// 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/random.h>
#include <linux/slab.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

/* Get a random number in [l, r) */
#define damon_rand(l, r) (l + prandom_u32_max(r - l))

static DEFINE_MUTEX(damon_lock);
static int nr_running_ctxs;

/*
 * 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);

        return region;
}

/*
 * Add a region between two other regions
 */
inline void damon_insert_region(struct damon_region *r,
                struct damon_region *prev, struct damon_region *next,
                struct damon_target *t)
{
        __list_add(&r->list, &prev->list, &next->list);
        t->nr_regions++;
}

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);
}

/*
 * Construct a damon_target struct
 *
 * Returns the pointer to the new struct if success, or NULL otherwise
 */
struct damon_target *damon_new_target(unsigned long id)
{
        struct damon_target *t;

        t = kmalloc(sizeof(*t), GFP_KERNEL);
        if (!t)
                return NULL;

        t->id = id;
        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);
}

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->primitive_update_interval = 60 * 1000 * 1000;

        ktime_get_coarse_ts64(&ctx->last_aggregation);
        ctx->last_primitive_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);

        return ctx;
}

static void damon_destroy_targets(struct damon_ctx *ctx)
{
        struct damon_target *t, *next_t;

        if (ctx->primitive.cleanup) {
                ctx->primitive.cleanup(ctx);
                return;
        }

        damon_for_each_target_safe(t, next_t, ctx)
                damon_destroy_target(t);
}

void damon_destroy_ctx(struct damon_ctx *ctx)
{
        damon_destroy_targets(ctx);
        kfree(ctx);
}

/**
 * damon_set_targets() - Set monitoring targets.
 * @ctx:        monitoring context
 * @ids:        array of target ids
 * @nr_ids:     number of entries in @ids
 *
 * This function should not be called while the kdamond is running.
 *
 * Return: 0 on success, negative error code otherwise.
 */
int damon_set_targets(struct damon_ctx *ctx,
                      unsigned long *ids, ssize_t nr_ids)
{
        ssize_t i;
        struct damon_target *t, *next;

        damon_destroy_targets(ctx);

        for (i = 0; i < nr_ids; i++) {
                t = damon_new_target(ids[i]);
                if (!t) {
                        pr_err("Failed to alloc damon_target\n");
                        /* The caller should do cleanup of the ids itself */
                        damon_for_each_target_safe(t, next, ctx)
                                damon_destroy_target(t);
                        return -ENOMEM;
                }
                damon_add_target(ctx, t);
        }

        return 0;
}

/**
 * damon_set_attrs() - Set attributes for the monitoring.
 * @ctx:                monitoring context
 * @sample_int:         time interval between samplings
 * @aggr_int:           time interval between aggregations
 * @primitive_upd_int:  time interval between monitoring primitive 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 primitive_upd_int,
                    unsigned long min_nr_reg, unsigned long max_nr_reg)
{
        if (min_nr_reg < 3) {
                pr_err("min_nr_regions (%lu) must be at least 3\n",
                                min_nr_reg);
                return -EINVAL;
        }
        if (min_nr_reg > max_nr_reg) {
                pr_err("invalid nr_regions.  min (%lu) > max (%lu)\n",
                                min_nr_reg, max_nr_reg);
                return -EINVAL;
        }

        ctx->sample_interval = sample_int;
        ctx->aggr_interval = aggr_int;
        ctx->primitive_update_interval = primitive_upd_int;
        ctx->min_nr_regions = min_nr_reg;
        ctx->max_nr_regions = max_nr_reg;

        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 bool damon_kdamond_running(struct damon_ctx *ctx)
{
        bool running;

        mutex_lock(&ctx->kdamond_lock);
        running = ctx->kdamond != NULL;
        mutex_unlock(&ctx->kdamond_lock);

        return running;
}

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_stop = false;
                ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
                                nr_running_ctxs);
                if (IS_ERR(ctx->kdamond)) {
                        err = PTR_ERR(ctx->kdamond);
                        ctx->kdamond = 0;
                }
        }
        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
 *
 * 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 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)
{
        int i;
        int err = 0;

        mutex_lock(&damon_lock);
        if (nr_running_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++;
        }
        mutex_unlock(&damon_lock);

        return err;
}

/*
 * __damon_stop() - Stops monitoring of given context.
 * @ctx:        monitoring context
 *
 * Return: 0 on success, negative error code otherwise.
 */
static int __damon_stop(struct damon_ctx *ctx)
{
        mutex_lock(&ctx->kdamond_lock);
        if (ctx->kdamond) {
                ctx->kdamond_stop = true;
                mutex_unlock(&ctx->kdamond_lock);
                while (damon_kdamond_running(ctx))
                        usleep_range(ctx->sample_interval,
                                        ctx->sample_interval * 2);
                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)
                        return err;
        }

        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;

        damon_for_each_target(t, c) {
                struct damon_region *r;

                damon_for_each_region(r, t) {
                        trace_damon_aggregated(t, r, damon_nr_regions(t));
                        r->nr_accesses = 0;
                }
        }
}

#define sz_damon_region(r) (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->ar.end = r->ar.end;
        damon_destroy_region(r, t);
}

#define diff_of(a, b) (a > b ? a - b : b - a)

/*
 * 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 (prev && prev->ar.end == r->ar.start &&
                    diff_of(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;

        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 target monitoring regions
 *
 * Returns true if it is.
 */
static bool kdamond_need_update_primitive(struct damon_ctx *ctx)
{
        return damon_check_reset_time_interval(&ctx->last_primitive_update,
                        ctx->primitive_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;
        bool stop;

        mutex_lock(&ctx->kdamond_lock);
        stop = ctx->kdamond_stop;
        mutex_unlock(&ctx->kdamond_lock);
        if (stop)
                return true;

        if (!ctx->primitive.target_valid)
                return false;

        damon_for_each_target(t, ctx) {
                if (ctx->primitive.target_valid(t))
                        return false;
        }

        return true;
}

static void set_kdamond_stop(struct damon_ctx *ctx)
{
        mutex_lock(&ctx->kdamond_lock);
        ctx->kdamond_stop = true;
        mutex_unlock(&ctx->kdamond_lock);
}

/*
 * The monitoring daemon that runs as a kernel thread
 */
static int kdamond_fn(void *data)
{
        struct damon_ctx *ctx = (struct damon_ctx *)data;
        struct damon_target *t;
        struct damon_region *r, *next;
        unsigned int max_nr_accesses = 0;
        unsigned long sz_limit = 0;

        mutex_lock(&ctx->kdamond_lock);
        pr_info("kdamond (%d) starts\n", ctx->kdamond->pid);
        mutex_unlock(&ctx->kdamond_lock);

        if (ctx->primitive.init)
                ctx->primitive.init(ctx);
        if (ctx->callback.before_start && ctx->callback.before_start(ctx))
                set_kdamond_stop(ctx);

        sz_limit = damon_region_sz_limit(ctx);

        while (!kdamond_need_stop(ctx)) {
                if (ctx->primitive.prepare_access_checks)
                        ctx->primitive.prepare_access_checks(ctx);
                if (ctx->callback.after_sampling &&
                                ctx->callback.after_sampling(ctx))
                        set_kdamond_stop(ctx);

                usleep_range(ctx->sample_interval, ctx->sample_interval + 1);

                if (ctx->primitive.check_accesses)
                        max_nr_accesses = ctx->primitive.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))
                                set_kdamond_stop(ctx);
                        kdamond_reset_aggregated(ctx);
                        kdamond_split_regions(ctx);
                        if (ctx->primitive.reset_aggregated)
                                ctx->primitive.reset_aggregated(ctx);
                }

                if (kdamond_need_update_primitive(ctx)) {
                        if (ctx->primitive.update)
                                ctx->primitive.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))
                set_kdamond_stop(ctx);
        if (ctx->primitive.cleanup)
                ctx->primitive.cleanup(ctx);

        pr_debug("kdamond (%d) finishes\n", ctx->kdamond->pid);
        mutex_lock(&ctx->kdamond_lock);
        ctx->kdamond = NULL;
        mutex_unlock(&ctx->kdamond_lock);

        mutex_lock(&damon_lock);
        nr_running_ctxs--;
        mutex_unlock(&damon_lock);

        do_exit(0);
}

#include "core-test.h"