mm/damon/lru_sort.c - linux/kernel/git/torvalds/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * DAMON-based LRU-lists Sorting
  *
  * Author: SeongJae Park <sj@kernel.org>
  */

 #define pr_fmt(fmt) "damon-lru-sort: " fmt

 #include <linux/damon.h>
 #include <linux/ioport.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/workqueue.h>

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

 /*
  * Enable or disable DAMON_LRU_SORT.
  *
  * You can enable DAMON_LRU_SORT by setting the value of this parameter as
  * ``Y``.  Setting it as ``N`` disables DAMON_LRU_SORT.  Note that
  * DAMON_LRU_SORT could do no real monitoring and LRU-lists sorting due to the
  * watermarks-based activation condition.  Refer to below descriptions for the
  * watermarks parameter for this.
  */
 static bool enabled __read_mostly;

 /*
  * Make DAMON_LRU_SORT reads the input parameters again, except ``enabled``.
  *
  * Input parameters that updated while DAMON_LRU_SORT is running are not
  * applied by default.  Once this parameter is set as ``Y``, DAMON_LRU_SORT
  * reads values of parametrs except ``enabled`` again.  Once the re-reading is
  * done, this parameter is set as ``N``.  If invalid parameters are found while
  * the re-reading, DAMON_LRU_SORT will be disabled.
  */
 static bool commit_inputs __read_mostly;
 module_param(commit_inputs, bool, 0600);

 /*
  * Access frequency threshold for hot memory regions identification in permil.
  *
  * If a memory region is accessed in frequency of this or higher,
  * DAMON_LRU_SORT identifies the region as hot, and mark it as accessed on the
  * LRU list, so that it could not be reclaimed under memory pressure.  50% by
  * default.
  */
 static unsigned long hot_thres_access_freq = 500;
 module_param(hot_thres_access_freq, ulong, 0600);

 /*
  * Time threshold for cold memory regions identification in microseconds.
  *
  * If a memory region is not accessed for this or longer time, DAMON_LRU_SORT
  * identifies the region as cold, and mark it as unaccessed on the LRU list, so
  * that it could be reclaimed first under memory pressure.  120 seconds by
  * default.
  */
 static unsigned long cold_min_age __read_mostly = 120000000;
 module_param(cold_min_age, ulong, 0600);

 /*
  * Limit of time for trying the LRU lists sorting in milliseconds.
  *
  * DAMON_LRU_SORT tries to use only up to this time within a time window
  * (quota_reset_interval_ms) for trying LRU lists sorting.  This can be used
  * for limiting CPU consumption of DAMON_LRU_SORT.  If the value is zero, the
  * limit is disabled.
  *
  * 10 ms by default.
  */
 static unsigned long quota_ms __read_mostly = 10;
 module_param(quota_ms, ulong, 0600);

 /*
  * The time quota charge reset interval in milliseconds.
  *
  * The charge reset interval for the quota of time (quota_ms).  That is,
  * DAMON_LRU_SORT does not try LRU-lists sorting for more than quota_ms
  * milliseconds or quota_sz bytes within quota_reset_interval_ms milliseconds.
  *
  * 1 second by default.
  */
 static unsigned long quota_reset_interval_ms __read_mostly = 1000;
 module_param(quota_reset_interval_ms, ulong, 0600);

 /*
  * The watermarks check time interval in microseconds.
  *
  * Minimal time to wait before checking the watermarks, when DAMON_LRU_SORT is
  * enabled but inactive due to its watermarks rule.  5 seconds by default.
  */
 static unsigned long wmarks_interval __read_mostly = 5000000;
 module_param(wmarks_interval, ulong, 0600);

 /*
  * Free memory rate (per thousand) for the high watermark.
  *
  * If free memory of the system in bytes per thousand bytes is higher than
  * this, DAMON_LRU_SORT becomes inactive, so it does nothing but periodically
  * checks the watermarks.  200 (20%) by default.
  */
 static unsigned long wmarks_high __read_mostly = 200;
 module_param(wmarks_high, ulong, 0600);

 /*
  * Free memory rate (per thousand) for the middle watermark.
  *
  * If free memory of the system in bytes per thousand bytes is between this and
  * the low watermark, DAMON_LRU_SORT becomes active, so starts the monitoring
  * and the LRU-lists sorting.  150 (15%) by default.
  */
 static unsigned long wmarks_mid __read_mostly = 150;
 module_param(wmarks_mid, ulong, 0600);

 /*
  * Free memory rate (per thousand) for the low watermark.
  *
  * If free memory of the system in bytes per thousand bytes is lower than this,
  * DAMON_LRU_SORT becomes inactive, so it does nothing but periodically checks
  * the watermarks.  50 (5%) by default.
  */
 static unsigned long wmarks_low __read_mostly = 50;
 module_param(wmarks_low, ulong, 0600);

 /*
  * Sampling interval for the monitoring in microseconds.
  *
  * The sampling interval of DAMON for the hot/cold memory monitoring.  Please
  * refer to the DAMON documentation for more detail.  5 ms by default.
  */
 static unsigned long sample_interval __read_mostly = 5000;
 module_param(sample_interval, ulong, 0600);

 /*
  * Aggregation interval for the monitoring in microseconds.
  *
  * The aggregation interval of DAMON for the hot/cold memory monitoring.
  * Please refer to the DAMON documentation for more detail.  100 ms by default.
  */
 static unsigned long aggr_interval __read_mostly = 100000;
 module_param(aggr_interval, ulong, 0600);

 /*
  * Minimum number of monitoring regions.
  *
  * The minimal number of monitoring regions of DAMON for the hot/cold memory
  * monitoring.  This can be used to set lower-bound of the monitoring quality.
  * But, setting this too high could result in increased monitoring overhead.
  * Please refer to the DAMON documentation for more detail.  10 by default.
  */
 static unsigned long min_nr_regions __read_mostly = 10;
 module_param(min_nr_regions, ulong, 0600);

 /*
  * Maximum number of monitoring regions.
  *
  * The maximum number of monitoring regions of DAMON for the hot/cold memory
  * monitoring.  This can be used to set upper-bound of the monitoring overhead.
  * However, setting this too low could result in bad monitoring quality.
  * Please refer to the DAMON documentation for more detail.  1000 by default.
  */
 static unsigned long max_nr_regions __read_mostly = 1000;
 module_param(max_nr_regions, ulong, 0600);

 /*
  * Start of the target memory region in physical address.
  *
  * The start physical address of memory region that DAMON_LRU_SORT will do work
  * against.  By default, biggest System RAM is used as the region.
  */
 static unsigned long monitor_region_start __read_mostly;
 module_param(monitor_region_start, ulong, 0600);

 /*
  * End of the target memory region in physical address.
  *
  * The end physical address of memory region that DAMON_LRU_SORT will do work
  * against.  By default, biggest System RAM is used as the region.
  */
 static unsigned long monitor_region_end __read_mostly;
 module_param(monitor_region_end, ulong, 0600);

 /*
  * PID of the DAMON thread
  *
  * If DAMON_LRU_SORT is enabled, this becomes the PID of the worker thread.
  * Else, -1.
  */
 static int kdamond_pid __read_mostly = -1;
 module_param(kdamond_pid, int, 0400);

 /*
  * Number of hot memory regions that tried to be LRU-sorted.
  */
 static unsigned long nr_lru_sort_tried_hot_regions __read_mostly;
 module_param(nr_lru_sort_tried_hot_regions, ulong, 0400);

 /*
  * Total bytes of hot memory regions that tried to be LRU-sorted.
  */
 static unsigned long bytes_lru_sort_tried_hot_regions __read_mostly;
 module_param(bytes_lru_sort_tried_hot_regions, ulong, 0400);

 /*
  * Number of hot memory regions that successfully be LRU-sorted.
  */
 static unsigned long nr_lru_sorted_hot_regions __read_mostly;
 module_param(nr_lru_sorted_hot_regions, ulong, 0400);

 /*
  * Total bytes of hot memory regions that successfully be LRU-sorted.
  */
 static unsigned long bytes_lru_sorted_hot_regions __read_mostly;
 module_param(bytes_lru_sorted_hot_regions, ulong, 0400);

 /*
  * Number of times that the time quota limit for hot regions have exceeded
  */
 static unsigned long nr_hot_quota_exceeds __read_mostly;
 module_param(nr_hot_quota_exceeds, ulong, 0400);

 /*
  * Number of cold memory regions that tried to be LRU-sorted.
  */
 static unsigned long nr_lru_sort_tried_cold_regions __read_mostly;
 module_param(nr_lru_sort_tried_cold_regions, ulong, 0400);

 /*
  * Total bytes of cold memory regions that tried to be LRU-sorted.
  */
 static unsigned long bytes_lru_sort_tried_cold_regions __read_mostly;
 module_param(bytes_lru_sort_tried_cold_regions, ulong, 0400);

 /*
  * Number of cold memory regions that successfully be LRU-sorted.
  */
 static unsigned long nr_lru_sorted_cold_regions __read_mostly;
 module_param(nr_lru_sorted_cold_regions, ulong, 0400);

 /*
  * Total bytes of cold memory regions that successfully be LRU-sorted.
  */
 static unsigned long bytes_lru_sorted_cold_regions __read_mostly;
 module_param(bytes_lru_sorted_cold_regions, ulong, 0400);

 /*
  * Number of times that the time quota limit for cold regions have exceeded
  */
 static unsigned long nr_cold_quota_exceeds __read_mostly;
 module_param(nr_cold_quota_exceeds, ulong, 0400);

 static struct damon_ctx *ctx;
 static struct damon_target *target;

 struct damon_lru_sort_ram_walk_arg {
 	unsigned long start;
 	unsigned long end;
 };

 static int walk_system_ram(struct resource *res, void *arg)
 {
 	struct damon_lru_sort_ram_walk_arg *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 get_monitoring_region(unsigned long *start, unsigned long *end)
 {
 	struct damon_lru_sort_ram_walk_arg 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;
 }

 /* Create a DAMON-based operation scheme for hot memory regions */
 static struct damos *damon_lru_sort_new_hot_scheme(unsigned int hot_thres)
 {
 	struct damos_watermarks wmarks = {
 		.metric = DAMOS_WMARK_FREE_MEM_RATE,
 		.interval = wmarks_interval,
 		.high = wmarks_high,
 		.mid = wmarks_mid,
 		.low = wmarks_low,
 	};
 	struct damos_quota quota = {
 		/*
 		 * Do not try LRU-lists sorting of hot pages for more than half
 		 * of quota_ms milliseconds within quota_reset_interval_ms.
 		 */
 		.ms = quota_ms / 2,
 		.sz = 0,
 		.reset_interval = quota_reset_interval_ms,
 		/* Within the quota, mark hotter regions accessed first. */
 		.weight_sz = 0,
 		.weight_nr_accesses = 1,
 		.weight_age = 0,
 	};
 	struct damos *scheme = damon_new_scheme(
 			/* Find regions having PAGE_SIZE or larger size */
 			PAGE_SIZE, ULONG_MAX,
 			/* and accessed for more than the threshold */
 			hot_thres, UINT_MAX,
 			/* no matter its age */
 			0, UINT_MAX,
 			/* prioritize those on LRU lists, as soon as found */
 			DAMOS_LRU_PRIO,
 			/* under the quota. */
 			&quota,
 			/* (De)activate this according to the watermarks. */
 			&wmarks);

 	return scheme;
 }

 /* Create a DAMON-based operation scheme for cold memory regions */
 static struct damos *damon_lru_sort_new_cold_scheme(unsigned int cold_thres)
 {
 	struct damos_watermarks wmarks = {
 		.metric = DAMOS_WMARK_FREE_MEM_RATE,
 		.interval = wmarks_interval,
 		.high = wmarks_high,
 		.mid = wmarks_mid,
 		.low = wmarks_low,
 	};
 	struct damos_quota quota = {
 		/*
 		 * Do not try LRU-lists sorting of cold pages for more than
 		 * half of quota_ms milliseconds within
 		 * quota_reset_interval_ms.
 		 */
 		.ms = quota_ms / 2,
 		.sz = 0,
 		.reset_interval = quota_reset_interval_ms,
 		/* Within the quota, mark colder regions not accessed first. */
 		.weight_sz = 0,
 		.weight_nr_accesses = 0,
 		.weight_age = 1,
 	};
 	struct damos *scheme = damon_new_scheme(
 			/* Find regions having PAGE_SIZE or larger size */
 			PAGE_SIZE, ULONG_MAX,
 			/* and not accessed at all */
 			0, 0,
 			/* for cold_thres or more micro-seconds, and */
 			cold_thres, UINT_MAX,
 			/* mark those as not accessed, as soon as found */
 			DAMOS_LRU_DEPRIO,
 			/* under the quota. */
 			&quota,
 			/* (De)activate this according to the watermarks. */
 			&wmarks);

 	return scheme;
 }

 static int damon_lru_sort_apply_parameters(void)
 {
 	struct damos *scheme, *next_scheme;
 	struct damon_addr_range addr_range;
 	unsigned int hot_thres, cold_thres;
 	int err = 0;

 	err = damon_set_attrs(ctx, sample_interval, aggr_interval, 0,
 			min_nr_regions, max_nr_regions);
 	if (err)
 		return err;

 	/* free previously set schemes */
 	damon_for_each_scheme_safe(scheme, next_scheme, ctx)
 		damon_destroy_scheme(scheme);

 	/* aggr_interval / sample_interval is the maximum nr_accesses */
 	hot_thres = aggr_interval / sample_interval * hot_thres_access_freq /
 		1000;
 	scheme = damon_lru_sort_new_hot_scheme(hot_thres);
 	if (!scheme)
 		return -ENOMEM;
 	damon_add_scheme(ctx, scheme);

 	cold_thres = cold_min_age / aggr_interval;
 	scheme = damon_lru_sort_new_cold_scheme(cold_thres);
 	if (!scheme)
 		return -ENOMEM;
 	damon_add_scheme(ctx, scheme);

 	if (monitor_region_start > monitor_region_end)
 		return -EINVAL;
 	if (!monitor_region_start && !monitor_region_end &&
 			!get_monitoring_region(&monitor_region_start,
 				&monitor_region_end))
 		return -EINVAL;
 	addr_range.start = monitor_region_start;
 	addr_range.end = monitor_region_end;
 	return damon_set_regions(target, &addr_range, 1);
 }

 static int damon_lru_sort_turn(bool on)
 {
 	int err;

 	if (!on) {
 		err = damon_stop(&ctx, 1);
 		if (!err)
 			kdamond_pid = -1;
 		return err;
 	}

 	err = damon_lru_sort_apply_parameters();
 	if (err)
 		return err;

 	err = damon_start(&ctx, 1, true);
 	if (err)
 		return err;
 	kdamond_pid = ctx->kdamond->pid;
 	return 0;
 }

 static struct delayed_work damon_lru_sort_timer;
 static void damon_lru_sort_timer_fn(struct work_struct *work)
 {
 	static bool last_enabled;
 	bool now_enabled;

 	now_enabled = enabled;
 	if (last_enabled != now_enabled) {
 		if (!damon_lru_sort_turn(now_enabled))
 			last_enabled = now_enabled;
 		else
 			enabled = last_enabled;
 	}
 }
 static DECLARE_DELAYED_WORK(damon_lru_sort_timer, damon_lru_sort_timer_fn);

 static bool damon_lru_sort_initialized;

 static int damon_lru_sort_enabled_store(const char *val,
 		const struct kernel_param *kp)
 {
 	int rc = param_set_bool(val, kp);

 	if (rc < 0)
 		return rc;

 	if (!damon_lru_sort_initialized)
 		return rc;

 	schedule_delayed_work(&damon_lru_sort_timer, 0);

 	return 0;
 }

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

 module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
 MODULE_PARM_DESC(enabled,
 	"Enable or disable DAMON_LRU_SORT (default: disabled)");

 static int damon_lru_sort_handle_commit_inputs(void)
 {
 	int err;

 	if (!commit_inputs)
 		return 0;

 	err = damon_lru_sort_apply_parameters();
 	commit_inputs = false;
 	return err;
 }

 static int damon_lru_sort_after_aggregation(struct damon_ctx *c)
 {
 	struct damos *s;

 	/* update the stats parameter */
 	damon_for_each_scheme(s, c) {
 		if (s->action == DAMOS_LRU_PRIO) {
 			nr_lru_sort_tried_hot_regions = s->stat.nr_tried;
 			bytes_lru_sort_tried_hot_regions = s->stat.sz_tried;
 			nr_lru_sorted_hot_regions = s->stat.nr_applied;
 			bytes_lru_sorted_hot_regions = s->stat.sz_applied;
 			nr_hot_quota_exceeds = s->stat.qt_exceeds;
 		} else if (s->action == DAMOS_LRU_DEPRIO) {
 			nr_lru_sort_tried_cold_regions = s->stat.nr_tried;
 			bytes_lru_sort_tried_cold_regions = s->stat.sz_tried;
 			nr_lru_sorted_cold_regions = s->stat.nr_applied;
 			bytes_lru_sorted_cold_regions = s->stat.sz_applied;
 			nr_cold_quota_exceeds = s->stat.qt_exceeds;
 		}
 	}

 	return damon_lru_sort_handle_commit_inputs();
 }

 static int damon_lru_sort_after_wmarks_check(struct damon_ctx *c)
 {
 	return damon_lru_sort_handle_commit_inputs();
 }

 static int __init damon_lru_sort_init(void)
 {
 	ctx = damon_new_ctx();
 	if (!ctx)
 		return -ENOMEM;

 	if (damon_select_ops(ctx, DAMON_OPS_PADDR)) {
 		damon_destroy_ctx(ctx);
 		return -EINVAL;
 	}

 	ctx->callback.after_wmarks_check = damon_lru_sort_after_wmarks_check;
 	ctx->callback.after_aggregation = damon_lru_sort_after_aggregation;

 	target = damon_new_target();
 	if (!target) {
 		damon_destroy_ctx(ctx);
 		return -ENOMEM;
 	}
 	damon_add_target(ctx, target);

 	schedule_delayed_work(&damon_lru_sort_timer, 0);

 	damon_lru_sort_initialized = true;
 	return 0;
 }

 module_init(damon_lru_sort_init);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* DAMON-based LRU-lists Sorting
	*
	* Author: SeongJae Park <sj@kernel.org>
	*/

	#define pr_fmt(fmt) "damon-lru-sort: " fmt

	#include <linux/damon.h>
	#include <linux/ioport.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/workqueue.h>

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

	/*
	* Enable or disable DAMON_LRU_SORT.
	*
	* You can enable DAMON_LRU_SORT by setting the value of this parameter as
	* ``Y``. Setting it as ``N`` disables DAMON_LRU_SORT. Note that
	* DAMON_LRU_SORT could do no real monitoring and LRU-lists sorting due to the
	* watermarks-based activation condition. Refer to below descriptions for the
	* watermarks parameter for this.
	*/
	static bool enabled __read_mostly;

	/*
	* Make DAMON_LRU_SORT reads the input parameters again, except ``enabled``.
	*
	* Input parameters that updated while DAMON_LRU_SORT is running are not
	* applied by default. Once this parameter is set as ``Y``, DAMON_LRU_SORT
	* reads values of parametrs except ``enabled`` again. Once the re-reading is
	* done, this parameter is set as ``N``. If invalid parameters are found while
	* the re-reading, DAMON_LRU_SORT will be disabled.
	*/
	static bool commit_inputs __read_mostly;
	module_param(commit_inputs, bool, 0600);

	/*
	* Access frequency threshold for hot memory regions identification in permil.
	*
	* If a memory region is accessed in frequency of this or higher,
	* DAMON_LRU_SORT identifies the region as hot, and mark it as accessed on the
	* LRU list, so that it could not be reclaimed under memory pressure. 50% by
	* default.
	*/
	static unsigned long hot_thres_access_freq = 500;
	module_param(hot_thres_access_freq, ulong, 0600);

	/*
	* Time threshold for cold memory regions identification in microseconds.
	*
	* If a memory region is not accessed for this or longer time, DAMON_LRU_SORT
	* identifies the region as cold, and mark it as unaccessed on the LRU list, so
	* that it could be reclaimed first under memory pressure. 120 seconds by
	* default.
	*/
	static unsigned long cold_min_age __read_mostly = 120000000;
	module_param(cold_min_age, ulong, 0600);

	/*
	* Limit of time for trying the LRU lists sorting in milliseconds.
	*
	* DAMON_LRU_SORT tries to use only up to this time within a time window
	* (quota_reset_interval_ms) for trying LRU lists sorting. This can be used
	* for limiting CPU consumption of DAMON_LRU_SORT. If the value is zero, the
	* limit is disabled.
	*
	* 10 ms by default.
	*/
	static unsigned long quota_ms __read_mostly = 10;
	module_param(quota_ms, ulong, 0600);

	/*
	* The time quota charge reset interval in milliseconds.
	*
	* The charge reset interval for the quota of time (quota_ms). That is,
	* DAMON_LRU_SORT does not try LRU-lists sorting for more than quota_ms
	* milliseconds or quota_sz bytes within quota_reset_interval_ms milliseconds.
	*
	* 1 second by default.
	*/
	static unsigned long quota_reset_interval_ms __read_mostly = 1000;
	module_param(quota_reset_interval_ms, ulong, 0600);

	/*
	* The watermarks check time interval in microseconds.
	*
	* Minimal time to wait before checking the watermarks, when DAMON_LRU_SORT is
	* enabled but inactive due to its watermarks rule. 5 seconds by default.
	*/
	static unsigned long wmarks_interval __read_mostly = 5000000;
	module_param(wmarks_interval, ulong, 0600);

	/*
	* Free memory rate (per thousand) for the high watermark.
	*
	* If free memory of the system in bytes per thousand bytes is higher than
	* this, DAMON_LRU_SORT becomes inactive, so it does nothing but periodically
	* checks the watermarks. 200 (20%) by default.
	*/
	static unsigned long wmarks_high __read_mostly = 200;
	module_param(wmarks_high, ulong, 0600);

	/*
	* Free memory rate (per thousand) for the middle watermark.
	*
	* If free memory of the system in bytes per thousand bytes is between this and
	* the low watermark, DAMON_LRU_SORT becomes active, so starts the monitoring
	* and the LRU-lists sorting. 150 (15%) by default.
	*/
	static unsigned long wmarks_mid __read_mostly = 150;
	module_param(wmarks_mid, ulong, 0600);

	/*
	* Free memory rate (per thousand) for the low watermark.
	*
	* If free memory of the system in bytes per thousand bytes is lower than this,
	* DAMON_LRU_SORT becomes inactive, so it does nothing but periodically checks
	* the watermarks. 50 (5%) by default.
	*/
	static unsigned long wmarks_low __read_mostly = 50;
	module_param(wmarks_low, ulong, 0600);

	/*
	* Sampling interval for the monitoring in microseconds.
	*
	* The sampling interval of DAMON for the hot/cold memory monitoring. Please
	* refer to the DAMON documentation for more detail. 5 ms by default.
	*/
	static unsigned long sample_interval __read_mostly = 5000;
	module_param(sample_interval, ulong, 0600);

	/*
	* Aggregation interval for the monitoring in microseconds.
	*
	* The aggregation interval of DAMON for the hot/cold memory monitoring.
	* Please refer to the DAMON documentation for more detail. 100 ms by default.
	*/
	static unsigned long aggr_interval __read_mostly = 100000;
	module_param(aggr_interval, ulong, 0600);

	/*
	* Minimum number of monitoring regions.
	*
	* The minimal number of monitoring regions of DAMON for the hot/cold memory
	* monitoring. This can be used to set lower-bound of the monitoring quality.
	* But, setting this too high could result in increased monitoring overhead.
	* Please refer to the DAMON documentation for more detail. 10 by default.
	*/
	static unsigned long min_nr_regions __read_mostly = 10;
	module_param(min_nr_regions, ulong, 0600);

	/*
	* Maximum number of monitoring regions.
	*
	* The maximum number of monitoring regions of DAMON for the hot/cold memory
	* monitoring. This can be used to set upper-bound of the monitoring overhead.
	* However, setting this too low could result in bad monitoring quality.
	* Please refer to the DAMON documentation for more detail. 1000 by default.
	*/
	static unsigned long max_nr_regions __read_mostly = 1000;
	module_param(max_nr_regions, ulong, 0600);

	/*
	* Start of the target memory region in physical address.
	*
	* The start physical address of memory region that DAMON_LRU_SORT will do work
	* against. By default, biggest System RAM is used as the region.
	*/
	static unsigned long monitor_region_start __read_mostly;
	module_param(monitor_region_start, ulong, 0600);

	/*
	* End of the target memory region in physical address.
	*
	* The end physical address of memory region that DAMON_LRU_SORT will do work
	* against. By default, biggest System RAM is used as the region.
	*/
	static unsigned long monitor_region_end __read_mostly;
	module_param(monitor_region_end, ulong, 0600);

	/*
	* PID of the DAMON thread
	*
	* If DAMON_LRU_SORT is enabled, this becomes the PID of the worker thread.
	* Else, -1.
	*/
	static int kdamond_pid __read_mostly = -1;
	module_param(kdamond_pid, int, 0400);

	/*
	* Number of hot memory regions that tried to be LRU-sorted.
	*/
	static unsigned long nr_lru_sort_tried_hot_regions __read_mostly;
	module_param(nr_lru_sort_tried_hot_regions, ulong, 0400);

	/*
	* Total bytes of hot memory regions that tried to be LRU-sorted.
	*/
	static unsigned long bytes_lru_sort_tried_hot_regions __read_mostly;
	module_param(bytes_lru_sort_tried_hot_regions, ulong, 0400);

	/*
	* Number of hot memory regions that successfully be LRU-sorted.
	*/
	static unsigned long nr_lru_sorted_hot_regions __read_mostly;
	module_param(nr_lru_sorted_hot_regions, ulong, 0400);

	/*
	* Total bytes of hot memory regions that successfully be LRU-sorted.
	*/
	static unsigned long bytes_lru_sorted_hot_regions __read_mostly;
	module_param(bytes_lru_sorted_hot_regions, ulong, 0400);

	/*
	* Number of times that the time quota limit for hot regions have exceeded
	*/
	static unsigned long nr_hot_quota_exceeds __read_mostly;
	module_param(nr_hot_quota_exceeds, ulong, 0400);

	/*
	* Number of cold memory regions that tried to be LRU-sorted.
	*/
	static unsigned long nr_lru_sort_tried_cold_regions __read_mostly;
	module_param(nr_lru_sort_tried_cold_regions, ulong, 0400);

	/*
	* Total bytes of cold memory regions that tried to be LRU-sorted.
	*/
	static unsigned long bytes_lru_sort_tried_cold_regions __read_mostly;
	module_param(bytes_lru_sort_tried_cold_regions, ulong, 0400);

	/*
	* Number of cold memory regions that successfully be LRU-sorted.
	*/
	static unsigned long nr_lru_sorted_cold_regions __read_mostly;
	module_param(nr_lru_sorted_cold_regions, ulong, 0400);

	/*
	* Total bytes of cold memory regions that successfully be LRU-sorted.
	*/
	static unsigned long bytes_lru_sorted_cold_regions __read_mostly;
	module_param(bytes_lru_sorted_cold_regions, ulong, 0400);

	/*
	* Number of times that the time quota limit for cold regions have exceeded
	*/
	static unsigned long nr_cold_quota_exceeds __read_mostly;
	module_param(nr_cold_quota_exceeds, ulong, 0400);

	static struct damon_ctx *ctx;
	static struct damon_target *target;

	struct damon_lru_sort_ram_walk_arg {
	unsigned long start;
	unsigned long end;
	};

	static int walk_system_ram(struct resource res, void arg)
	{
	struct damon_lru_sort_ram_walk_arg *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 get_monitoring_region(unsigned long start, unsigned long end)
	{
	struct damon_lru_sort_ram_walk_arg 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;
	}

	/* Create a DAMON-based operation scheme for hot memory regions */
	static struct damos *damon_lru_sort_new_hot_scheme(unsigned int hot_thres)
	{
	struct damos_watermarks wmarks = {
	.metric = DAMOS_WMARK_FREE_MEM_RATE,
	.interval = wmarks_interval,
	.high = wmarks_high,
	.mid = wmarks_mid,
	.low = wmarks_low,
	};
	struct damos_quota quota = {
	/*
	* Do not try LRU-lists sorting of hot pages for more than half
	* of quota_ms milliseconds within quota_reset_interval_ms.
	*/
	.ms = quota_ms / 2,
	.sz = 0,
	.reset_interval = quota_reset_interval_ms,
	/* Within the quota, mark hotter regions accessed first. */
	.weight_sz = 0,
	.weight_nr_accesses = 1,
	.weight_age = 0,
	};
	struct damos *scheme = damon_new_scheme(
	/* Find regions having PAGE_SIZE or larger size */
	PAGE_SIZE, ULONG_MAX,
	/* and accessed for more than the threshold */
	hot_thres, UINT_MAX,
	/* no matter its age */
	0, UINT_MAX,
	/* prioritize those on LRU lists, as soon as found */
	DAMOS_LRU_PRIO,
	/* under the quota. */
	&quota,
	/* (De)activate this according to the watermarks. */
	&wmarks);

	return scheme;
	}

	/* Create a DAMON-based operation scheme for cold memory regions */
	static struct damos *damon_lru_sort_new_cold_scheme(unsigned int cold_thres)
	{
	struct damos_watermarks wmarks = {
	.metric = DAMOS_WMARK_FREE_MEM_RATE,
	.interval = wmarks_interval,
	.high = wmarks_high,
	.mid = wmarks_mid,
	.low = wmarks_low,
	};
	struct damos_quota quota = {
	/*
	* Do not try LRU-lists sorting of cold pages for more than
	* half of quota_ms milliseconds within
	* quota_reset_interval_ms.
	*/
	.ms = quota_ms / 2,
	.sz = 0,
	.reset_interval = quota_reset_interval_ms,
	/* Within the quota, mark colder regions not accessed first. */
	.weight_sz = 0,
	.weight_nr_accesses = 0,
	.weight_age = 1,
	};
	struct damos *scheme = damon_new_scheme(
	/* Find regions having PAGE_SIZE or larger size */
	PAGE_SIZE, ULONG_MAX,
	/* and not accessed at all */
	0, 0,
	/* for cold_thres or more micro-seconds, and */
	cold_thres, UINT_MAX,
	/* mark those as not accessed, as soon as found */
	DAMOS_LRU_DEPRIO,
	/* under the quota. */
	&quota,
	/* (De)activate this according to the watermarks. */
	&wmarks);

	return scheme;
	}

	static int damon_lru_sort_apply_parameters(void)
	{
	struct damos scheme, next_scheme;
	struct damon_addr_range addr_range;
	unsigned int hot_thres, cold_thres;
	int err = 0;

	err = damon_set_attrs(ctx, sample_interval, aggr_interval, 0,
	min_nr_regions, max_nr_regions);
	if (err)
	return err;

	/* free previously set schemes */
	damon_for_each_scheme_safe(scheme, next_scheme, ctx)
	damon_destroy_scheme(scheme);

	/* aggr_interval / sample_interval is the maximum nr_accesses */
	hot_thres = aggr_interval / sample_interval * hot_thres_access_freq /
	1000;
	scheme = damon_lru_sort_new_hot_scheme(hot_thres);
	if (!scheme)
	return -ENOMEM;
	damon_add_scheme(ctx, scheme);

	cold_thres = cold_min_age / aggr_interval;
	scheme = damon_lru_sort_new_cold_scheme(cold_thres);
	if (!scheme)
	return -ENOMEM;
	damon_add_scheme(ctx, scheme);

	if (monitor_region_start > monitor_region_end)
	return -EINVAL;
	if (!monitor_region_start && !monitor_region_end &&
	!get_monitoring_region(&monitor_region_start,
	&monitor_region_end))
	return -EINVAL;
	addr_range.start = monitor_region_start;
	addr_range.end = monitor_region_end;
	return damon_set_regions(target, &addr_range, 1);
	}

	static int damon_lru_sort_turn(bool on)
	{
	int err;

	if (!on) {
	err = damon_stop(&ctx, 1);
	if (!err)
	kdamond_pid = -1;
	return err;
	}

	err = damon_lru_sort_apply_parameters();
	if (err)
	return err;

	err = damon_start(&ctx, 1, true);
	if (err)
	return err;
	kdamond_pid = ctx->kdamond->pid;
	return 0;
	}

	static struct delayed_work damon_lru_sort_timer;
	static void damon_lru_sort_timer_fn(struct work_struct *work)
	{
	static bool last_enabled;
	bool now_enabled;

	now_enabled = enabled;
	if (last_enabled != now_enabled) {
	if (!damon_lru_sort_turn(now_enabled))
	last_enabled = now_enabled;
	else
	enabled = last_enabled;
	}
	}
	static DECLARE_DELAYED_WORK(damon_lru_sort_timer, damon_lru_sort_timer_fn);

	static bool damon_lru_sort_initialized;

	static int damon_lru_sort_enabled_store(const char *val,
	const struct kernel_param *kp)
	{
	int rc = param_set_bool(val, kp);

	if (rc < 0)
	return rc;

	if (!damon_lru_sort_initialized)
	return rc;

	schedule_delayed_work(&damon_lru_sort_timer, 0);

	return 0;
	}

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

	module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
	MODULE_PARM_DESC(enabled,
	"Enable or disable DAMON_LRU_SORT (default: disabled)");

	static int damon_lru_sort_handle_commit_inputs(void)
	{
	int err;

	if (!commit_inputs)
	return 0;

	err = damon_lru_sort_apply_parameters();
	commit_inputs = false;
	return err;
	}

	static int damon_lru_sort_after_aggregation(struct damon_ctx *c)
	{
	struct damos *s;

	/* update the stats parameter */
	damon_for_each_scheme(s, c) {
	if (s->action == DAMOS_LRU_PRIO) {
	nr_lru_sort_tried_hot_regions = s->stat.nr_tried;
	bytes_lru_sort_tried_hot_regions = s->stat.sz_tried;
	nr_lru_sorted_hot_regions = s->stat.nr_applied;
	bytes_lru_sorted_hot_regions = s->stat.sz_applied;
	nr_hot_quota_exceeds = s->stat.qt_exceeds;
	} else if (s->action == DAMOS_LRU_DEPRIO) {
	nr_lru_sort_tried_cold_regions = s->stat.nr_tried;
	bytes_lru_sort_tried_cold_regions = s->stat.sz_tried;
	nr_lru_sorted_cold_regions = s->stat.nr_applied;
	bytes_lru_sorted_cold_regions = s->stat.sz_applied;
	nr_cold_quota_exceeds = s->stat.qt_exceeds;
	}
	}

	return damon_lru_sort_handle_commit_inputs();
	}

	static int damon_lru_sort_after_wmarks_check(struct damon_ctx *c)
	{
	return damon_lru_sort_handle_commit_inputs();
	}

	static int __init damon_lru_sort_init(void)
	{
	ctx = damon_new_ctx();
	if (!ctx)
	return -ENOMEM;

	if (damon_select_ops(ctx, DAMON_OPS_PADDR)) {
	damon_destroy_ctx(ctx);
	return -EINVAL;
	}

	ctx->callback.after_wmarks_check = damon_lru_sort_after_wmarks_check;
	ctx->callback.after_aggregation = damon_lru_sort_after_aggregation;

	target = damon_new_target();
	if (!target) {
	damon_destroy_ctx(ctx);
	return -ENOMEM;
	}
	damon_add_target(ctx, target);

	schedule_delayed_work(&damon_lru_sort_timer, 0);

	damon_lru_sort_initialized = true;
	return 0;
	}

	module_init(damon_lru_sort_init);