_sample_valid(struct blk_rq_stat *stat)
 {
     /*
      * We need at least one read sample, and a minimum of
      * RWB_MIN_WRITE_SAMPLES. We require some write samples to know
      * that it's writes impacting us, and not just some sole read on
      * a device that is in a lower power state.
      */
     return (stat[READ].nr_samples >= 1 &&
         stat[WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES);
 }
 
 static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
 {
     u64 now, issue = READ_ONCE(rwb->sync_issue);
 
     if (!issue || !rwb->sync_cookie)
         return 0;
 
     now = ktime_to_ns(ktime_get());
     return now - issue;
 }
 
 enum {
     LAT_OK = 1,
     LAT_UNKNOWN,
     LAT_UNKNOWN_WRITES,
     LAT_EXCEEDED,
 };
 
 static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
 {
     struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;
     struct rq_depth *rqd = &rwb->rq_depth;
     u64 thislat;
 
     /*
      * If our stored sync issue exceeds the window size, or it
      * exceeds our min target AND we haven't logged any entries,
      * flag the latency as exceeded. wbt works off completion latencies,
      * but for a flooded device, a single sync IO can take a long time
      * to complete after being issued. If this time exceeds our
      * monitoring window AND we didn't see any other completions in that
      * window, then count that sync IO as a violation of the latency.
      */
     thislat = rwb_sync_issue_lat(rwb);
     if (thislat > rwb->cur_win_nsec ||
         (thislat > rwb->min_lat_nsec && !stat[READ].nr_samples)) {
         trace_wbt_lat(bdi, thislat);
         return LAT_EXCEEDED;
     }
 
     /*
      * No read/write mix, if stat isn't valid
      */
     if (!stat_sample_valid(stat)) {
         /*
          * If we had writes in this stat window and the window is
          * current, we're only doing writes. If a task recently
          * waited or still has writes in flights, consider us doing
          * just writes as well.
          */
         if (stat[WRITE].nr_samples || wb_recent_wait(rwb) ||
             wbt_inflight(rwb))
             return LAT_UNKNOWN_WRITES;
         return LAT_UNKNOWN;
     }
 
     /*
      * If the 'min' latency exceeds our target, step down.
      */
     if (stat[READ].min > rwb->min_lat_nsec) {
         trace_wbt_lat(bdi, stat[READ].min);
         trace_wbt_stat(bdi, stat);
         return LAT_EXCEEDED;
     }
 
     if (rqd->scale_step)
         trace_wbt_stat(bdi, stat);
 
     return LAT_OK;
 }
 
 static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
 {
     struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;
     struct rq_depth *rqd = &rwb->rq_depth;
 
     trace_wbt_step(bdi, msg, rqd->scale_step, rwb->cur_win_nsec,
             rwb->wb_background, rwb->wb_normal, rqd->max_depth);
 }
 
 static void calc_wb_limits(struct rq_wb *rwb)
 {
     if (rwb->min_lat_nsec == 0) {
         rwb->wb_normal = rwb->wb_background = 0;
     } else if (rwb->rq_depth.max_depth <= 2) {
         rwb->wb_normal = rwb->rq_depth.max_depth;
         rwb->wb_background = 1;
     } else {
         rwb->wb_normal = (rwb->rq_depth.max_depth + 1) / 2;
         rwb->wb_background = (rwb->rq_depth.max_depth + 3) / 4;
     }
 }
 
 static void scale_up(struct rq_wb *rwb)
 {
     if (!rq_depth_scale_up(&rwb->rq_depth))
         return;
     calc_wb_limits(rwb);
     rwb->unknown_cnt = 0;
     rwb_wake_all(rwb);
     rwb_trace_step(rwb, tracepoint_string("scale up"));
 }
 
 static void scale_down(struct rq_wb *rwb, bool hard_throttle)
 {
     if (!rq_depth_scale_down(&rwb->rq_depth, hard_throttle))
         return;
     calc_wb_limits(rwb);
     rwb->unknown_cnt = 0;
     rwb_trace_step(rwb, tracepoint_string("scale down"));
 }
 
 static void rwb_arm_timer(struct rq_wb *rwb)
 {
     struct rq_depth *rqd = &rwb->rq_depth;
 
     if (rqd->scale_step > 0) {
         /*
          * We should speed this up, using some variant of a fast
          * integer inverse square root calculation. Since we only do
          * this for every window expiration, it's not a huge deal,
          * though.
          */
         rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
                     int_sqrt((rqd->scale_step + 1) << 8));
     } else {
         /*
          * For step < 0, we don't want to increase/decrease the
          * window size.
          */
         rwb->cur_win_nsec = rwb->win_nsec;
     }
 
     blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec);
 }
 
 static void wb_timer_fn(struct blk_stat_callback *cb)
 {
     struct rq_wb *rwb = cb->data;
     struct rq_depth *rqd = &rwb->rq_depth;
     unsigned int inflight = wbt_inflight(rwb);
     int status;
 
     if (!rwb->rqos.q->disk)
         return;
 
     status = latency_exceeded(rwb, cb->stat);
 
     trace_wbt_timer(rwb->rqos.q->disk->bdi, status, rqd->scale_step,
             inflight);
 
     /*
      * If we exceeded the latency target, step down. If we did not,
      * step one level up. If we don't know enough to say either exceeded
      * or ok, then don't do anything.
      */
     switch (status) {
     case LAT_EXCEEDED:
         scale_down(rwb, true);
         break;
     case LAT_OK:
         scale_up(rwb);
         break;
     case LAT_UNKNOWN_WRITES:
         /*
          * We started a the center step, but don't have a valid
          * read/write sample, but we do have writes going on.
          * Allow step to go negative, to increase write perf.
          */
         scale_up(rwb);
         break;
     case LAT_UNKNOWN:
         if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
             break;
         /*
          * We get here when previously scaled reduced depth, and we
          * currently don't have a valid read/write sample. For that
          * case, slowly return to center state (step == 0).
          */
         if (rqd->scale_step > 0)
             scale_up(rwb);
         else if (rqd->scale_step < 0)
             scale_down(rwb, false);
         break;
     default:
         break;
     }
 
     /*
      * Re-arm timer, if we have IO in flight
      */
     if (rqd->scale_step || inflight)
         rwb_arm_timer(rwb);
 }
 
 static void wbt_update_limits(struct rq_wb *rwb)
 {
     struct rq_depth *rqd = &rwb->rq_depth;
 
     rqd->scale_step = 0;
     rqd->scaled_max = false;
 
     rq_depth_calc_max_depth(rqd);
     calc_wb_limits(rwb);
 
     rwb_wake_all(rwb);
 }
 
 u64 wbt_get_min_lat(struct request_queue *q)
 {
     struct rq_qos *rqos = wbt_rq_qos(q);
     if (!rqos)
         return 0;
     return RQWB(rqos)->min_lat_nsec;
 }
 
 void wbt_set_min_lat(struct request_queue *q, u64 val)
 {
     struct rq_qos *rqos = wbt_rq_qos(q);
     if (!rqos)
         return;
     RQWB(rqos)->min_lat_nsec = val;
     RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL;
     wbt_update_limits(RQWB(rqos));
 }
 
 
 static bool close_io(struct rq_wb *rwb)
 {
     const unsigned long now = jiffies;
 
     return time_before(now, rwb->last_issue + HZ / 10) ||
         time_before(now, rwb->last_comp + HZ / 10);
 }
 
 #define REQ_HIPRIO  (REQ_SYNC | REQ_META | REQ_PRIO)
 
 static inline unsigned int get_limit(struct rq_wb *rwb, blk_opf_t opf)
 {
     unsigned int limit;
 
     /*
      * If we got disabled, just return UINT_MAX. This ensures that
      * we'll properly inc a new IO, and dec+wakeup at the end.
      */
     if (!rwb_enabled(rwb))
         return UINT_MAX;
 
     if ((opf & REQ_OP_MASK) == REQ_OP_DISCARD)
         return rwb->wb_background;
 
     /*
      * At this point we know it's a buffered write. If this is
      * kswapd trying to free memory, or REQ_SYNC is set, then
      * it's WB_SYNC_ALL writeback, and we'll use the max limit for
      * that. If the write is marked as a background write, then use
      * the idle limit, or go to normal if we haven't had competing
      * IO for a bit.
      */
     if ((opf & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
         limit = rwb->rq_depth.max_depth;
     else if ((opf & REQ_BACKGROUND) || close_io(rwb)) {
         /*
          * If less than 100ms since we completed unrelated IO,
          * limit us to half the depth for background writeback.
          */
         limit = rwb->wb_background;
     } else
         limit = rwb->wb_normal;
 
     return limit;
 }
 
 struct wbt_wait_data {
     struct rq_wb *rwb;
     enum wbt_flags wb_acct;
     blk_opf_t opf;
 };
 
 static bool wbt_inflight_cb(struct rq_wait *rqw, void *private_data)
 {
     struct wbt_wait_data *data = private_data;
     return rq_wait_inc_below(rqw, get_limit(data->rwb, data->opf));
 }
 
 static void wbt_cleanup_cb(struct rq_wait *rqw, void *private_data)
 {
     struct wbt_wait_data *data = private_data;
     wbt_rqw_done(data->rwb, rqw, data->wb_acct);
 }
 
 /*
  * Block if we will exceed our limit, or if we are currently waiting for
  * the timer to kick off queuing again.
  */
 static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
                blk_opf_t opf)
 {
     struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);
     struct wbt_wait_data data = {
         .rwb = rwb,
         .wb_acct = wb_acct,
         .opf = opf,
     };
 
     rq_qos_wait(rqw, &data, wbt_inflight_cb, wbt_cleanup_cb);
 }
 
 static inline bool wbt_should_throttle(struct bio *bio)
 {
     switch (bio_op(bio)) {
     case REQ_OP_WRITE:
         /*
          * Don't throttle WRITE_ODIRECT
          */
         if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==
             (REQ_SYNC | REQ_IDLE))
             return false;
         fallthrough;
     case REQ_OP_DISCARD:
         return true;
     default:
         return false;
     }
 }
 
 static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio)
 {
     enum wbt_flags flags = 0;
 
     if (!rwb_enabled(rwb))
         return 0;
 
     if (bio_op(bio) == REQ_OP_READ) {
         flags = WBT_READ;
     } else if (wbt_should_throttle(bio)) {
         if (current_is_kswapd())
             flags |= WBT_KSWAPD;
         if (bio_op(bio) == REQ_OP_DISCARD)
             flags |= WBT_DISCARD;
         flags |= WBT_TRACKED;
     }
     return flags;
 }
 
 static void wbt_cleanup(struct rq_qos *rqos, struct bio *bio)
 {
     struct rq_wb *rwb = RQWB(rqos);
     enum wbt_flags flags = bio_to_wbt_flags(rwb, bio);
     __wbt_done(rqos, flags);
 }
 
 /*
  * May sleep, if we have exceeded the writeback limits. Caller can pass
  * in an irq held spinlock, if it holds one when calling this function.
  * If we do sleep, we'll release and re-grab it.
  */
 static void wbt_wait(struct rq_qos *rqos, struct bio *bio)
 {
     struct rq_wb *rwb = RQWB(rqos);
     enum wbt_flags flags;
 
     flags = bio_to_wbt_flags(rwb, bio);
     if (!(flags & WBT_TRACKED)) {
         if (flags & WBT_READ)
             wb_timestamp(rwb, &rwb->last_issue);
         return;
     }
 
     __wbt_wait(rwb, flags, bio->bi_opf);
 
     if (!blk_stat_is_active(rwb->cb))
         rwb_arm_timer(rwb);
 }
 
 static void wbt_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
 {
     struct rq_wb *rwb = RQWB(rqos);
     rq->wbt_flags |= bio_to_wbt_flags(rwb, bio);
 }
 
 static void wbt_issue(struct rq_qos *rqos, struct request *rq)
 {
     struct rq_wb *rwb = RQWB(rqos);
 
     if (!rwb_enabled(rwb))
         return;
 
     /*
      * Track sync issue, in case it takes a long time to complete. Allows us
      * to react quicker, if a sync IO takes a long time to complete. Note
      * that this is just a hint. The request can go away when it completes,
      * so it's important we never dereference it. We only use the address to
      * compare with, which is why we store the sync_issue time locally.
      */
     if (wbt_is_read(rq) && !rwb->sync_issue) {
         rwb->sync_cookie = rq;
         rwb->sync_issue = rq->io_start_time_ns;
     }
 }
 
 static void wbt_requeue(struct rq_qos *rqos, struct request *rq)
 {
     struct rq_wb *rwb = RQWB(rqos);
     if (!rwb_enabled(rwb))
         return;
     if (rq == rwb->sync_cookie) {
         rwb->sync_issue = 0;
         rwb->sync_cookie = NULL;
     }
 }
 
 void wbt_set_write_cache(struct request_queue *q, bool write_cache_on)
 {
     struct rq_qos *rqos = wbt_rq_qos(q);
     if (rqos)
         RQWB(rqos)->wc = write_cache_on;
 }
 
 /*
  * Enable wbt if defaults are configured that way
  */
 void wbt_enable_default(struct request_queue *q)
 {
     struct rq_qos *rqos = wbt_rq_qos(q);
 
     /* Throttling already enabled? */
     if (rqos) {
         if (RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
             RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;
         return;
     }
 
     /* Queue not registered? Maybe shutting down... */
     if (!blk_queue_registered(q))
         return;
 
     if (queue_is_mq(q) && IS_ENABLED(CONFIG_BLK_WBT_MQ))
         wbt_init(q);
 }
 EXPORT_SYMBOL_GPL(wbt_enable_default);
 
 u64 wbt_default_latency_nsec(struct request_queue *q)
 {
     /*
      * We default to 2msec for non-rotational storage, and 75msec
      * for rotational storage.
      */
     if (blk_queue_nonrot(q))
         return 2000000ULL;
     else
         return 75000000ULL;
 }
 
 static int wbt_data_dir(const struct request *rq)
 {
     const enum req_op op = req_op(rq);
 
     if (op == REQ_OP_READ)
         return READ;
     else if (op_is_write(op))
         return WRITE;
 
     /* don't account */
     return -1;
 }
 
 static void wbt_queue_depth_changed(struct rq_qos *rqos)
 {
     RQWB(rqos)->rq_depth.queue_depth = blk_queue_depth(rqos->q);
     wbt_update_limits(RQWB(rqos));
 }
 
 static void wbt_exit(struct rq_qos *rqos)
 {
     struct rq_wb *rwb = RQWB(rqos);
     struct request_queue *q = rqos->q;
 
     blk_stat_remove_callback(q, rwb->cb);
     blk_stat_free_callback(rwb->cb);
     kfree(rwb);
 }
 
 /*
  * Disable wbt, if enabled by default.
  */
 void wbt_disable_default(struct request_queue *q)
 {
     struct rq_qos *rqos = wbt_rq_qos(q);
     struct rq_wb *rwb;
     if (!rqos)
         return;
     rwb = RQWB(rqos);
     if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {
         blk_stat_deactivate(rwb->cb);
         rwb->enable_state = WBT_STATE_OFF_DEFAULT;
     }
 }
 EXPORT_SYMBOL_GPL(wbt_disable_default);
 
 #ifdef CONFIG_BLK_DEBUG_FS
 static int wbt_curr_win_nsec_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
     struct rq_wb *rwb = RQWB(rqos);
 
     seq_printf(m, "%llu\n", rwb->cur_win_nsec);
     return 0;
 }
 
 static int wbt_enabled_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
     struct rq_wb *rwb = RQWB(rqos);
 
     seq_printf(m, "%d\n", rwb->enable_state);
     return 0;
 }
 
 static int wbt_id_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
 
     seq_printf(m, "%u\n", rqos->id);
     return 0;
 }
 
 static int wbt_inflight_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
     struct rq_wb *rwb = RQWB(rqos);
     int i;
 
     for (i = 0; i < WBT_NUM_RWQ; i++)
         seq_printf(m, "%d: inflight %d\n", i,
                atomic_read(&rwb->rq_wait[i].inflight));
     return 0;
 }
 
 static int wbt_min_lat_nsec_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
     struct rq_wb *rwb = RQWB(rqos);
 
     seq_printf(m, "%lu\n", rwb->min_lat_nsec);
     return 0;
 }
 
 static int wbt_unknown_cnt_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
     struct rq_wb *rwb = RQWB(rqos);
 
     seq_printf(m, "%u\n", rwb->unknown_cnt);
     return 0;
 }
 
 static int wbt_normal_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
     struct rq_wb *rwb = RQWB(rqos);
 
     seq_printf(m, "%u\n", rwb->wb_normal);
     return 0;
 }
 
 static int wbt_background_show(void *data, struct seq_file *m)
 {
     struct rq_qos *rqos = data;
     struct rq_wb *rwb = RQWB(rqos);
 
     seq_printf(m, "%u\n", rwb->wb_background);
     return 0;
 }
 
 static const struct blk_mq_debugfs_attr wbt_debugfs_attrs[] = {
     {"curr_win_nsec", 0400, wbt_curr_win_nsec_show},
     {"enabled", 0400, wbt_enabled_show},
     {"id", 0400, wbt_id_show},
     {"inflight", 0400, wbt_inflight_show},
     {"min_lat_nsec", 0400, wbt_min_lat_nsec_show},
     {"unknown_cnt", 0400, wbt_unknown_cnt_show},
     {"wb_normal", 0400, wbt_normal_show},
     {"wb_background", 0400, wbt_background_show},
     {},
 };
 #endif
 
 static struct rq_qos_ops wbt_rqos_ops = {
     .throttle = wbt_wait,
     .issue = wbt_issue,
     .track = wbt_track,
     .requeue = wbt_requeue,
     .done = wbt_done,
     .cleanup = wbt_cleanup,
     .queue_depth_changed = wbt_queue_depth_changed,
     .exit = wbt_exit,
 #ifdef CONFIG_BLK_DEBUG_FS
     .debugfs_attrs = wbt_debugfs_attrs,
 #endif
 };
 
 int wbt_init(struct request_queue *q)
 {
     struct rq_wb *rwb;
     int i;
     int ret;
 
     rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
     if (!rwb)
         return -ENOMEM;
 
     rwb->cb = blk_stat_alloc_callback(wb_timer_fn, wbt_data_dir, 2, rwb);
     if (!rwb->cb) {
         kfree(rwb);
         return -ENOMEM;
     }
 
     for (i = 0; i < WBT_NUM_RWQ; i++)
         rq_wait_init(&rwb->rq_wait[i]);
 
     rwb->rqos.id = RQ_QOS_WBT;
     rwb->rqos.ops = &wbt_rqos_ops;
     rwb->rqos.q = q;
     rwb->last_comp = rwb->last_issue = jiffies;
     rwb->win_nsec = RWB_WINDOW_NSEC;
     rwb->enable_state = WBT_STATE_ON_DEFAULT;
     rwb->wc = 1;
     rwb->rq_depth.default_depth = RWB_DEF_DEPTH;
 
     /*
      * Assign rwb and add the stats callback.
      */
     ret = rq_qos_add(q, &rwb->rqos);
     if (ret)
         goto err_free;
 
     blk_stat_add_callback(q, rwb->cb);
 
     rwb->min_lat_nsec = wbt_default_latency_nsec(q);
 
     wbt_queue_depth_changed(&rwb->rqos);
     wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
 
     return 0;
 
 err_free:
     blk_stat_free_callback(rwb->cb);
     kfree(rwb);
     return ret;
 
 }

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