Merge tag 'loongarch-kvm-6.8' of git://git.kernel.org/pub/scm/linux/kernel/git/chenhu...

[thirdparty/kernel/stable.git] / mm / damon / core.c

// 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];

static struct kmem_cache *damon_region_cache __ro_after_init;

/* 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 = kmem_cache_alloc(damon_region_cache, GFP_KERNEL);
        if (!region)
                return NULL;

        region->ar.start = start;
        region->ar.end = end;
        region->nr_accesses = 0;
        region->nr_accesses_bp = 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)
{
        kmem_cache_free(damon_region_cache, 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);
}

/*
 * Fill holes in regions with new regions.
 */
static int damon_fill_regions_holes(struct damon_region *first,
                struct damon_region *last, struct damon_target *t)
{
        struct damon_region *r = first;

        damon_for_each_region_from(r, t) {
                struct damon_region *next, *newr;

                if (r == last)
                        break;
                next = damon_next_region(r);
                if (r->ar.end != next->ar.start) {
                        newr = damon_new_region(r->ar.end, next->ar.start);
                        if (!newr)
                                return -ENOMEM;
                        damon_insert_region(newr, r, next, t);
                }
        }
        return 0;
}

/*
 * 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;
        int err;

        /* 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);
        }

        r = damon_first_region(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_from(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);

                        /* fill possible holes in the range */
                        err = damon_fill_regions_holes(first, last, t);
                        if (err)
                                return err;
                }
        }
        return 0;
}

struct damos_filter *damos_new_filter(enum damos_filter_type type,
                bool matching)
{
        struct damos_filter *filter;

        filter = kmalloc(sizeof(*filter), GFP_KERNEL);
        if (!filter)
                return NULL;
        filter->type = type;
        filter->matching = matching;
        INIT_LIST_HEAD(&filter->list);
        return filter;
}

void damos_add_filter(struct damos *s, struct damos_filter *f)
{
        list_add_tail(&f->list, &s->filters);
}

static void damos_del_filter(struct damos_filter *f)
{
        list_del(&f->list);
}

static void damos_free_filter(struct damos_filter *f)
{
        kfree(f);
}

void damos_destroy_filter(struct damos_filter *f)
{
        damos_del_filter(f);
        damos_free_filter(f);
}

/* initialize private fields of damos_quota and return the pointer */
static struct damos_quota *damos_quota_init_priv(struct damos_quota *quota)
{
        quota->total_charged_sz = 0;
        quota->total_charged_ns = 0;
        quota->esz = 0;
        quota->charged_sz = 0;
        quota->charged_from = 0;
        quota->charge_target_from = NULL;
        quota->charge_addr_from = 0;
        return quota;
}

struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
                        enum damos_action action,
                        unsigned long apply_interval_us,
                        struct damos_quota *quota,
                        struct damos_watermarks *wmarks)
{
        struct damos *scheme;

        scheme = kmalloc(sizeof(*scheme), GFP_KERNEL);
        if (!scheme)
                return NULL;
        scheme->pattern = *pattern;
        scheme->action = action;
        scheme->apply_interval_us = apply_interval_us;
        /*
         * next_apply_sis will be set when kdamond starts.  While kdamond is
         * running, it will also updated when it is added to the DAMON context,
         * or damon_attrs are updated.
         */
        scheme->next_apply_sis = 0;
        INIT_LIST_HEAD(&scheme->filters);
        scheme->stat = (struct damos_stat){};
        INIT_LIST_HEAD(&scheme->list);

        scheme->quota = *(damos_quota_init_priv(quota));

        scheme->wmarks = *wmarks;
        scheme->wmarks.activated = true;

        return scheme;
}

static void damos_set_next_apply_sis(struct damos *s, struct damon_ctx *ctx)
{
        unsigned long sample_interval = ctx->attrs.sample_interval ?
                ctx->attrs.sample_interval : 1;
        unsigned long apply_interval = s->apply_interval_us ?
                s->apply_interval_us : ctx->attrs.aggr_interval;

        s->next_apply_sis = ctx->passed_sample_intervals +
                apply_interval / sample_interval;
}

void damon_add_scheme(struct damon_ctx *ctx, struct damos *s)
{
        list_add_tail(&s->list, &ctx->schemes);
        damos_set_next_apply_sis(s, ctx);
}

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)
{
        struct damos_filter *f, *next;

        damos_for_each_filter_safe(f, next, s)
                damos_destroy_filter(f);
        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);
        INIT_LIST_HEAD(&t->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;

        init_completion(&ctx->kdamond_started);

        ctx->attrs.sample_interval = 5 * 1000;
        ctx->attrs.aggr_interval = 100 * 1000;
        ctx->attrs.ops_update_interval = 60 * 1000 * 1000;

        ctx->passed_sample_intervals = 0;
        /* These will be set from kdamond_init_intervals_sis() */
        ctx->next_aggregation_sis = 0;
        ctx->next_ops_update_sis = 0;

        mutex_init(&ctx->kdamond_lock);

        ctx->attrs.min_nr_regions = 10;
        ctx->attrs.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);
}

static unsigned int damon_age_for_new_attrs(unsigned int age,
                struct damon_attrs *old_attrs, struct damon_attrs *new_attrs)
{
        return age * old_attrs->aggr_interval / new_attrs->aggr_interval;
}

/* convert access ratio in bp (per 10,000) to nr_accesses */
static unsigned int damon_accesses_bp_to_nr_accesses(
                unsigned int accesses_bp, struct damon_attrs *attrs)
{
        return accesses_bp * damon_max_nr_accesses(attrs) / 10000;
}

/* convert nr_accesses to access ratio in bp (per 10,000) */
static unsigned int damon_nr_accesses_to_accesses_bp(
                unsigned int nr_accesses, struct damon_attrs *attrs)
{
        return nr_accesses * 10000 / damon_max_nr_accesses(attrs);
}

static unsigned int damon_nr_accesses_for_new_attrs(unsigned int nr_accesses,
                struct damon_attrs *old_attrs, struct damon_attrs *new_attrs)
{
        return damon_accesses_bp_to_nr_accesses(
                        damon_nr_accesses_to_accesses_bp(
                                nr_accesses, old_attrs),
                        new_attrs);
}

static void damon_update_monitoring_result(struct damon_region *r,
                struct damon_attrs *old_attrs, struct damon_attrs *new_attrs)
{
        r->nr_accesses = damon_nr_accesses_for_new_attrs(r->nr_accesses,
                        old_attrs, new_attrs);
        r->nr_accesses_bp = r->nr_accesses * 10000;
        r->age = damon_age_for_new_attrs(r->age, old_attrs, new_attrs);
}

/*
 * region->nr_accesses is the number of sampling intervals in the last
 * aggregation interval that access to the region has found, and region->age is
 * the number of aggregation intervals that its access pattern has maintained.
 * For the reason, the real meaning of the two fields depend on current
 * sampling interval and aggregation interval.  This function updates
 * ->nr_accesses and ->age of given damon_ctx's regions for new damon_attrs.
 */
static void damon_update_monitoring_results(struct damon_ctx *ctx,
                struct damon_attrs *new_attrs)
{
        struct damon_attrs *old_attrs = &ctx->attrs;
        struct damon_target *t;
        struct damon_region *r;

        /* if any interval is zero, simply forgive conversion */
        if (!old_attrs->sample_interval || !old_attrs->aggr_interval ||
                        !new_attrs->sample_interval ||
                        !new_attrs->aggr_interval)
                return;

        damon_for_each_target(t, ctx)
                damon_for_each_region(r, t)
                        damon_update_monitoring_result(
                                        r, old_attrs, new_attrs);
}

/**
 * damon_set_attrs() - Set attributes for the monitoring.
 * @ctx:                monitoring context
 * @attrs:              monitoring attributes
 *
 * This function should be called while the kdamond is not running, or an
 * access check results aggregation is not ongoing (e.g., from
 * &struct damon_callback->after_aggregation or
 * &struct damon_callback->after_wmarks_check callbacks).
 *
 * Every time interval is in micro-seconds.
 *
 * Return: 0 on success, negative error code otherwise.
 */
int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs)
{
        unsigned long sample_interval = attrs->sample_interval ?
                attrs->sample_interval : 1;
        struct damos *s;

        if (attrs->min_nr_regions < 3)
                return -EINVAL;
        if (attrs->min_nr_regions > attrs->max_nr_regions)
                return -EINVAL;
        if (attrs->sample_interval > attrs->aggr_interval)
                return -EINVAL;

        ctx->next_aggregation_sis = ctx->passed_sample_intervals +
                attrs->aggr_interval / sample_interval;
        ctx->next_ops_update_sis = ctx->passed_sample_intervals +
                attrs->ops_update_interval / sample_interval;

        damon_update_monitoring_results(ctx, attrs);
        ctx->attrs = *attrs;

        damon_for_each_scheme(s, ctx)
                damos_set_next_apply_sis(s, ctx);

        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.
 */
void 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]);
}

/**
 * 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 += damon_sz_region(r);
        }

        if (ctx->attrs.min_nr_regions)
                sz /= ctx->attrs.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;
                reinit_completion(&ctx->kdamond_started);
                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;
                } else {
                        wait_for_completion(&ctx->kdamond_started);
                }
        }
        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_put(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;
}

/*
 * 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(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_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;
        unsigned int nr_accesses = r->nr_accesses_bp / 10000;

        sz = damon_sz_region(r);
        return s->pattern.min_sz_region <= sz &&
                sz <= s->pattern.max_sz_region &&
                s->pattern.min_nr_accesses <= nr_accesses &&
                nr_accesses <= s->pattern.max_nr_accesses &&
                s->pattern.min_age_region <= r->age &&
                r->age <= s->pattern.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;
}

/*
 * damos_skip_charged_region() - Check if the given region or starting part of
 * it is already charged for the DAMOS quota.
 * @t:  The target of the region.
 * @rp: The pointer to the region.
 * @s:  The scheme to be applied.
 *
 * If a quota of a scheme has exceeded in a quota charge window, the scheme's
 * action would applied to only a part of the target access pattern fulfilling
 * regions.  To avoid applying the scheme action to only already applied
 * regions, DAMON skips applying the scheme action to the regions that charged
 * in the previous charge window.
 *
 * This function checks if a given region should be skipped or not for the
 * reason.  If only the starting part of the region has previously charged,
 * this function splits the region into two so that the second one covers the
 * area that not charged in the previous charge widnow and saves the second
 * region in *rp and returns false, so that the caller can apply DAMON action
 * to the second one.
 *
 * Return: true if the region should be entirely skipped, false otherwise.
 */
static bool damos_skip_charged_region(struct damon_target *t,
                struct damon_region **rp, struct damos *s)
{
        struct damon_region *r = *rp;
        struct damos_quota *quota = &s->quota;
        unsigned long sz_to_skip;

        /* Skip previously charged regions */
        if (quota->charge_target_from) {
                if (t != quota->charge_target_from)
                        return true;
                if (r == damon_last_region(t)) {
                        quota->charge_target_from = NULL;
                        quota->charge_addr_from = 0;
                        return true;
                }
                if (quota->charge_addr_from &&
                                r->ar.end <= quota->charge_addr_from)
                        return true;

                if (quota->charge_addr_from && r->ar.start <
                                quota->charge_addr_from) {
                        sz_to_skip = ALIGN_DOWN(quota->charge_addr_from -
                                        r->ar.start, DAMON_MIN_REGION);
                        if (!sz_to_skip) {
                                if (damon_sz_region(r) <= DAMON_MIN_REGION)
                                        return true;
                                sz_to_skip = DAMON_MIN_REGION;
                        }
                        damon_split_region_at(t, r, sz_to_skip);
                        r = damon_next_region(r);
                        *rp = r;
                }
                quota->charge_target_from = NULL;
                quota->charge_addr_from = 0;
        }
        return false;
}

static void damos_update_stat(struct damos *s,
                unsigned long sz_tried, unsigned long sz_applied)
{
        s->stat.nr_tried++;
        s->stat.sz_tried += sz_tried;
        if (sz_applied)
                s->stat.nr_applied++;
        s->stat.sz_applied += sz_applied;
}

static bool __damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
                struct damon_region *r, struct damos_filter *filter)
{
        bool matched = false;
        struct damon_target *ti;
        int target_idx = 0;
        unsigned long start, end;

        switch (filter->type) {
        case DAMOS_FILTER_TYPE_TARGET:
                damon_for_each_target(ti, ctx) {
                        if (ti == t)
                                break;
                        target_idx++;
                }
                matched = target_idx == filter->target_idx;
                break;
        case DAMOS_FILTER_TYPE_ADDR:
                start = ALIGN_DOWN(filter->addr_range.start, DAMON_MIN_REGION);
                end = ALIGN_DOWN(filter->addr_range.end, DAMON_MIN_REGION);

                /* inside the range */
                if (start <= r->ar.start && r->ar.end <= end) {
                        matched = true;
                        break;
                }
                /* outside of the range */
                if (r->ar.end <= start || end <= r->ar.start) {
                        matched = false;
                        break;
                }
                /* start before the range and overlap */
                if (r->ar.start < start) {
                        damon_split_region_at(t, r, start - r->ar.start);
                        matched = false;
                        break;
                }
                /* start inside the range */
                damon_split_region_at(t, r, end - r->ar.start);
                matched = true;
                break;
        default:
                return false;
        }

        return matched == filter->matching;
}

static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
                struct damon_region *r, struct damos *s)
{
        struct damos_filter *filter;

        damos_for_each_filter(filter, s) {
                if (__damos_filter_out(ctx, t, r, filter))
                        return true;
        }
        return false;
}

static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
                struct damon_region *r, struct damos *s)
{
        struct damos_quota *quota = &s->quota;
        unsigned long sz = damon_sz_region(r);
        struct timespec64 begin, end;
        unsigned long sz_applied = 0;
        int err = 0;
        /*
         * We plan to support multiple context per kdamond, as DAMON sysfs
         * implies with 'nr_contexts' file.  Nevertheless, only single context
         * per kdamond is supported for now.  So, we can simply use '0' context
         * index here.
         */
        unsigned int cidx = 0;
        struct damos *siter;            /* schemes iterator */
        unsigned int sidx = 0;
        struct damon_target *titer;     /* targets iterator */
        unsigned int tidx = 0;
        bool do_trace = false;

        /* get indices for trace_damos_before_apply() */
        if (trace_damos_before_apply_enabled()) {
                damon_for_each_scheme(siter, c) {
                        if (siter == s)
                                break;
                        sidx++;
                }
                damon_for_each_target(titer, c) {
                        if (titer == t)
                                break;
                        tidx++;
                }
                do_trace = true;
        }

        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(t, r, sz);
                }
                if (damos_filter_out(c, t, r, s))
                        return;
                ktime_get_coarse_ts64(&begin);
                if (c->callback.before_damos_apply)
                        err = c->callback.before_damos_apply(c, t, r, s);
                if (!err) {
                        trace_damos_before_apply(cidx, sidx, tidx, r,
                                        damon_nr_regions(t), do_trace);
                        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:
        damos_update_stat(s, sz, sz_applied);
}

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;

                if (!s->wmarks.activated)
                        continue;

                /* Check the quota */
                if (quota->esz && quota->charged_sz >= quota->esz)
                        continue;

                if (damos_skip_charged_region(t, &r, s))
                        continue;

                if (!damos_valid_target(c, t, r, s))
                        continue;

                damos_apply_scheme(c, t, r, s);
        }
}

/* 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 damos_adjust_quota(struct damon_ctx *c, struct damos *s)
{
        struct damos_quota *quota = &s->quota;
        struct damon_target *t;
        struct damon_region *r;
        unsigned long cumulated_sz;
        unsigned int score, max_score = 0;

        if (!quota->ms && !quota->sz)
                return;

        /* 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)
                return;

        /* 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] += damon_sz_region(r);
                        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;
}

static void kdamond_apply_schemes(struct damon_ctx *c)
{
        struct damon_target *t;
        struct damon_region *r, *next_r;
        struct damos *s;
        unsigned long sample_interval = c->attrs.sample_interval ?
                c->attrs.sample_interval : 1;
        bool has_schemes_to_apply = false;

        damon_for_each_scheme(s, c) {
                if (c->passed_sample_intervals != s->next_apply_sis)
                        continue;

                s->next_apply_sis +=
                        (s->apply_interval_us ? s->apply_interval_us :
                         c->attrs.aggr_interval) / sample_interval;

                if (!s->wmarks.activated)
                        continue;

                has_schemes_to_apply = true;

                damos_adjust_quota(c, s);
        }

        if (!has_schemes_to_apply)
                return;

        damon_for_each_target(t, c) {
                damon_for_each_region_safe(r, next_r, t)
                        damon_do_apply_schemes(c, t, r);
        }
}

/*
 * 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 = damon_sz_region(l), sz_r = damon_sz_region(r);

        l->nr_accesses = (l->nr_accesses * sz_l + r->nr_accesses * sz_r) /
                        (sz_l + sz_r);
        l->nr_accesses_bp = l->nr_accesses * 10000;
        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 &&
                    damon_sz_region(prev) + damon_sz_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_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;
        new->nr_accesses_bp = r->nr_accesses_bp;
        new->nr_accesses = r->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_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 = damon_sz_region(r);

                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(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->attrs.max_nr_regions / 2)
                return;

        /* Maybe the middle of the region has different access frequency */
        if (last_nr_regions == nr_regions &&
                        nr_regions < ctx->attrs.max_nr_regions / 3)
                nr_subregions = 3;

        damon_for_each_target(t, ctx)
                damon_split_regions_of(t, nr_subregions);

        last_nr_regions = nr_regions;
}

/*
 * 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)
{
        switch (metric) {
        case DAMOS_WMARK_FREE_MEM_RATE:
                return global_zone_page_state(NR_FREE_PAGES) * 1000 /
                       totalram_pages();
        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;
}

static void kdamond_init_intervals_sis(struct damon_ctx *ctx)
{
        unsigned long sample_interval = ctx->attrs.sample_interval ?
                ctx->attrs.sample_interval : 1;
        unsigned long apply_interval;
        struct damos *scheme;

        ctx->passed_sample_intervals = 0;
        ctx->next_aggregation_sis = ctx->attrs.aggr_interval / sample_interval;
        ctx->next_ops_update_sis = ctx->attrs.ops_update_interval /
                sample_interval;

        damon_for_each_scheme(scheme, ctx) {
                apply_interval = scheme->apply_interval_us ?
                        scheme->apply_interval_us : ctx->attrs.aggr_interval;
                scheme->next_apply_sis = apply_interval / sample_interval;
        }
}

/*
 * 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;

        pr_debug("kdamond (%d) starts\n", current->pid);

        complete(&ctx->kdamond_started);
        kdamond_init_intervals_sis(ctx);

        if (ctx->ops.init)
                ctx->ops.init(ctx);
        if (ctx->callback.before_start && ctx->callback.before_start(ctx))
                goto done;

        sz_limit = damon_region_sz_limit(ctx);

        while (!kdamond_need_stop(ctx)) {
                /*
                 * ctx->attrs and ctx->next_{aggregation,ops_update}_sis could
                 * be changed from after_wmarks_check() or after_aggregation()
                 * callbacks.  Read the values here, and use those for this
                 * iteration.  That is, damon_set_attrs() updated new values
                 * are respected from next iteration.
                 */
                unsigned long next_aggregation_sis = ctx->next_aggregation_sis;
                unsigned long next_ops_update_sis = ctx->next_ops_update_sis;
                unsigned long sample_interval = ctx->attrs.sample_interval;

                if (kdamond_wait_activation(ctx))
                        break;

                if (ctx->ops.prepare_access_checks)
                        ctx->ops.prepare_access_checks(ctx);
                if (ctx->callback.after_sampling &&
                                ctx->callback.after_sampling(ctx))
                        break;

                kdamond_usleep(sample_interval);
                ctx->passed_sample_intervals++;

                if (ctx->ops.check_accesses)
                        max_nr_accesses = ctx->ops.check_accesses(ctx);

                if (ctx->passed_sample_intervals == next_aggregation_sis) {
                        kdamond_merge_regions(ctx,
                                        max_nr_accesses / 10,
                                        sz_limit);
                        if (ctx->callback.after_aggregation &&
                                        ctx->callback.after_aggregation(ctx))
                                break;
                }

                /*
                 * do kdamond_apply_schemes() after kdamond_merge_regions() if
                 * possible, to reduce overhead
                 */
                if (!list_empty(&ctx->schemes))
                        kdamond_apply_schemes(ctx);

                sample_interval = ctx->attrs.sample_interval ?
                        ctx->attrs.sample_interval : 1;
                if (ctx->passed_sample_intervals == next_aggregation_sis) {
                        ctx->next_aggregation_sis = next_aggregation_sis +
                                ctx->attrs.aggr_interval / sample_interval;

                        kdamond_reset_aggregated(ctx);
                        kdamond_split_regions(ctx);
                        if (ctx->ops.reset_aggregated)
                                ctx->ops.reset_aggregated(ctx);
                }

                if (ctx->passed_sample_intervals == next_ops_update_sis) {
                        ctx->next_ops_update_sis = next_ops_update_sis +
                                ctx->attrs.ops_update_interval /
                                sample_interval;
                        if (ctx->ops.update)
                                ctx->ops.update(ctx);
                        sz_limit = damon_region_sz_limit(ctx);
                }
        }
done:
        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;
}

/*
 * struct damon_system_ram_region - System RAM resource address region of
 *                                  [@start, @end).
 * @start:      Start address of the region (inclusive).
 * @end:        End address of the region (exclusive).
 */
struct damon_system_ram_region {
        unsigned long start;
        unsigned long end;
};

static int walk_system_ram(struct resource *res, void *arg)
{
        struct damon_system_ram_region *a = arg;

        if (a->end - a->start < resource_size(res)) {
                a->start = res->start;
                a->end = res->end;
        }
        return 0;
}

/*
 * Find biggest 'System RAM' resource and store its start and end address in
 * @start and @end, respectively.  If no System RAM is found, returns false.
 */
static bool damon_find_biggest_system_ram(unsigned long *start,
                                                unsigned long *end)

{
        struct damon_system_ram_region arg = {};

        walk_system_ram_res(0, ULONG_MAX, &arg, walk_system_ram);
        if (arg.end <= arg.start)
                return false;

        *start = arg.start;
        *end = arg.end;
        return true;
}

/**
 * damon_set_region_biggest_system_ram_default() - Set the region of the given
 * monitoring target as requested, or biggest 'System RAM'.
 * @t:          The monitoring target to set the region.
 * @start:      The pointer to the start address of the region.
 * @end:        The pointer to the end address of the region.
 *
 * This function sets the region of @t as requested by @start and @end.  If the
 * values of @start and @end are zero, however, this function finds the biggest
 * 'System RAM' resource and sets the region to cover the resource.  In the
 * latter case, this function saves the start and end addresses of the resource
 * in @start and @end, respectively.
 *
 * Return: 0 on success, negative error code otherwise.
 */
int damon_set_region_biggest_system_ram_default(struct damon_target *t,
                        unsigned long *start, unsigned long *end)
{
        struct damon_addr_range addr_range;

        if (*start > *end)
                return -EINVAL;

        if (!*start && !*end &&
                !damon_find_biggest_system_ram(start, end))
                return -EINVAL;

        addr_range.start = *start;
        addr_range.end = *end;
        return damon_set_regions(t, &addr_range, 1);
}

/*
 * damon_moving_sum() - Calculate an inferred moving sum value.
 * @mvsum:      Inferred sum of the last @len_window values.
 * @nomvsum:    Non-moving sum of the last discrete @len_window window values.
 * @len_window: The number of last values to take care of.
 * @new_value:  New value that will be added to the pseudo moving sum.
 *
 * Moving sum (moving average * window size) is good for handling noise, but
 * the cost of keeping past values can be high for arbitrary window size.  This
 * function implements a lightweight pseudo moving sum function that doesn't
 * keep the past window values.
 *
 * It simply assumes there was no noise in the past, and get the no-noise
 * assumed past value to drop from @nomvsum and @len_window.  @nomvsum is a
 * non-moving sum of the last window.  For example, if @len_window is 10 and we
 * have 25 values, @nomvsum is the sum of the 11th to 20th values of the 25
 * values.  Hence, this function simply drops @nomvsum / @len_window from
 * given @mvsum and add @new_value.
 *
 * For example, if @len_window is 10 and @nomvsum is 50, the last 10 values for
 * the last window could be vary, e.g., 0, 10, 0, 10, 0, 10, 0, 0, 0, 20.  For
 * calculating next moving sum with a new value, we should drop 0 from 50 and
 * add the new value.  However, this function assumes it got value 5 for each
 * of the last ten times.  Based on the assumption, when the next value is
 * measured, it drops the assumed past value, 5 from the current sum, and add
 * the new value to get the updated pseduo-moving average.
 *
 * This means the value could have errors, but the errors will be disappeared
 * for every @len_window aligned calls.  For example, if @len_window is 10, the
 * pseudo moving sum with 11th value to 19th value would have an error.  But
 * the sum with 20th value will not have the error.
 *
 * Return: Pseudo-moving average after getting the @new_value.
 */
static unsigned int damon_moving_sum(unsigned int mvsum, unsigned int nomvsum,
                unsigned int len_window, unsigned int new_value)
{
        return mvsum - nomvsum / len_window + new_value;
}

/**
 * damon_update_region_access_rate() - Update the access rate of a region.
 * @r:          The DAMON region to update for its access check result.
 * @accessed:   Whether the region has accessed during last sampling interval.
 * @attrs:      The damon_attrs of the DAMON context.
 *
 * Update the access rate of a region with the region's last sampling interval
 * access check result.
 *
 * Usually this will be called by &damon_operations->check_accesses callback.
 */
void damon_update_region_access_rate(struct damon_region *r, bool accessed,
                struct damon_attrs *attrs)
{
        unsigned int len_window = 1;

        /*
         * sample_interval can be zero, but cannot be larger than
         * aggr_interval, owing to validation of damon_set_attrs().
         */
        if (attrs->sample_interval)
                len_window = damon_max_nr_accesses(attrs);
        r->nr_accesses_bp = damon_moving_sum(r->nr_accesses_bp,
                        r->last_nr_accesses * 10000, len_window,
                        accessed ? 10000 : 0);

        if (accessed)
                r->nr_accesses++;
}

static int __init damon_init(void)
{
        damon_region_cache = KMEM_CACHE(damon_region, 0);
        if (unlikely(!damon_region_cache)) {
                pr_err("creating damon_region_cache fails\n");
                return -ENOMEM;
        }

        return 0;
}

subsys_initcall(damon_init);

#include "core-test.h"