// SPDX-License-Identifier: GPL-2.0
/*
 * proactive reclamation: monitor access pattern of a given process, find
 * regions that seems not accessed, and proactively page out the regions.
 */

#define pr_fmt(fmt) "damon_sample_prcl: " fmt

#include <linux/damon.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>

#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "damon_sample_prcl."

static int target_pid __read_mostly;
module_param(target_pid, int, 0600);

static int damon_sample_prcl_enable_store(
                const char *val, const struct kernel_param *kp);

static const struct kernel_param_ops enabled_param_ops = {
        .set = damon_sample_prcl_enable_store,
        .get = param_get_bool,
};

static bool enabled __read_mostly;
module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_PRCL");

static struct damon_ctx *ctx;
static struct pid *target_pidp;

static int damon_sample_prcl_repeat_call_fn(void *data)
{
        struct damon_ctx *c = data;
        struct damon_target *t;

        damon_for_each_target(t, c) {
                struct damon_region *r;
                unsigned long wss = 0;

                damon_for_each_region(r, t) {
                        if (r->nr_accesses > 0)
                                wss += r->ar.end - r->ar.start;
                }
                pr_info("wss: %lu\n", wss);
        }
        return 0;
}

static struct damon_call_control repeat_call_control = {
        .fn = damon_sample_prcl_repeat_call_fn,
        .repeat = true,
};

static int damon_sample_prcl_start(void)
{
        struct damon_target *target;
        struct damos *scheme;
        int err;

        pr_info("start\n");

        ctx = damon_new_ctx();
        if (!ctx)
                return -ENOMEM;
        if (damon_select_ops(ctx, DAMON_OPS_VADDR)) {
                damon_destroy_ctx(ctx);
                return -EINVAL;
        }

        target = damon_new_target();
        if (!target) {
                damon_destroy_ctx(ctx);
                return -ENOMEM;
        }
        damon_add_target(ctx, target);
        target_pidp = find_get_pid(target_pid);
        if (!target_pidp) {
                damon_destroy_ctx(ctx);
                return -EINVAL;
        }
        target->pid = target_pidp;

        scheme = damon_new_scheme(
                        &(struct damos_access_pattern) {
                        .min_sz_region = PAGE_SIZE,
                        .max_sz_region = ULONG_MAX,
                        .min_nr_accesses = 0,
                        .max_nr_accesses = 0,
                        .min_age_region = 50,
                        .max_age_region = UINT_MAX},
                        DAMOS_PAGEOUT,
                        0,
                        &(struct damos_quota){},
                        &(struct damos_watermarks){},
                        NUMA_NO_NODE);
        if (!scheme) {
                damon_destroy_ctx(ctx);
                return -ENOMEM;
        }
        damon_set_schemes(ctx, &scheme, 1);

        err = damon_start(&ctx, 1, true);
        if (err)
                return err;

        repeat_call_control.data = ctx;
        return damon_call(ctx, &repeat_call_control);
}

static void damon_sample_prcl_stop(void)
{
        pr_info("stop\n");
        if (ctx) {
                damon_stop(&ctx, 1);
                damon_destroy_ctx(ctx);
        }
}

static int damon_sample_prcl_enable_store(
                const char *val, const struct kernel_param *kp)
{
        bool is_enabled = enabled;
        int err;

        err = kstrtobool(val, &enabled);
        if (err)
                return err;

        if (enabled == is_enabled)
                return 0;

        if (!damon_initialized())
                return 0;

        if (enabled) {
                err = damon_sample_prcl_start();
                if (err)
                        enabled = false;
                return err;
        }
        damon_sample_prcl_stop();
        return 0;
}

static int __init damon_sample_prcl_init(void)
{
        int err = 0;

        if (!damon_initialized()) {
                if (enabled)
                        enabled = false;
                return -ENOMEM;
        }

        if (enabled) {
                err = damon_sample_prcl_start();
                if (err)
                        enabled = false;
        }
        return 0;
}

module_init(damon_sample_prcl_init);