// SPDX-License-Identifier: GPL-2.0
/*
 * Shows data access monitoring resutls in simple metrics.
 */

#define pr_fmt(fmt) "damon-stat: " fmt

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

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

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

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

static bool enabled __read_mostly = IS_ENABLED(
	CONFIG_DAMON_STAT_ENABLED_DEFAULT);
module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
MODULE_PARM_DESC(enabled, "Enable of disable DAMON_STAT");

static unsigned long estimated_memory_bandwidth __read_mostly;
module_param(estimated_memory_bandwidth, ulong, 0400);
MODULE_PARM_DESC(estimated_memory_bandwidth,
		"Estimated memory bandwidth usage in bytes per second");

static long memory_idle_ms_percentiles[101] __read_mostly = {0,};
module_param_array(memory_idle_ms_percentiles, long, NULL, 0400);
MODULE_PARM_DESC(memory_idle_ms_percentiles,
		"Memory idle time percentiles in milliseconds");

static unsigned long aggr_interval_us;
module_param(aggr_interval_us, ulong, 0400);
MODULE_PARM_DESC(aggr_interval_us,
		"Current tuned aggregation interval in microseconds");

static struct damon_ctx *damon_stat_context;

static unsigned long damon_stat_last_refresh_jiffies;

static void damon_stat_set_estimated_memory_bandwidth(struct damon_ctx *c)
{
	struct damon_target *t;
	struct damon_region *r;
	unsigned long access_bytes = 0;

	damon_for_each_target(t, c) {
		damon_for_each_region(r, t)
			access_bytes += (r->ar.end - r->ar.start) *
				r->nr_accesses;
	}
	estimated_memory_bandwidth = access_bytes * USEC_PER_MSEC *
		MSEC_PER_SEC / c->attrs.aggr_interval;
}

static int damon_stat_idletime(const struct damon_region *r)
{
	if (r->nr_accesses)
		return -1 * (r->age + 1);
	return r->age + 1;
}

static int damon_stat_cmp_regions(const void *a, const void *b)
{
	const struct damon_region *ra = *(const struct damon_region **)a;
	const struct damon_region *rb = *(const struct damon_region **)b;

	return damon_stat_idletime(ra) - damon_stat_idletime(rb);
}

static int damon_stat_sort_regions(struct damon_ctx *c,
		struct damon_region ***sorted_ptr, int *nr_regions_ptr,
		unsigned long *total_sz_ptr)
{
	struct damon_target *t;
	struct damon_region *r;
	struct damon_region **region_pointers;
	unsigned int nr_regions = 0;
	unsigned long total_sz = 0;

	damon_for_each_target(t, c) {
		/* there is only one target */
		region_pointers = kmalloc_array(damon_nr_regions(t),
				sizeof(*region_pointers), GFP_KERNEL);
		if (!region_pointers)
			return -ENOMEM;
		damon_for_each_region(r, t) {
			region_pointers[nr_regions++] = r;
			total_sz += r->ar.end - r->ar.start;
		}
	}
	sort(region_pointers, nr_regions, sizeof(*region_pointers),
			damon_stat_cmp_regions, NULL);
	*sorted_ptr = region_pointers;
	*nr_regions_ptr = nr_regions;
	*total_sz_ptr = total_sz;
	return 0;
}

static void damon_stat_set_idletime_percentiles(struct damon_ctx *c)
{
	struct damon_region **sorted_regions, *region;
	int nr_regions;
	unsigned long total_sz, accounted_bytes = 0;
	int err, i, next_percentile = 0;

	err = damon_stat_sort_regions(c, &sorted_regions, &nr_regions,
			&total_sz);
	if (err)
		return;
	for (i = 0; i < nr_regions; i++) {
		region = sorted_regions[i];
		accounted_bytes += region->ar.end - region->ar.start;
		while (next_percentile <= accounted_bytes * 100 / total_sz)
			memory_idle_ms_percentiles[next_percentile++] =
				damon_stat_idletime(region) *
				(long)c->attrs.aggr_interval / USEC_PER_MSEC;
	}
	kfree(sorted_regions);
}

static int damon_stat_damon_call_fn(void *data)
{
	struct damon_ctx *c = data;

	/* avoid unnecessarily frequent stat update */
	if (time_before_eq(jiffies, damon_stat_last_refresh_jiffies +
				msecs_to_jiffies(5 * MSEC_PER_SEC)))
		return 0;
	damon_stat_last_refresh_jiffies = jiffies;

	aggr_interval_us = c->attrs.aggr_interval;
	damon_stat_set_estimated_memory_bandwidth(c);
	damon_stat_set_idletime_percentiles(c);
	return 0;
}

static struct damon_ctx *damon_stat_build_ctx(void)
{
	struct damon_ctx *ctx;
	struct damon_attrs attrs;
	struct damon_target *target;
	unsigned long start = 0, end = 0;

	ctx = damon_new_ctx();
	if (!ctx)
		return NULL;
	attrs = (struct damon_attrs) {
		.sample_interval = 5 * USEC_PER_MSEC,
		.aggr_interval = 100 * USEC_PER_MSEC,
		.ops_update_interval = 60 * USEC_PER_MSEC * MSEC_PER_SEC,
		.min_nr_regions = 10,
		.max_nr_regions = 1000,
	};
	/*
	 * auto-tune sampling and aggregation interval aiming 4% DAMON-observed
	 * accesses ratio, keeping sampling interval in [5ms, 10s] range.
	 */
	attrs.intervals_goal = (struct damon_intervals_goal) {
		.access_bp = 400, .aggrs = 3,
		.min_sample_us = 5000, .max_sample_us = 10000000,
	};
	if (damon_set_attrs(ctx, &attrs))
		goto free_out;

	/*
	 * auto-tune sampling and aggregation interval aiming 4% DAMON-observed
	 * accesses ratio, keeping sampling interval in [5ms, 10s] range.
	 */
	ctx->attrs.intervals_goal = (struct damon_intervals_goal) {
		.access_bp = 400, .aggrs = 3,
		.min_sample_us = 5000, .max_sample_us = 10000000,
	};
	if (damon_select_ops(ctx, DAMON_OPS_PADDR))
		goto free_out;

	target = damon_new_target();
	if (!target)
		goto free_out;
	damon_add_target(ctx, target);
	if (damon_set_region_biggest_system_ram_default(target, &start, &end))
		goto free_out;
	return ctx;
free_out:
	damon_destroy_ctx(ctx);
	return NULL;
}

static struct damon_call_control call_control = {
	.fn = damon_stat_damon_call_fn,
	.repeat = true,
};

static int damon_stat_start(void)
{
	int err;

	damon_stat_context = damon_stat_build_ctx();
	if (!damon_stat_context)
		return -ENOMEM;
	err = damon_start(&damon_stat_context, 1, true);
	if (err)
		return err;

	damon_stat_last_refresh_jiffies = jiffies;
	call_control.data = damon_stat_context;
	return damon_call(damon_stat_context, &call_control);
}

static void damon_stat_stop(void)
{
	damon_stop(&damon_stat_context, 1);
	damon_destroy_ctx(damon_stat_context);
}

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

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

	if (is_enabled == enabled)
		return 0;

	if (!damon_initialized())
		/*
		 * probably called from command line parsing (parse_args()).
		 * Cannot call damon_new_ctx().  Let damon_stat_init() handle.
		 */
		return 0;

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

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

	if (!damon_initialized()) {
		err = -ENOMEM;
		goto out;
	}

	/* probably set via command line */
	if (enabled)
		err = damon_stat_start();

out:
	if (err && enabled)
		enabled = false;
	return err;
}

module_init(damon_stat_init);