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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Block rq-qos base io controller
  *
  * This works similar to wbt with a few exceptions
  *
  * - It's bio based, so the latency covers the whole block layer in addition to
  *   the actual io.
  * - We will throttle all IO that comes in here if we need to.
  * - We use the mean latency over the 100ms window.  This is because writes can
  *   be particularly fast, which could give us a false sense of the impact of
  *   other workloads on our protected workload.
  * - By default there's no throttling, we set the queue_depth to UINT_MAX so
  *   that we can have as many outstanding bio's as we're allowed to.  Only at
  *   throttle time do we pay attention to the actual queue depth.
  *
  * The hierarchy works like the cpu controller does, we track the latency at
  * every configured node, and each configured node has it's own independent
  * queue depth.  This means that we only care about our latency targets at the
  * peer level.  Some group at the bottom of the hierarchy isn't going to affect
  * a group at the end of some other path if we're only configred at leaf level.
  *
  * Consider the following
  *
  *                   root blkg
  *             /                     \
  *        fast (target=5ms)     slow (target=10ms)
  *         /     \                  /        \
  *       a        b          normal(15ms)   unloved
  *
  * "a" and "b" have no target, but their combined io under "fast" cannot exceed
  * an average latency of 5ms.  If it does then we will throttle the "slow"
  * group.  In the case of "normal", if it exceeds its 15ms target, we will
  * throttle "unloved", but nobody else.
  *
  * In this example "fast", "slow", and "normal" will be the only groups actually
  * accounting their io latencies.  We have to walk up the heirarchy to the root
  * on every submit and complete so we can do the appropriate stat recording and
  * adjust the queue depth of ourselves if needed.
  *
  * There are 2 ways we throttle IO.
  *
  * 1) Queue depth throttling.  As we throttle down we will adjust the maximum
  * number of IO's we're allowed to have in flight.  This starts at (u64)-1 down
  * to 1.  If the group is only ever submitting IO for itself then this is the
  * only way we throttle.
  *
  * 2) Induced delay throttling.  This is for the case that a group is generating
  * IO that has to be issued by the root cg to avoid priority inversion. So think
  * REQ_META or REQ_SWAP.  If we are already at qd == 1 and we're getting a lot
  * of work done for us on behalf of the root cg and are being asked to scale
  * down more then we induce a latency at userspace return.  We accumulate the
  * total amount of time we need to be punished by doing
  *
  * total_time += min_lat_nsec - actual_io_completion
  *
  * and then at throttle time will do
  *
  * throttle_time = min(total_time, NSEC_PER_SEC)
  *
  * This induced delay will throttle back the activity that is generating the
  * root cg issued io's, wethere that's some metadata intensive operation or the
  * group is using so much memory that it is pushing us into swap.
  *
  * Copyright (C) 2018 Josef Bacik
  */
 #include <linux/kernel.h>
 #include <linux/blk_types.h>
 #include <linux/backing-dev.h>
 #include <linux/module.h>
 #include <linux/timer.h>
 #include <linux/memcontrol.h>
 #include <linux/sched/loadavg.h>
 #include <linux/sched/signal.h>
 #include <trace/events/block.h>
 #include <linux/blk-mq.h>
 #include "blk-rq-qos.h"
 #include "blk-stat.h"
 #include "blk-cgroup.h"
 #include "blk.h"
 
 #define DEFAULT_SCALE_COOKIE 1000000U
 
 static struct blkcg_policy blkcg_policy_iolatency;
 struct iolatency_grp;
 
 struct blk_iolatency {
     struct rq_qos rqos;
     struct timer_list timer;
 
     /*
      * ->enabled is the master enable switch gating the throttling logic and
      * inflight tracking. The number of cgroups which have iolat enabled is
      * tracked in ->enable_cnt, and ->enable is flipped on/off accordingly
      * from ->enable_work with the request_queue frozen. For details, See
      * blkiolatency_enable_work_fn().
      */
     bool enabled;
     atomic_t enable_cnt;
     struct work_struct enable_work;
 };
 
 static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos)
 {
     return container_of(rqos, struct blk_iolatency, rqos);
 }
 
 struct child_latency_info {
     spinlock_t lock;
 
     /* Last time we adjusted the scale of everybody. */
     u64 last_scale_event;
 
     /* The latency that we missed. */
     u64 scale_lat;
 
     /* Total io's from all of our children for the last summation. */
     u64 nr_samples;
 
     /* The guy who actually changed the latency numbers. */
     struct iolatency_grp *scale_grp;
 
     /* Cookie to tell if we need to scale up or down. */
     atomic_t scale_cookie;
 };
 
 struct percentile_stats {
     u64 total;
     u64 missed;
 };
 
 struct latency_stat {
     union {
         struct percentile_stats ps;
         struct blk_rq_stat rqs;
     };
 };
 
 struct iolatency_grp {
     struct blkg_policy_data pd;
     struct latency_stat __percpu *stats;
     struct latency_stat cur_stat;
     struct blk_iolatency *blkiolat;
     struct rq_depth rq_depth;
     struct rq_wait rq_wait;
     atomic64_t window_start;
     atomic_t scale_cookie;
     u64 min_lat_nsec;
     u64 cur_win_nsec;
 
     /* total running average of our io latency. */
     u64 lat_avg;
 
     /* Our current number of IO's for the last summation. */
     u64 nr_samples;
 
     bool ssd;
     struct child_latency_info child_lat;
 };
 
 #define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC)
 #define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC
 /*
  * These are the constants used to fake the fixed-point moving average
  * calculation just like load average.  The call to calc_load() folds
  * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg.  The sampling
  * window size is bucketed to try to approximately calculate average
  * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows
  * elapse immediately.  Note, windows only elapse with IO activity.  Idle
  * periods extend the most recent window.
  */
 #define BLKIOLATENCY_NR_EXP_FACTORS 5
 #define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \
                       (BLKIOLATENCY_NR_EXP_FACTORS - 1))
 static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = {
     2045, // exp(1/600) - 600 samples
     2039, // exp(1/240) - 240 samples
     2031, // exp(1/120) - 120 samples
     2023, // exp(1/80)  - 80 samples
     2014, // exp(1/60)  - 60 samples
 };
 
 static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd)
 {
     return pd ? container_of(pd, struct iolatency_grp, pd) : NULL;
 }
 
 static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg)
 {
     return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency));
 }
 
 static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat)
 {
     return pd_to_blkg(&iolat->pd);
 }
 
 static inline void latency_stat_init(struct iolatency_grp *iolat,
                      struct latency_stat *stat)
 {
     if (iolat->ssd) {
         stat->ps.total = 0;
         stat->ps.missed = 0;
     } else
         blk_rq_stat_init(&stat->rqs);
 }
 
 static inline void latency_stat_sum(struct iolatency_grp *iolat,
                     struct latency_stat *sum,
                     struct latency_stat *stat)
 {
     if (iolat->ssd) {
         sum->ps.total += stat->ps.total;
         sum->ps.missed += stat->ps.missed;
     } else
         blk_rq_stat_sum(&sum->rqs, &stat->rqs);
 }
 
 static inline void latency_stat_record_time(struct iolatency_grp *iolat,
                         u64 req_time)
 {
     struct latency_stat *stat = get_cpu_ptr(iolat->stats);
     if (iolat->ssd) {
         if (req_time >= iolat->min_lat_nsec)
             stat->ps.missed++;
         stat->ps.total++;
     } else
         blk_rq_stat_add(&stat->rqs, req_time);
     put_cpu_ptr(stat);
 }
 
 static inline bool latency_sum_ok(struct iolatency_grp *iolat,
                   struct latency_stat *stat)
 {
     if (iolat->ssd) {
         u64 thresh = div64_u64(stat->ps.total, 10);
         thresh = max(thresh, 1ULL);
         return stat->ps.missed < thresh;
     }
     return stat->rqs.mean <= iolat->min_lat_nsec;
 }
 
 static inline u64 latency_stat_samples(struct iolatency_grp *iolat,
                        struct latency_stat *stat)
 {
     if (iolat->ssd)
         return stat->ps.total;
     return stat->rqs.nr_samples;
 }
 
 static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat,
                           struct latency_stat *stat)
 {
     int exp_idx;
 
     if (iolat->ssd)
         return;
 
     /*
      * calc_load() takes in a number stored in fixed point representation.
      * Because we are using this for IO time in ns, the values stored
      * are significantly larger than the FIXED_1 denominator (2048).
      * Therefore, rounding errors in the calculation are negligible and
      * can be ignored.
      */
     exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1,
             div64_u64(iolat->cur_win_nsec,
                   BLKIOLATENCY_EXP_BUCKET_SIZE));
     iolat->lat_avg = calc_load(iolat->lat_avg,
                    iolatency_exp_factors[exp_idx],
                    stat->rqs.mean);
 }
 
 static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data)
 {
     atomic_dec(&rqw->inflight);
     wake_up(&rqw->wait);
 }
 
 static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data)
 {
     struct iolatency_grp *iolat = private_data;
     return rq_wait_inc_below(rqw, iolat->rq_depth.max_depth);
 }
 
 static void __blkcg_iolatency_throttle(struct rq_qos *rqos,
                        struct iolatency_grp *iolat,
                        bool issue_as_root,
                        bool use_memdelay)
 {
     struct rq_wait *rqw = &iolat->rq_wait;
     unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay);
 
     if (use_delay)
         blkcg_schedule_throttle(rqos->q, use_memdelay);
 
     /*
      * To avoid priority inversions we want to just take a slot if we are
      * issuing as root.  If we're being killed off there's no point in
      * delaying things, we may have been killed by OOM so throttling may
      * make recovery take even longer, so just let the IO's through so the
      * task can go away.
      */
     if (issue_as_root || fatal_signal_pending(current)) {
         atomic_inc(&rqw->inflight);
         return;
     }
 
     rq_qos_wait(rqw, iolat, iolat_acquire_inflight, iolat_cleanup_cb);
 }
 
 #define SCALE_DOWN_FACTOR 2
 #define SCALE_UP_FACTOR 4
 
 static inline unsigned long scale_amount(unsigned long qd, bool up)
 {
     return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL);
 }
 
 /*
  * We scale the qd down faster than we scale up, so we need to use this helper
  * to adjust the scale_cookie accordingly so we don't prematurely get
  * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much.
  *
  * Each group has their own local copy of the last scale cookie they saw, so if
  * the global scale cookie goes up or down they know which way they need to go
  * based on their last knowledge of it.
  */
 static void scale_cookie_change(struct blk_iolatency *blkiolat,
                 struct child_latency_info *lat_info,
                 bool up)
 {
     unsigned long qd = blkiolat->rqos.q->nr_requests;
     unsigned long scale = scale_amount(qd, up);
     unsigned long old = atomic_read(&lat_info->scale_cookie);
     unsigned long max_scale = qd << 1;
     unsigned long diff = 0;
 
     if (old < DEFAULT_SCALE_COOKIE)
         diff = DEFAULT_SCALE_COOKIE - old;
 
     if (up) {
         if (scale + old > DEFAULT_SCALE_COOKIE)
             atomic_set(&lat_info->scale_cookie,
                    DEFAULT_SCALE_COOKIE);
         else if (diff > qd)
             atomic_inc(&lat_info->scale_cookie);
         else
             atomic_add(scale, &lat_info->scale_cookie);
     } else {
         /*
          * We don't want to dig a hole so deep that it takes us hours to
          * dig out of it.  Just enough that we don't throttle/unthrottle
          * with jagged workloads but can still unthrottle once pressure
          * has sufficiently dissipated.
          */
         if (diff > qd) {
             if (diff < max_scale)
                 atomic_dec(&lat_info->scale_cookie);
         } else {
             atomic_sub(scale, &lat_info->scale_cookie);
         }
     }
 }
 
 /*
  * Change the queue depth of the iolatency_grp.  We add/subtract 1/16th of the
  * queue depth at a time so we don't get wild swings and hopefully dial in to
  * fairer distribution of the overall queue depth.
  */
 static void scale_change(struct iolatency_grp *iolat, bool up)
 {
     unsigned long qd = iolat->blkiolat->rqos.q->nr_requests;
     unsigned long scale = scale_amount(qd, up);
     unsigned long old = iolat->rq_depth.max_depth;
 
     if (old > qd)
         old = qd;
 
     if (up) {
         if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat)))
             return;
 
         if (old < qd) {
             old += scale;
             old = min(old, qd);
             iolat->rq_depth.max_depth = old;
             wake_up_all(&iolat->rq_wait.wait);
         }
     } else {
         old >>= 1;
         iolat->rq_depth.max_depth = max(old, 1UL);
     }
 }
 
 /* Check our parent and see if the scale cookie has changed. */
 static void check_scale_change(struct iolatency_grp *iolat)
 {
     struct iolatency_grp *parent;
     struct child_latency_info *lat_info;
     unsigned int cur_cookie;
     unsigned int our_cookie = atomic_read(&iolat->scale_cookie);
     u64 scale_lat;
     int direction = 0;
 
     if (lat_to_blkg(iolat)->parent == NULL)
         return;
 
     parent = blkg_to_lat(lat_to_blkg(iolat)->parent);
     if (!parent)
         return;
 
     lat_info = &parent->child_lat;
     cur_cookie = atomic_read(&lat_info->scale_cookie);
     scale_lat = READ_ONCE(lat_info->scale_lat);
 
     if (cur_cookie < our_cookie)
         direction = -1;
     else if (cur_cookie > our_cookie)
         direction = 1;
     else
         return;
 
     if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) {
         /* Somebody beat us to the punch, just bail. */
         return;
     }
 
     if (direction < 0 && iolat->min_lat_nsec) {
         u64 samples_thresh;
 
         if (!scale_lat || iolat->min_lat_nsec <= scale_lat)
             return;
 
         /*
          * Sometimes high priority groups are their own worst enemy, so
          * instead of taking it out on some poor other group that did 5%
          * or less of the IO's for the last summation just skip this
          * scale down event.
          */
         samples_thresh = lat_info->nr_samples * 5;
         samples_thresh = max(1ULL, div64_u64(samples_thresh, 100));
         if (iolat->nr_samples <= samples_thresh)
             return;
     }
 
     /* We're as low as we can go. */
     if (iolat->rq_depth.max_depth == 1 && direction < 0) {
         blkcg_use_delay(lat_to_blkg(iolat));
         return;
     }
 
     /* We're back to the default cookie, unthrottle all the things. */
     if (cur_cookie == DEFAULT_SCALE_COOKIE) {
         blkcg_clear_delay(lat_to_blkg(iolat));
         iolat->rq_depth.max_depth = UINT_MAX;
         wake_up_all(&iolat->rq_wait.wait);
         return;
     }
 
     scale_change(iolat, direction > 0);
 }
 
 static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio)
 {
     struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
     struct blkcg_gq *blkg = bio->bi_blkg;
     bool issue_as_root = bio_issue_as_root_blkg(bio);
 
     if (!blkiolat->enabled)
         return;
 
     while (blkg && blkg->parent) {
         struct iolatency_grp *iolat = blkg_to_lat(blkg);
         if (!iolat) {
             blkg = blkg->parent;
             continue;
         }
 
         check_scale_change(iolat);
         __blkcg_iolatency_throttle(rqos, iolat, issue_as_root,
                      (bio->bi_opf & REQ_SWAP) == REQ_SWAP);
         blkg = blkg->parent;
     }
     if (!timer_pending(&blkiolat->timer))
         mod_timer(&blkiolat->timer, jiffies + HZ);
 }
 
 static void iolatency_record_time(struct iolatency_grp *iolat,
                   struct bio_issue *issue, u64 now,
                   bool issue_as_root)
 {
     u64 start = bio_issue_time(issue);
     u64 req_time;
 
     /*
      * Have to do this so we are truncated to the correct time that our
      * issue is truncated to.
      */
     now = __bio_issue_time(now);
 
     if (now <= start)
         return;
 
     req_time = now - start;
 
     /*
      * We don't want to count issue_as_root bio's in the cgroups latency
      * statistics as it could skew the numbers downwards.
      */
     if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) {
         u64 sub = iolat->min_lat_nsec;
         if (req_time < sub)
             blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time);
         return;
     }
 
     latency_stat_record_time(iolat, req_time);
 }
 
 #define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC)
 #define BLKIOLATENCY_MIN_GOOD_SAMPLES 5
 
 static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
 {
     struct blkcg_gq *blkg = lat_to_blkg(iolat);
     struct iolatency_grp *parent;
     struct child_latency_info *lat_info;
     struct latency_stat stat;
     unsigned long flags;
     int cpu;
 
     latency_stat_init(iolat, &stat);
     preempt_disable();
     for_each_online_cpu(cpu) {
         struct latency_stat *s;
         s = per_cpu_ptr(iolat->stats, cpu);
         latency_stat_sum(iolat, &stat, s);
         latency_stat_init(iolat, s);
     }
     preempt_enable();
 
     parent = blkg_to_lat(blkg->parent);
     if (!parent)
         return;
 
     lat_info = &parent->child_lat;
 
     iolat_update_total_lat_avg(iolat, &stat);
 
     /* Everything is ok and we don't need to adjust the scale. */
     if (latency_sum_ok(iolat, &stat) &&
         atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE)
         return;
 
     /* Somebody beat us to the punch, just bail. */
     spin_lock_irqsave(&lat_info->lock, flags);
 
     latency_stat_sum(iolat, &iolat->cur_stat, &stat);
     lat_info->nr_samples -= iolat->nr_samples;
     lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat);
     iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat);
 
     if ((lat_info->last_scale_event >= now ||
         now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME))
         goto out;
 
     if (latency_sum_ok(iolat, &iolat->cur_stat) &&
         latency_sum_ok(iolat, &stat)) {
         if (latency_stat_samples(iolat, &iolat->cur_stat) <
             BLKIOLATENCY_MIN_GOOD_SAMPLES)
             goto out;
         if (lat_info->scale_grp == iolat) {
             lat_info->last_scale_event = now;
             scale_cookie_change(iolat->blkiolat, lat_info, true);
         }
     } else if (lat_info->scale_lat == 0 ||
            lat_info->scale_lat >= iolat->min_lat_nsec) {
         lat_info->last_scale_event = now;
         if (!lat_info->scale_grp ||
             lat_info->scale_lat > iolat->min_lat_nsec) {
             WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec);
             lat_info->scale_grp = iolat;
         }
         scale_cookie_change(iolat->blkiolat, lat_info, false);
     }
     latency_stat_init(iolat, &iolat->cur_stat);
 out:
     spin_unlock_irqrestore(&lat_info->lock, flags);
 }
 
 static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
 {
     struct blkcg_gq *blkg;
     struct rq_wait *rqw;
     struct iolatency_grp *iolat;
     u64 window_start;
     u64 now;
     bool issue_as_root = bio_issue_as_root_blkg(bio);
     int inflight = 0;
 
     blkg = bio->bi_blkg;
     if (!blkg || !bio_flagged(bio, BIO_QOS_THROTTLED))
         return;
 
     iolat = blkg_to_lat(bio->bi_blkg);
     if (!iolat)
         return;
 
     if (!iolat->blkiolat->enabled)
         return;
 
     now = ktime_to_ns(ktime_get());
     while (blkg && blkg->parent) {
         iolat = blkg_to_lat(blkg);
         if (!iolat) {
             blkg = blkg->parent;
             continue;
         }
         rqw = &iolat->rq_wait;
 
         inflight = atomic_dec_return(&rqw->inflight);
         WARN_ON_ONCE(inflight < 0);
         /*
          * If bi_status is BLK_STS_AGAIN, the bio wasn't actually
          * submitted, so do not account for it.
          */
         if (iolat->min_lat_nsec && bio->bi_status != BLK_STS_AGAIN) {
             iolatency_record_time(iolat, &bio->bi_issue, now,
                           issue_as_root);
             window_start = atomic64_read(&iolat->window_start);
             if (now > window_start &&
                 (now - window_start) >= iolat->cur_win_nsec) {
                 if (atomic64_try_cmpxchg(&iolat->window_start,
                              &window_start, now))
                     iolatency_check_latencies(iolat, now);
             }
         }
         wake_up(&rqw->wait);
         blkg = blkg->parent;
     }
 }
 
 static void blkcg_iolatency_exit(struct rq_qos *rqos)
 {
     struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
 
     del_timer_sync(&blkiolat->timer);
     flush_work(&blkiolat->enable_work);
     blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency);
     kfree(blkiolat);
 }
 
 static struct rq_qos_ops blkcg_iolatency_ops = {
     .throttle = blkcg_iolatency_throttle,
     .done_bio = blkcg_iolatency_done_bio,
     .exit = blkcg_iolatency_exit,
 };
 
 static void blkiolatency_timer_fn(struct timer_list *t)
 {
     struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer);
     struct blkcg_gq *blkg;
     struct cgroup_subsys_state *pos_css;
     u64 now = ktime_to_ns(ktime_get());
 
     rcu_read_lock();
     blkg_for_each_descendant_pre(blkg, pos_css,
                      blkiolat->rqos.q->root_blkg) {
         struct iolatency_grp *iolat;
         struct child_latency_info *lat_info;
         unsigned long flags;
         u64 cookie;
 
         /*
          * We could be exiting, don't access the pd unless we have a
          * ref on the blkg.
          */
         if (!blkg_tryget(blkg))
             continue;
 
         iolat = blkg_to_lat(blkg);
         if (!iolat)
             goto next;
 
         lat_info = &iolat->child_lat;
         cookie = atomic_read(&lat_info->scale_cookie);
 
         if (cookie >= DEFAULT_SCALE_COOKIE)
             goto next;
 
         spin_lock_irqsave(&lat_info->lock, flags);
         if (lat_info->last_scale_event >= now)
             goto next_lock;
 
         /*
          * We scaled down but don't have a scale_grp, scale up and carry
          * on.
          */
         if (lat_info->scale_grp == NULL) {
             scale_cookie_change(iolat->blkiolat, lat_info, true);
             goto next_lock;
         }
 
         /*
          * It's been 5 seconds since our last scale event, clear the
          * scale grp in case the group that needed the scale down isn't
          * doing any IO currently.
          */
         if (now - lat_info->last_scale_event >=
             ((u64)NSEC_PER_SEC * 5))
             lat_info->scale_grp = NULL;
 next_lock:
         spin_unlock_irqrestore(&lat_info->lock, flags);
 next:
         blkg_put(blkg);
     }
     rcu_read_unlock();
 }
 
 /**
  * blkiolatency_enable_work_fn - Enable or disable iolatency on the device
  * @work: enable_work of the blk_iolatency of interest
  *
  * iolatency needs to keep track of the number of in-flight IOs per cgroup. This
  * is relatively expensive as it involves walking up the hierarchy twice for
  * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we
  * want to disable the in-flight tracking.
  *
  * We have to make sure that the counting is balanced - we don't want to leak
  * the in-flight counts by disabling accounting in the completion path while IOs
  * are in flight. This is achieved by ensuring that no IO is in flight by
  * freezing the queue while flipping ->enabled. As this requires a sleepable
  * context, ->enabled flipping is punted to this work function.
  */
 static void blkiolatency_enable_work_fn(struct work_struct *work)
 {
     struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency,
                               enable_work);
     bool enabled;
 
     /*
      * There can only be one instance of this function running for @blkiolat
      * and it's guaranteed to be executed at least once after the latest
      * ->enabled_cnt modification. Acting on the latest ->enable_cnt is
      * sufficient.
      *
      * Also, we know @blkiolat is safe to access as ->enable_work is flushed
      * in blkcg_iolatency_exit().
      */
     enabled = atomic_read(&blkiolat->enable_cnt);
     if (enabled != blkiolat->enabled) {
         blk_mq_freeze_queue(blkiolat->rqos.q);
         blkiolat->enabled = enabled;
         blk_mq_unfreeze_queue(blkiolat->rqos.q);
     }
 }
 
 int blk_iolatency_init(struct request_queue *q)
 {
     struct blk_iolatency *blkiolat;
     struct rq_qos *rqos;
     int ret;
 
     blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL);
     if (!blkiolat)
         return -ENOMEM;
 
     rqos = &blkiolat->rqos;
     rqos->id = RQ_QOS_LATENCY;
     rqos->ops = &blkcg_iolatency_ops;
     rqos->q = q;
 
     ret = rq_qos_add(q, rqos);
     if (ret)
         goto err_free;
     ret = blkcg_activate_policy(q, &blkcg_policy_iolatency);
     if (ret)
         goto err_qos_del;
 
     timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0);
     INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn);
 
     return 0;
 
 err_qos_del:
     rq_qos_del(q, rqos);
 err_free:
     kfree(blkiolat);
     return ret;
 }
 
 static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val)
 {
     struct iolatency_grp *iolat = blkg_to_lat(blkg);
     struct blk_iolatency *blkiolat = iolat->blkiolat;
     u64 oldval = iolat->min_lat_nsec;
 
     iolat->min_lat_nsec = val;
     iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE);
     iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec,
                     BLKIOLATENCY_MAX_WIN_SIZE);
 
     if (!oldval && val) {
         if (atomic_inc_return(&blkiolat->enable_cnt) == 1)
             schedule_work(&blkiolat->enable_work);
     }
     if (oldval && !val) {
         blkcg_clear_delay(blkg);
         if (atomic_dec_return(&blkiolat->enable_cnt) == 0)
             schedule_work(&blkiolat->enable_work);
     }
 }
 
 static void iolatency_clear_scaling(struct blkcg_gq *blkg)
 {
     if (blkg->parent) {
         struct iolatency_grp *iolat = blkg_to_lat(blkg->parent);
         struct child_latency_info *lat_info;
         if (!iolat)
             return;
 
         lat_info = &iolat->child_lat;
         spin_lock(&lat_info->lock);
         atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE);
         lat_info->last_scale_event = 0;
         lat_info->scale_grp = NULL;
         lat_info->scale_lat = 0;
         spin_unlock(&lat_info->lock);
     }
 }
 
 static ssize_t iolatency_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 blkcg_gq *blkg;
     struct blkg_conf_ctx ctx;
     struct iolatency_grp *iolat;
     char *p, *tok;
     u64 lat_val = 0;
     u64 oldval;
     int ret;
 
     ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx);
     if (ret)
         return ret;
 
     iolat = blkg_to_lat(ctx.blkg);
     p = ctx.body;
 
     ret = -EINVAL;
     while ((tok = strsep(&p, " "))) {
         char key[16];
         char val[21];   /* 18446744073709551616 */
 
         if (sscanf(tok, "%15[^=]=%20s", key, val) != 2)
             goto out;
 
         if (!strcmp(key, "target")) {
             u64 v;
 
             if (!strcmp(val, "max"))
                 lat_val = 0;
             else if (sscanf(val, "%llu", &v) == 1)
                 lat_val = v * NSEC_PER_USEC;
             else
                 goto out;
         } else {
             goto out;
         }
     }
 
     /* Walk up the tree to see if our new val is lower than it should be. */
     blkg = ctx.blkg;
     oldval = iolat->min_lat_nsec;
 
     iolatency_set_min_lat_nsec(blkg, lat_val);
     if (oldval != iolat->min_lat_nsec)
         iolatency_clear_scaling(blkg);
     ret = 0;
 out:
     blkg_conf_finish(&ctx);
     return ret ?: nbytes;
 }
 
 static u64 iolatency_prfill_limit(struct seq_file *sf,
                   struct blkg_policy_data *pd, int off)
 {
     struct iolatency_grp *iolat = pd_to_lat(pd);
     const char *dname = blkg_dev_name(pd->blkg);
 
     if (!dname || !iolat->min_lat_nsec)
         return 0;
     seq_printf(sf, "%s target=%llu\n",
            dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC));
     return 0;
 }
 
 static int iolatency_print_limit(struct seq_file *sf, void *v)
 {
     blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
               iolatency_prfill_limit,
               &blkcg_policy_iolatency, seq_cft(sf)->private, false);
     return 0;
 }
 
 static void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s)
 {
     struct latency_stat stat;
     int cpu;
 
     latency_stat_init(iolat, &stat);
     preempt_disable();
     for_each_online_cpu(cpu) {
         struct latency_stat *s;
         s = per_cpu_ptr(iolat->stats, cpu);
         latency_stat_sum(iolat, &stat, s);
     }
     preempt_enable();
 
     if (iolat->rq_depth.max_depth == UINT_MAX)
         seq_printf(s, " missed=%llu total=%llu depth=max",
             (unsigned long long)stat.ps.missed,
             (unsigned long long)stat.ps.total);
     else
         seq_printf(s, " missed=%llu total=%llu depth=%u",
             (unsigned long long)stat.ps.missed,
             (unsigned long long)stat.ps.total,
             iolat->rq_depth.max_depth);
 }
 
 static void iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 {
     struct iolatency_grp *iolat = pd_to_lat(pd);
     unsigned long long avg_lat;
     unsigned long long cur_win;
 
     if (!blkcg_debug_stats)
         return;
 
     if (iolat->ssd)
         return iolatency_ssd_stat(iolat, s);
 
     avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC);
     cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC);
     if (iolat->rq_depth.max_depth == UINT_MAX)
         seq_printf(s, " depth=max avg_lat=%llu win=%llu",
             avg_lat, cur_win);
     else
         seq_printf(s, " depth=%u avg_lat=%llu win=%llu",
             iolat->rq_depth.max_depth, avg_lat, cur_win);
 }
 
 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp,
                            struct request_queue *q,
                            struct blkcg *blkcg)
 {
     struct iolatency_grp *iolat;
 
     iolat = kzalloc_node(sizeof(*iolat), gfp, q->node);
     if (!iolat)
         return NULL;
     iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat),
                        __alignof__(struct latency_stat), gfp);
     if (!iolat->stats) {
         kfree(iolat);
         return NULL;
     }
     return &iolat->pd;
 }
 
 static void iolatency_pd_init(struct blkg_policy_data *pd)
 {
     struct iolatency_grp *iolat = pd_to_lat(pd);
     struct blkcg_gq *blkg = lat_to_blkg(iolat);
     struct rq_qos *rqos = blkcg_rq_qos(blkg->q);
     struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
     u64 now = ktime_to_ns(ktime_get());
     int cpu;
 
     if (blk_queue_nonrot(blkg->q))
         iolat->ssd = true;
     else
         iolat->ssd = false;
 
     for_each_possible_cpu(cpu) {
         struct latency_stat *stat;
         stat = per_cpu_ptr(iolat->stats, cpu);
         latency_stat_init(iolat, stat);
     }
 
     latency_stat_init(iolat, &iolat->cur_stat);
     rq_wait_init(&iolat->rq_wait);
     spin_lock_init(&iolat->child_lat.lock);
     iolat->rq_depth.queue_depth = blkg->q->nr_requests;
     iolat->rq_depth.max_depth = UINT_MAX;
     iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth;
     iolat->blkiolat = blkiolat;
     iolat->cur_win_nsec = 100 * NSEC_PER_MSEC;
     atomic64_set(&iolat->window_start, now);
 
     /*
      * We init things in list order, so the pd for the parent may not be
      * init'ed yet for whatever reason.
      */
     if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) {
         struct iolatency_grp *parent = blkg_to_lat(blkg->parent);
         atomic_set(&iolat->scale_cookie,
                atomic_read(&parent->child_lat.scale_cookie));
     } else {
         atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE);
     }
 
     atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE);
 }
 
 static void iolatency_pd_offline(struct blkg_policy_data *pd)
 {
     struct iolatency_grp *iolat = pd_to_lat(pd);
     struct blkcg_gq *blkg = lat_to_blkg(iolat);
 
     iolatency_set_min_lat_nsec(blkg, 0);
     iolatency_clear_scaling(blkg);
 }
 
 static void iolatency_pd_free(struct blkg_policy_data *pd)
 {
     struct iolatency_grp *iolat = pd_to_lat(pd);
     free_percpu(iolat->stats);
     kfree(iolat);
 }
 
 static struct cftype iolatency_files[] = {
     {
         .name = "latency",
         .flags = CFTYPE_NOT_ON_ROOT,
         .seq_show = iolatency_print_limit,
         .write = iolatency_set_limit,
     },
     {}
 };
 
 static struct blkcg_policy blkcg_policy_iolatency = {
     .dfl_cftypes    = iolatency_files,
     .pd_alloc_fn    = iolatency_pd_alloc,
     .pd_init_fn = iolatency_pd_init,
     .pd_offline_fn  = iolatency_pd_offline,
     .pd_free_fn = iolatency_pd_free,
     .pd_stat_fn = iolatency_pd_stat,
 };
 
 static int __init iolatency_init(void)
 {
     return blkcg_policy_register(&blkcg_policy_iolatency);
 }
 
 static void __exit iolatency_exit(void)
 {
     blkcg_policy_unregister(&blkcg_policy_iolatency);
 }
 
 module_init(iolatency_init);
 module_exit(iolatency_exit);

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