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 // SPDX-License-Identifier: GPL-2.0
 /*
  * Data Access Monitor
  *
  * Author: SeongJae Park <sjpark@amazon.de>
  */
 
 #define pr_fmt(fmt) "damon: " fmt
 
 #include <linux/damon.h>
 #include <linux/delay.h>
 #include <linux/kthread.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/damon.h>
 
 #ifdef CONFIG_DAMON_KUNIT_TEST
 #undef DAMON_MIN_REGION
 #define DAMON_MIN_REGION 1
 #endif
 
 static DEFINE_MUTEX(damon_lock);
 static int nr_running_ctxs;
 static bool running_exclusive_ctxs;
 
 static DEFINE_MUTEX(damon_ops_lock);
 static struct damon_operations damon_registered_ops[NR_DAMON_OPS];
 
 /* Should be called under damon_ops_lock with id smaller than NR_DAMON_OPS */
 static bool __damon_is_registered_ops(enum damon_ops_id id)
 {
     struct damon_operations empty_ops = {};
 
     if (!memcmp(&empty_ops, &damon_registered_ops[id], sizeof(empty_ops)))
         return false;
     return true;
 }
 
 /**
  * damon_is_registered_ops() - Check if a given damon_operations is registered.
  * @id: Id of the damon_operations to check if registered.
  *
  * Return: true if the ops is set, false otherwise.
  */
 bool damon_is_registered_ops(enum damon_ops_id id)
 {
     bool registered;
 
     if (id >= NR_DAMON_OPS)
         return false;
     mutex_lock(&damon_ops_lock);
     registered = __damon_is_registered_ops(id);
     mutex_unlock(&damon_ops_lock);
     return registered;
 }
 
 /**
  * damon_register_ops() - Register a monitoring operations set to DAMON.
  * @ops:    monitoring operations set to register.
  *
  * This function registers a monitoring operations set of valid &struct
  * damon_operations->id so that others can find and use them later.
  *
  * Return: 0 on success, negative error code otherwise.
  */
 int damon_register_ops(struct damon_operations *ops)
 {
     int err = 0;
 
     if (ops->id >= NR_DAMON_OPS)
         return -EINVAL;
     mutex_lock(&damon_ops_lock);
     /* Fail for already registered ops */
     if (__damon_is_registered_ops(ops->id)) {
         err = -EINVAL;
         goto out;
     }
     damon_registered_ops[ops->id] = *ops;
 out:
     mutex_unlock(&damon_ops_lock);
     return err;
 }
 
 /**
  * damon_select_ops() - Select a monitoring operations to use with the context.
  * @ctx:    monitoring context to use the operations.
  * @id:     id of the registered monitoring operations to select.
  *
  * This function finds registered monitoring operations set of @id and make
  * @ctx to use it.
  *
  * Return: 0 on success, negative error code otherwise.
  */
 int damon_select_ops(struct damon_ctx *ctx, enum damon_ops_id id)
 {
     int err = 0;
 
     if (id >= NR_DAMON_OPS)
         return -EINVAL;
 
     mutex_lock(&damon_ops_lock);
     if (!__damon_is_registered_ops(id))
         err = -EINVAL;
     else
         ctx->ops = damon_registered_ops[id];
     mutex_unlock(&damon_ops_lock);
     return err;
 }
 
 /*
  * Construct a damon_region struct
  *
  * Returns the pointer to the new struct if success, or NULL otherwise
  */
 struct damon_region *damon_new_region(unsigned long start, unsigned long end)
 {
     struct damon_region *region;
 
     region = kmalloc(sizeof(*region), GFP_KERNEL);
     if (!region)
         return NULL;
 
     region->ar.start = start;
     region->ar.end = end;
     region->nr_accesses = 0;
     INIT_LIST_HEAD(&region->list);
 
     region->age = 0;
     region->last_nr_accesses = 0;
 
     return region;
 }
 
 void damon_add_region(struct damon_region *r, struct damon_target *t)
 {
     list_add_tail(&r->list, &t->regions_list);
     t->nr_regions++;
 }
 
 static void damon_del_region(struct damon_region *r, struct damon_target *t)
 {
     list_del(&r->list);
     t->nr_regions--;
 }
 
 static void damon_free_region(struct damon_region *r)
 {
     kfree(r);
 }
 
 void damon_destroy_region(struct damon_region *r, struct damon_target *t)
 {
     damon_del_region(r, t);
     damon_free_region(r);
 }
 
 /*
  * Check whether a region is intersecting an address range
  *
  * Returns true if it is.
  */
 static bool damon_intersect(struct damon_region *r,
         struct damon_addr_range *re)
 {
     return !(r->ar.end <= re->start || re->end <= r->ar.start);
 }
 
 /*
  * damon_set_regions() - Set regions of a target for given address ranges.
  * @t:      the given target.
  * @ranges: array of new monitoring target ranges.
  * @nr_ranges:  length of @ranges.
  *
  * This function adds new regions to, or modify existing regions of a
  * monitoring target to fit in specific ranges.
  *
  * Return: 0 if success, or negative error code otherwise.
  */
 int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
         unsigned int nr_ranges)
 {
     struct damon_region *r, *next;
     unsigned int i;
 
     /* Remove regions which are not in the new ranges */
     damon_for_each_region_safe(r, next, t) {
         for (i = 0; i < nr_ranges; i++) {
             if (damon_intersect(r, &ranges[i]))
                 break;
         }
         if (i == nr_ranges)
             damon_destroy_region(r, t);
     }
 
     /* Add new regions or resize existing regions to fit in the ranges */
     for (i = 0; i < nr_ranges; i++) {
         struct damon_region *first = NULL, *last, *newr;
         struct damon_addr_range *range;
 
         range = &ranges[i];
         /* Get the first/last regions intersecting with the range */
         damon_for_each_region(r, t) {
             if (damon_intersect(r, range)) {
                 if (!first)
                     first = r;
                 last = r;
             }
             if (r->ar.start >= range->end)
                 break;
         }
         if (!first) {
             /* no region intersects with this range */
             newr = damon_new_region(
                     ALIGN_DOWN(range->start,
                         DAMON_MIN_REGION),
                     ALIGN(range->end, DAMON_MIN_REGION));
             if (!newr)
                 return -ENOMEM;
             damon_insert_region(newr, damon_prev_region(r), r, t);
         } else {
             /* resize intersecting regions to fit in this range */
             first->ar.start = ALIGN_DOWN(range->start,
                     DAMON_MIN_REGION);
             last->ar.end = ALIGN(range->end, DAMON_MIN_REGION);
         }
     }
     return 0;
 }
 
 struct damos *damon_new_scheme(
         unsigned long min_sz_region, unsigned long max_sz_region,
         unsigned int min_nr_accesses, unsigned int max_nr_accesses,
         unsigned int min_age_region, unsigned int max_age_region,
         enum damos_action action, struct damos_quota *quota,
         struct damos_watermarks *wmarks)
 {
     struct damos *scheme;
 
     scheme = kmalloc(sizeof(*scheme), GFP_KERNEL);
     if (!scheme)
         return NULL;
     scheme->min_sz_region = min_sz_region;
     scheme->max_sz_region = max_sz_region;
     scheme->min_nr_accesses = min_nr_accesses;
     scheme->max_nr_accesses = max_nr_accesses;
     scheme->min_age_region = min_age_region;
     scheme->max_age_region = max_age_region;
     scheme->action = action;
     scheme->stat = (struct damos_stat){};
     INIT_LIST_HEAD(&scheme->list);
 
     scheme->quota.ms = quota->ms;
     scheme->quota.sz = quota->sz;
     scheme->quota.reset_interval = quota->reset_interval;
     scheme->quota.weight_sz = quota->weight_sz;
     scheme->quota.weight_nr_accesses = quota->weight_nr_accesses;
     scheme->quota.weight_age = quota->weight_age;
     scheme->quota.total_charged_sz = 0;
     scheme->quota.total_charged_ns = 0;
     scheme->quota.esz = 0;
     scheme->quota.charged_sz = 0;
     scheme->quota.charged_from = 0;
     scheme->quota.charge_target_from = NULL;
     scheme->quota.charge_addr_from = 0;
 
     scheme->wmarks.metric = wmarks->metric;
     scheme->wmarks.interval = wmarks->interval;
     scheme->wmarks.high = wmarks->high;
     scheme->wmarks.mid = wmarks->mid;
     scheme->wmarks.low = wmarks->low;
     scheme->wmarks.activated = true;
 
     return scheme;
 }
 
 void damon_add_scheme(struct damon_ctx *ctx, struct damos *s)
 {
     list_add_tail(&s->list, &ctx->schemes);
 }
 
 static void damon_del_scheme(struct damos *s)
 {
     list_del(&s->list);
 }
 
 static void damon_free_scheme(struct damos *s)
 {
     kfree(s);
 }
 
 void damon_destroy_scheme(struct damos *s)
 {
     damon_del_scheme(s);
     damon_free_scheme(s);
 }
 
 /*
  * Construct a damon_target struct
  *
  * Returns the pointer to the new struct if success, or NULL otherwise
  */
 struct damon_target *damon_new_target(void)
 {
     struct damon_target *t;
 
     t = kmalloc(sizeof(*t), GFP_KERNEL);
     if (!t)
         return NULL;
 
     t->pid = NULL;
     t->nr_regions = 0;
     INIT_LIST_HEAD(&t->regions_list);
 
     return t;
 }
 
 void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
 {
     list_add_tail(&t->list, &ctx->adaptive_targets);
 }
 
 bool damon_targets_empty(struct damon_ctx *ctx)
 {
     return list_empty(&ctx->adaptive_targets);
 }
 
 static void damon_del_target(struct damon_target *t)
 {
     list_del(&t->list);
 }
 
 void damon_free_target(struct damon_target *t)
 {
     struct damon_region *r, *next;
 
     damon_for_each_region_safe(r, next, t)
         damon_free_region(r);
     kfree(t);
 }
 
 void damon_destroy_target(struct damon_target *t)
 {
     damon_del_target(t);
     damon_free_target(t);
 }
 
 unsigned int damon_nr_regions(struct damon_target *t)
 {
     return t->nr_regions;
 }
 
 struct damon_ctx *damon_new_ctx(void)
 {
     struct damon_ctx *ctx;
 
     ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
     if (!ctx)
         return NULL;
 
     ctx->sample_interval = 5 * 1000;
     ctx->aggr_interval = 100 * 1000;
     ctx->ops_update_interval = 60 * 1000 * 1000;
 
     ktime_get_coarse_ts64(&ctx->last_aggregation);
     ctx->last_ops_update = ctx->last_aggregation;
 
     mutex_init(&ctx->kdamond_lock);
 
     ctx->min_nr_regions = 10;
     ctx->max_nr_regions = 1000;
 
     INIT_LIST_HEAD(&ctx->adaptive_targets);
     INIT_LIST_HEAD(&ctx->schemes);
 
     return ctx;
 }
 
 static void damon_destroy_targets(struct damon_ctx *ctx)
 {
     struct damon_target *t, *next_t;
 
     if (ctx->ops.cleanup) {
         ctx->ops.cleanup(ctx);
         return;
     }
 
     damon_for_each_target_safe(t, next_t, ctx)
         damon_destroy_target(t);
 }
 
 void damon_destroy_ctx(struct damon_ctx *ctx)
 {
     struct damos *s, *next_s;
 
     damon_destroy_targets(ctx);
 
     damon_for_each_scheme_safe(s, next_s, ctx)
         damon_destroy_scheme(s);
 
     kfree(ctx);
 }
 
 /**
  * damon_set_attrs() - Set attributes for the monitoring.
  * @ctx:        monitoring context
  * @sample_int:     time interval between samplings
  * @aggr_int:       time interval between aggregations
  * @ops_upd_int:    time interval between monitoring operations updates
  * @min_nr_reg:     minimal number of regions
  * @max_nr_reg:     maximum number of regions
  *
  * This function should not be called while the kdamond is running.
  * Every time interval is in micro-seconds.
  *
  * Return: 0 on success, negative error code otherwise.
  */
 int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
             unsigned long aggr_int, unsigned long ops_upd_int,
             unsigned long min_nr_reg, unsigned long max_nr_reg)
 {
     if (min_nr_reg < 3)
         return -EINVAL;
     if (min_nr_reg > max_nr_reg)
         return -EINVAL;
 
     ctx->sample_interval = sample_int;
     ctx->aggr_interval = aggr_int;
     ctx->ops_update_interval = ops_upd_int;
     ctx->min_nr_regions = min_nr_reg;
     ctx->max_nr_regions = max_nr_reg;
 
     return 0;
 }
 
 /**
  * damon_set_schemes() - Set data access monitoring based operation schemes.
  * @ctx:    monitoring context
  * @schemes:    array of the schemes
  * @nr_schemes: number of entries in @schemes
  *
  * This function should not be called while the kdamond of the context is
  * running.
  *
  * Return: 0 if success, or negative error code otherwise.
  */
 int damon_set_schemes(struct damon_ctx *ctx, struct damos **schemes,
             ssize_t nr_schemes)
 {
     struct damos *s, *next;
     ssize_t i;
 
     damon_for_each_scheme_safe(s, next, ctx)
         damon_destroy_scheme(s);
     for (i = 0; i < nr_schemes; i++)
         damon_add_scheme(ctx, schemes[i]);
     return 0;
 }
 
 /**
  * damon_nr_running_ctxs() - Return number of currently running contexts.
  */
 int damon_nr_running_ctxs(void)
 {
     int nr_ctxs;
 
     mutex_lock(&damon_lock);
     nr_ctxs = nr_running_ctxs;
     mutex_unlock(&damon_lock);
 
     return nr_ctxs;
 }
 
 /* Returns the size upper limit for each monitoring region */
 static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
 {
     struct damon_target *t;
     struct damon_region *r;
     unsigned long sz = 0;
 
     damon_for_each_target(t, ctx) {
         damon_for_each_region(r, t)
             sz += r->ar.end - r->ar.start;
     }
 
     if (ctx->min_nr_regions)
         sz /= ctx->min_nr_regions;
     if (sz < DAMON_MIN_REGION)
         sz = DAMON_MIN_REGION;
 
     return sz;
 }
 
 static int kdamond_fn(void *data);
 
 /*
  * __damon_start() - Starts monitoring with given context.
  * @ctx:    monitoring context
  *
  * This function should be called while damon_lock is hold.
  *
  * Return: 0 on success, negative error code otherwise.
  */
 static int __damon_start(struct damon_ctx *ctx)
 {
     int err = -EBUSY;
 
     mutex_lock(&ctx->kdamond_lock);
     if (!ctx->kdamond) {
         err = 0;
         ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
                 nr_running_ctxs);
         if (IS_ERR(ctx->kdamond)) {
             err = PTR_ERR(ctx->kdamond);
             ctx->kdamond = NULL;
         }
     }
     mutex_unlock(&ctx->kdamond_lock);
 
     return err;
 }
 
 /**
  * damon_start() - Starts the monitorings for a given group of contexts.
  * @ctxs:   an array of the pointers for contexts to start monitoring
  * @nr_ctxs:    size of @ctxs
  * @exclusive:  exclusiveness of this contexts group
  *
  * This function starts a group of monitoring threads for a group of monitoring
  * contexts.  One thread per each context is created and run in parallel.  The
  * caller should handle synchronization between the threads by itself.  If
  * @exclusive is true and a group of threads that created by other
  * 'damon_start()' call is currently running, this function does nothing but
  * returns -EBUSY.
  *
  * Return: 0 on success, negative error code otherwise.
  */
 int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive)
 {
     int i;
     int err = 0;
 
     mutex_lock(&damon_lock);
     if ((exclusive && nr_running_ctxs) ||
             (!exclusive && running_exclusive_ctxs)) {
         mutex_unlock(&damon_lock);
         return -EBUSY;
     }
 
     for (i = 0; i < nr_ctxs; i++) {
         err = __damon_start(ctxs[i]);
         if (err)
             break;
         nr_running_ctxs++;
     }
     if (exclusive && nr_running_ctxs)
         running_exclusive_ctxs = true;
     mutex_unlock(&damon_lock);
 
     return err;
 }
 
 /*
  * __damon_stop() - Stops monitoring of a given context.
  * @ctx:    monitoring context
  *
  * Return: 0 on success, negative error code otherwise.
  */
 static int __damon_stop(struct damon_ctx *ctx)
 {
     struct task_struct *tsk;
 
     mutex_lock(&ctx->kdamond_lock);
     tsk = ctx->kdamond;
     if (tsk) {
         get_task_struct(tsk);
         mutex_unlock(&ctx->kdamond_lock);
         kthread_stop(tsk);
         put_task_struct(tsk);
         return 0;
     }
     mutex_unlock(&ctx->kdamond_lock);
 
     return -EPERM;
 }
 
 /**
  * damon_stop() - Stops the monitorings for a given group of contexts.
  * @ctxs:   an array of the pointers for contexts to stop monitoring
  * @nr_ctxs:    size of @ctxs
  *
  * Return: 0 on success, negative error code otherwise.
  */
 int damon_stop(struct damon_ctx **ctxs, int nr_ctxs)
 {
     int i, err = 0;
 
     for (i = 0; i < nr_ctxs; i++) {
         /* nr_running_ctxs is decremented in kdamond_fn */
         err = __damon_stop(ctxs[i]);
         if (err)
             break;
     }
     return err;
 }
 
 /*
  * damon_check_reset_time_interval() - Check if a time interval is elapsed.
  * @baseline:   the time to check whether the interval has elapsed since
  * @interval:   the time interval (microseconds)
  *
  * See whether the given time interval has passed since the given baseline
  * time.  If so, it also updates the baseline to current time for next check.
  *
  * Return:  true if the time interval has passed, or false otherwise.
  */
 static bool damon_check_reset_time_interval(struct timespec64 *baseline,
         unsigned long interval)
 {
     struct timespec64 now;
 
     ktime_get_coarse_ts64(&now);
     if ((timespec64_to_ns(&now) - timespec64_to_ns(baseline)) <
             interval * 1000)
         return false;
     *baseline = now;
     return true;
 }
 
 /*
  * Check whether it is time to flush the aggregated information
  */
 static bool kdamond_aggregate_interval_passed(struct damon_ctx *ctx)
 {
     return damon_check_reset_time_interval(&ctx->last_aggregation,
             ctx->aggr_interval);
 }
 
 /*
  * Reset the aggregated monitoring results ('nr_accesses' of each region).
  */
 static void kdamond_reset_aggregated(struct damon_ctx *c)
 {
     struct damon_target *t;
     unsigned int ti = 0;    /* target's index */
 
     damon_for_each_target(t, c) {
         struct damon_region *r;
 
         damon_for_each_region(r, t) {
             trace_damon_aggregated(t, ti, r, damon_nr_regions(t));
             r->last_nr_accesses = r->nr_accesses;
             r->nr_accesses = 0;
         }
         ti++;
     }
 }
 
 static void damon_split_region_at(struct damon_ctx *ctx,
         struct damon_target *t, struct damon_region *r,
         unsigned long sz_r);
 
 static bool __damos_valid_target(struct damon_region *r, struct damos *s)
 {
     unsigned long sz;
 
     sz = r->ar.end - r->ar.start;
     return s->min_sz_region <= sz && sz <= s->max_sz_region &&
         s->min_nr_accesses <= r->nr_accesses &&
         r->nr_accesses <= s->max_nr_accesses &&
         s->min_age_region <= r->age && r->age <= s->max_age_region;
 }
 
 static bool damos_valid_target(struct damon_ctx *c, struct damon_target *t,
         struct damon_region *r, struct damos *s)
 {
     bool ret = __damos_valid_target(r, s);
 
     if (!ret || !s->quota.esz || !c->ops.get_scheme_score)
         return ret;
 
     return c->ops.get_scheme_score(c, t, r, s) >= s->quota.min_score;
 }
 
 static void damon_do_apply_schemes(struct damon_ctx *c,
                    struct damon_target *t,
                    struct damon_region *r)
 {
     struct damos *s;
 
     damon_for_each_scheme(s, c) {
         struct damos_quota *quota = &s->quota;
         unsigned long sz = r->ar.end - r->ar.start;
         struct timespec64 begin, end;
         unsigned long sz_applied = 0;
 
         if (!s->wmarks.activated)
             continue;
 
         /* Check the quota */
         if (quota->esz && quota->charged_sz >= quota->esz)
             continue;
 
         /* Skip previously charged regions */
         if (quota->charge_target_from) {
             if (t != quota->charge_target_from)
                 continue;
             if (r == damon_last_region(t)) {
                 quota->charge_target_from = NULL;
                 quota->charge_addr_from = 0;
                 continue;
             }
             if (quota->charge_addr_from &&
                     r->ar.end <= quota->charge_addr_from)
                 continue;
 
             if (quota->charge_addr_from && r->ar.start <
                     quota->charge_addr_from) {
                 sz = ALIGN_DOWN(quota->charge_addr_from -
                         r->ar.start, DAMON_MIN_REGION);
                 if (!sz) {
                     if (r->ar.end - r->ar.start <=
                             DAMON_MIN_REGION)
                         continue;
                     sz = DAMON_MIN_REGION;
                 }
                 damon_split_region_at(c, t, r, sz);
                 r = damon_next_region(r);
                 sz = r->ar.end - r->ar.start;
             }
             quota->charge_target_from = NULL;
             quota->charge_addr_from = 0;
         }
 
         if (!damos_valid_target(c, t, r, s))
             continue;
 
         /* Apply the scheme */
         if (c->ops.apply_scheme) {
             if (quota->esz &&
                     quota->charged_sz + sz > quota->esz) {
                 sz = ALIGN_DOWN(quota->esz - quota->charged_sz,
                         DAMON_MIN_REGION);
                 if (!sz)
                     goto update_stat;
                 damon_split_region_at(c, t, r, sz);
             }
             ktime_get_coarse_ts64(&begin);
             sz_applied = c->ops.apply_scheme(c, t, r, s);
             ktime_get_coarse_ts64(&end);
             quota->total_charged_ns += timespec64_to_ns(&end) -
                 timespec64_to_ns(&begin);
             quota->charged_sz += sz;
             if (quota->esz && quota->charged_sz >= quota->esz) {
                 quota->charge_target_from = t;
                 quota->charge_addr_from = r->ar.end + 1;
             }
         }
         if (s->action != DAMOS_STAT)
             r->age = 0;
 
 update_stat:
         s->stat.nr_tried++;
         s->stat.sz_tried += sz;
         if (sz_applied)
             s->stat.nr_applied++;
         s->stat.sz_applied += sz_applied;
     }
 }
 
 /* Shouldn't be called if quota->ms and quota->sz are zero */
 static void damos_set_effective_quota(struct damos_quota *quota)
 {
     unsigned long throughput;
     unsigned long esz;
 
     if (!quota->ms) {
         quota->esz = quota->sz;
         return;
     }
 
     if (quota->total_charged_ns)
         throughput = quota->total_charged_sz * 1000000 /
             quota->total_charged_ns;
     else
         throughput = PAGE_SIZE * 1024;
     esz = throughput * quota->ms;
 
     if (quota->sz && quota->sz < esz)
         esz = quota->sz;
     quota->esz = esz;
 }
 
 static void kdamond_apply_schemes(struct damon_ctx *c)
 {
     struct damon_target *t;
     struct damon_region *r, *next_r;
     struct damos *s;
 
     damon_for_each_scheme(s, c) {
         struct damos_quota *quota = &s->quota;
         unsigned long cumulated_sz;
         unsigned int score, max_score = 0;
 
         if (!s->wmarks.activated)
             continue;
 
         if (!quota->ms && !quota->sz)
             continue;
 
         /* New charge window starts */
         if (time_after_eq(jiffies, quota->charged_from +
                     msecs_to_jiffies(
                         quota->reset_interval))) {
             if (quota->esz && quota->charged_sz >= quota->esz)
                 s->stat.qt_exceeds++;
             quota->total_charged_sz += quota->charged_sz;
             quota->charged_from = jiffies;
             quota->charged_sz = 0;
             damos_set_effective_quota(quota);
         }
 
         if (!c->ops.get_scheme_score)
             continue;
 
         /* Fill up the score histogram */
         memset(quota->histogram, 0, sizeof(quota->histogram));
         damon_for_each_target(t, c) {
             damon_for_each_region(r, t) {
                 if (!__damos_valid_target(r, s))
                     continue;
                 score = c->ops.get_scheme_score(
                         c, t, r, s);
                 quota->histogram[score] +=
                     r->ar.end - r->ar.start;
                 if (score > max_score)
                     max_score = score;
             }
         }
 
         /* Set the min score limit */
         for (cumulated_sz = 0, score = max_score; ; score--) {
             cumulated_sz += quota->histogram[score];
             if (cumulated_sz >= quota->esz || !score)
                 break;
         }
         quota->min_score = score;
     }
 
     damon_for_each_target(t, c) {
         damon_for_each_region_safe(r, next_r, t)
             damon_do_apply_schemes(c, t, r);
     }
 }
 
 static inline unsigned long sz_damon_region(struct damon_region *r)
 {
     return r->ar.end - r->ar.start;
 }
 
 /*
  * Merge two adjacent regions into one region
  */
 static void damon_merge_two_regions(struct damon_target *t,
         struct damon_region *l, struct damon_region *r)
 {
     unsigned long sz_l = sz_damon_region(l), sz_r = sz_damon_region(r);
 
     l->nr_accesses = (l->nr_accesses * sz_l + r->nr_accesses * sz_r) /
             (sz_l + sz_r);
     l->age = (l->age * sz_l + r->age * sz_r) / (sz_l + sz_r);
     l->ar.end = r->ar.end;
     damon_destroy_region(r, t);
 }
 
 /*
  * Merge adjacent regions having similar access frequencies
  *
  * t        target affected by this merge operation
  * thres    '->nr_accesses' diff threshold for the merge
  * sz_limit size upper limit of each region
  */
 static void damon_merge_regions_of(struct damon_target *t, unsigned int thres,
                    unsigned long sz_limit)
 {
     struct damon_region *r, *prev = NULL, *next;
 
     damon_for_each_region_safe(r, next, t) {
         if (abs(r->nr_accesses - r->last_nr_accesses) > thres)
             r->age = 0;
         else
             r->age++;
 
         if (prev && prev->ar.end == r->ar.start &&
             abs(prev->nr_accesses - r->nr_accesses) <= thres &&
             sz_damon_region(prev) + sz_damon_region(r) <= sz_limit)
             damon_merge_two_regions(t, prev, r);
         else
             prev = r;
     }
 }
 
 /*
  * Merge adjacent regions having similar access frequencies
  *
  * threshold    '->nr_accesses' diff threshold for the merge
  * sz_limit size upper limit of each region
  *
  * This function merges monitoring target regions which are adjacent and their
  * access frequencies are similar.  This is for minimizing the monitoring
  * overhead under the dynamically changeable access pattern.  If a merge was
  * unnecessarily made, later 'kdamond_split_regions()' will revert it.
  */
 static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold,
                   unsigned long sz_limit)
 {
     struct damon_target *t;
 
     damon_for_each_target(t, c)
         damon_merge_regions_of(t, threshold, sz_limit);
 }
 
 /*
  * Split a region in two
  *
  * r        the region to be split
  * sz_r     size of the first sub-region that will be made
  */
 static void damon_split_region_at(struct damon_ctx *ctx,
         struct damon_target *t, struct damon_region *r,
         unsigned long sz_r)
 {
     struct damon_region *new;
 
     new = damon_new_region(r->ar.start + sz_r, r->ar.end);
     if (!new)
         return;
 
     r->ar.end = new->ar.start;
 
     new->age = r->age;
     new->last_nr_accesses = r->last_nr_accesses;
 
     damon_insert_region(new, r, damon_next_region(r), t);
 }
 
 /* Split every region in the given target into 'nr_subs' regions */
 static void damon_split_regions_of(struct damon_ctx *ctx,
                      struct damon_target *t, int nr_subs)
 {
     struct damon_region *r, *next;
     unsigned long sz_region, sz_sub = 0;
     int i;
 
     damon_for_each_region_safe(r, next, t) {
         sz_region = r->ar.end - r->ar.start;
 
         for (i = 0; i < nr_subs - 1 &&
                 sz_region > 2 * DAMON_MIN_REGION; i++) {
             /*
              * Randomly select size of left sub-region to be at
              * least 10 percent and at most 90% of original region
              */
             sz_sub = ALIGN_DOWN(damon_rand(1, 10) *
                     sz_region / 10, DAMON_MIN_REGION);
             /* Do not allow blank region */
             if (sz_sub == 0 || sz_sub >= sz_region)
                 continue;
 
             damon_split_region_at(ctx, t, r, sz_sub);
             sz_region = sz_sub;
         }
     }
 }
 
 /*
  * Split every target region into randomly-sized small regions
  *
  * This function splits every target region into random-sized small regions if
  * current total number of the regions is equal or smaller than half of the
  * user-specified maximum number of regions.  This is for maximizing the
  * monitoring accuracy under the dynamically changeable access patterns.  If a
  * split was unnecessarily made, later 'kdamond_merge_regions()' will revert
  * it.
  */
 static void kdamond_split_regions(struct damon_ctx *ctx)
 {
     struct damon_target *t;
     unsigned int nr_regions = 0;
     static unsigned int last_nr_regions;
     int nr_subregions = 2;
 
     damon_for_each_target(t, ctx)
         nr_regions += damon_nr_regions(t);
 
     if (nr_regions > ctx->max_nr_regions / 2)
         return;
 
     /* Maybe the middle of the region has different access frequency */
     if (last_nr_regions == nr_regions &&
             nr_regions < ctx->max_nr_regions / 3)
         nr_subregions = 3;
 
     damon_for_each_target(t, ctx)
         damon_split_regions_of(ctx, t, nr_subregions);
 
     last_nr_regions = nr_regions;
 }
 
 /*
  * Check whether it is time to check and apply the operations-related data
  * structures.
  *
  * Returns true if it is.
  */
 static bool kdamond_need_update_operations(struct damon_ctx *ctx)
 {
     return damon_check_reset_time_interval(&ctx->last_ops_update,
             ctx->ops_update_interval);
 }
 
 /*
  * Check whether current monitoring should be stopped
  *
  * The monitoring is stopped when either the user requested to stop, or all
  * monitoring targets are invalid.
  *
  * Returns true if need to stop current monitoring.
  */
 static bool kdamond_need_stop(struct damon_ctx *ctx)
 {
     struct damon_target *t;
 
     if (kthread_should_stop())
         return true;
 
     if (!ctx->ops.target_valid)
         return false;
 
     damon_for_each_target(t, ctx) {
         if (ctx->ops.target_valid(t))
             return false;
     }
 
     return true;
 }
 
 static unsigned long damos_wmark_metric_value(enum damos_wmark_metric metric)
 {
     struct sysinfo i;
 
     switch (metric) {
     case DAMOS_WMARK_FREE_MEM_RATE:
         si_meminfo(&i);
         return i.freeram * 1000 / i.totalram;
     default:
         break;
     }
     return -EINVAL;
 }
 
 /*
  * Returns zero if the scheme is active.  Else, returns time to wait for next
  * watermark check in micro-seconds.
  */
 static unsigned long damos_wmark_wait_us(struct damos *scheme)
 {
     unsigned long metric;
 
     if (scheme->wmarks.metric == DAMOS_WMARK_NONE)
         return 0;
 
     metric = damos_wmark_metric_value(scheme->wmarks.metric);
     /* higher than high watermark or lower than low watermark */
     if (metric > scheme->wmarks.high || scheme->wmarks.low > metric) {
         if (scheme->wmarks.activated)
             pr_debug("deactivate a scheme (%d) for %s wmark\n",
                     scheme->action,
                     metric > scheme->wmarks.high ?
                     "high" : "low");
         scheme->wmarks.activated = false;
         return scheme->wmarks.interval;
     }
 
     /* inactive and higher than middle watermark */
     if ((scheme->wmarks.high >= metric && metric >= scheme->wmarks.mid) &&
             !scheme->wmarks.activated)
         return scheme->wmarks.interval;
 
     if (!scheme->wmarks.activated)
         pr_debug("activate a scheme (%d)\n", scheme->action);
     scheme->wmarks.activated = true;
     return 0;
 }
 
 static void kdamond_usleep(unsigned long usecs)
 {
     /* See Documentation/timers/timers-howto.rst for the thresholds */
     if (usecs > 20 * USEC_PER_MSEC)
         schedule_timeout_idle(usecs_to_jiffies(usecs));
     else
         usleep_idle_range(usecs, usecs + 1);
 }
 
 /* Returns negative error code if it's not activated but should return */
 static int kdamond_wait_activation(struct damon_ctx *ctx)
 {
     struct damos *s;
     unsigned long wait_time;
     unsigned long min_wait_time = 0;
     bool init_wait_time = false;
 
     while (!kdamond_need_stop(ctx)) {
         damon_for_each_scheme(s, ctx) {
             wait_time = damos_wmark_wait_us(s);
             if (!init_wait_time || wait_time < min_wait_time) {
                 init_wait_time = true;
                 min_wait_time = wait_time;
             }
         }
         if (!min_wait_time)
             return 0;
 
         kdamond_usleep(min_wait_time);
 
         if (ctx->callback.after_wmarks_check &&
                 ctx->callback.after_wmarks_check(ctx))
             break;
     }
     return -EBUSY;
 }
 
 /*
  * The monitoring daemon that runs as a kernel thread
  */
 static int kdamond_fn(void *data)
 {
     struct damon_ctx *ctx = data;
     struct damon_target *t;
     struct damon_region *r, *next;
     unsigned int max_nr_accesses = 0;
     unsigned long sz_limit = 0;
     bool done = false;
 
     pr_debug("kdamond (%d) starts\n", current->pid);
 
     if (ctx->ops.init)
         ctx->ops.init(ctx);
     if (ctx->callback.before_start && ctx->callback.before_start(ctx))
         done = true;
 
     sz_limit = damon_region_sz_limit(ctx);
 
     while (!kdamond_need_stop(ctx) && !done) {
         if (kdamond_wait_activation(ctx)) {
             done = true;
             continue;
         }
 
         if (ctx->ops.prepare_access_checks)
             ctx->ops.prepare_access_checks(ctx);
         if (ctx->callback.after_sampling &&
                 ctx->callback.after_sampling(ctx)) {
             done = true;
             continue;
         }
 
         kdamond_usleep(ctx->sample_interval);
 
         if (ctx->ops.check_accesses)
             max_nr_accesses = ctx->ops.check_accesses(ctx);
 
         if (kdamond_aggregate_interval_passed(ctx)) {
             kdamond_merge_regions(ctx,
                     max_nr_accesses / 10,
                     sz_limit);
             if (ctx->callback.after_aggregation &&
                     ctx->callback.after_aggregation(ctx)) {
                 done = true;
                 continue;
             }
             kdamond_apply_schemes(ctx);
             kdamond_reset_aggregated(ctx);
             kdamond_split_regions(ctx);
             if (ctx->ops.reset_aggregated)
                 ctx->ops.reset_aggregated(ctx);
         }
 
         if (kdamond_need_update_operations(ctx)) {
             if (ctx->ops.update)
                 ctx->ops.update(ctx);
             sz_limit = damon_region_sz_limit(ctx);
         }
     }
     damon_for_each_target(t, ctx) {
         damon_for_each_region_safe(r, next, t)
             damon_destroy_region(r, t);
     }
 
     if (ctx->callback.before_terminate)
         ctx->callback.before_terminate(ctx);
     if (ctx->ops.cleanup)
         ctx->ops.cleanup(ctx);
 
     pr_debug("kdamond (%d) finishes\n", current->pid);
     mutex_lock(&ctx->kdamond_lock);
     ctx->kdamond = NULL;
     mutex_unlock(&ctx->kdamond_lock);
 
     mutex_lock(&damon_lock);
     nr_running_ctxs--;
     if (!nr_running_ctxs && running_exclusive_ctxs)
         running_exclusive_ctxs = false;
     mutex_unlock(&damon_lock);
 
     return 0;
 }
 
 #include "core-test.h"

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