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

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

#include <linux/damon.h>
#include <linux/kstrtox.h>
#include <linux/module.h>

#include "modules-common.h"

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

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

/*
 * Make DAMON_RECLAIM reads the input parameters again, except ``enabled``.
 *
 * Input parameters that updated while DAMON_RECLAIM is running are not applied
 * by default.  Once this parameter is set as ``Y``, DAMON_RECLAIM reads values
 * of parameters 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_RECLAIM will be disabled.
 */
static bool commit_inputs __read_mostly;
module_param(commit_inputs, bool, 0600);

/*
 * Time threshold for cold memory regions identification in microseconds.
 *
 * If a memory region is not accessed for this or longer time, DAMON_RECLAIM
 * identifies the region as cold, and reclaims.  120 seconds by default.
 */
static unsigned long min_age __read_mostly = 120000000;
module_param(min_age, ulong, 0600);

static struct damos_quota damon_reclaim_quota = {
        /* use up to 10 ms time, reclaim up to 128 MiB per 1 sec by default */
        .ms = 10,
        .sz = 128 * 1024 * 1024,
        .reset_interval = 1000,
        /* Within the quota, page out older regions first. */
        .weight_sz = 0,
        .weight_nr_accesses = 0,
        .weight_age = 1
};
DEFINE_DAMON_MODULES_DAMOS_QUOTAS(damon_reclaim_quota);

/*
 * Desired level of memory pressure-stall time in microseconds.
 *
 * While keeping the caps that set by other quotas, DAMON_RECLAIM automatically
 * increases and decreases the effective level of the quota aiming this level of
 * memory pressure is incurred.  System-wide ``some`` memory PSI in microseconds
 * per quota reset interval (``quota_reset_interval_ms``) is collected and
 * compared to this value to see if the aim is satisfied.  Value zero means
 * disabling this auto-tuning feature.
 *
 * Disabled by default.
 */
static unsigned long quota_mem_pressure_us __read_mostly;
module_param(quota_mem_pressure_us, ulong, 0600);

/*
 * User-specifiable feedback for auto-tuning of the effective quota.
 *
 * While keeping the caps that set by other quotas, DAMON_RECLAIM automatically
 * increases and decreases the effective level of the quota aiming receiving this
 * feedback of value ``10,000`` from the user.  DAMON_RECLAIM assumes the feedback
 * value and the quota are positively proportional.  Value zero means disabling
 * this auto-tuning feature.
 *
 * Disabled by default.
 *
 */
static unsigned long quota_autotune_feedback __read_mostly;
module_param(quota_autotune_feedback, ulong, 0600);

static struct damos_watermarks damon_reclaim_wmarks = {
        .metric = DAMOS_WMARK_FREE_MEM_RATE,
        .interval = 5000000,    /* 5 seconds */
        .high = 500,            /* 50 percent */
        .mid = 400,             /* 40 percent */
        .low = 200,             /* 20 percent */
};
DEFINE_DAMON_MODULES_WMARKS_PARAMS(damon_reclaim_wmarks);

static struct damon_attrs damon_reclaim_mon_attrs = {
        .sample_interval = 5000,        /* 5 ms */
        .aggr_interval = 100000,        /* 100 ms */
        .ops_update_interval = 0,
        .min_nr_regions = 10,
        .max_nr_regions = 1000,
};
DEFINE_DAMON_MODULES_MON_ATTRS_PARAMS(damon_reclaim_mon_attrs);

/*
 * Start of the target memory region in physical address.
 *
 * The start physical address of memory region that DAMON_RECLAIM 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_RECLAIM 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);

/*
 * Scale factor for DAMON_RECLAIM to ops address conversion.
 *
 * This parameter must not be set to 0.
 */
static unsigned long addr_unit __read_mostly = 1;

/*
 * Skip anonymous pages reclamation.
 *
 * If this parameter is set as ``Y``, DAMON_RECLAIM does not reclaim anonymous
 * pages.  By default, ``N``.
 */
static bool skip_anon __read_mostly;
module_param(skip_anon, bool, 0600);

/*
 * PID of the DAMON thread
 *
 * If DAMON_RECLAIM 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);

static struct damos_stat damon_reclaim_stat;
DEFINE_DAMON_MODULES_DAMOS_STATS_PARAMS(damon_reclaim_stat,
                reclaim_tried_regions, reclaimed_regions, quota_exceeds);

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

static struct damos *damon_reclaim_new_scheme(void)
{
        struct damos_access_pattern pattern = {
                /* Find regions having PAGE_SIZE or larger size */
                .min_sz_region = PAGE_SIZE,
                .max_sz_region = ULONG_MAX,
                /* and not accessed at all */
                .min_nr_accesses = 0,
                .max_nr_accesses = 0,
                /* for min_age or more micro-seconds */
                .min_age_region = min_age /
                        damon_reclaim_mon_attrs.aggr_interval,
                .max_age_region = UINT_MAX,
        };

        return damon_new_scheme(
                        &pattern,
                        /* page out those, as soon as found */
                        DAMOS_PAGEOUT,
                        /* for each aggregation interval */
                        0,
                        /* under the quota. */
                        &damon_reclaim_quota,
                        /* (De)activate this according to the watermarks. */
                        &damon_reclaim_wmarks,
                        NUMA_NO_NODE);
}

static int damon_reclaim_apply_parameters(void)
{
        struct damon_ctx *param_ctx;
        struct damon_target *param_target;
        struct damos *scheme;
        struct damos_quota_goal *goal;
        struct damos_filter *filter;
        int err;

        err = damon_modules_new_paddr_ctx_target(&param_ctx, &param_target);
        if (err)
                return err;

        /*
         * If monitor_region_start/end are unset, always silently
         * reset addr_unit to 1.
         */
        if (!monitor_region_start && !monitor_region_end)
                addr_unit = 1;
        param_ctx->addr_unit = addr_unit;
        param_ctx->min_region_sz = max(DAMON_MIN_REGION_SZ / addr_unit, 1);

        if (!damon_reclaim_mon_attrs.aggr_interval) {
                err = -EINVAL;
                goto out;
        }

        err = damon_set_attrs(param_ctx, &damon_reclaim_mon_attrs);
        if (err)
                goto out;

        err = -ENOMEM;
        scheme = damon_reclaim_new_scheme();
        if (!scheme)
                goto out;
        damon_set_schemes(param_ctx, &scheme, 1);

        if (quota_mem_pressure_us) {
                goal = damos_new_quota_goal(DAMOS_QUOTA_SOME_MEM_PSI_US,
                                quota_mem_pressure_us);
                if (!goal)
                        goto out;
                damos_add_quota_goal(&scheme->quota, goal);
        }

        if (quota_autotune_feedback) {
                goal = damos_new_quota_goal(DAMOS_QUOTA_USER_INPUT, 10000);
                if (!goal)
                        goto out;
                goal->current_value = quota_autotune_feedback;
                damos_add_quota_goal(&scheme->quota, goal);
        }

        if (skip_anon) {
                filter = damos_new_filter(DAMOS_FILTER_TYPE_ANON, true, false);
                if (!filter)
                        goto out;
                damos_add_filter(scheme, filter);
        }

        err = damon_set_region_biggest_system_ram_default(param_target,
                                        &monitor_region_start,
                                        &monitor_region_end,
                                        param_ctx->min_region_sz);
        if (err)
                goto out;
        err = damon_commit_ctx(ctx, param_ctx);
out:
        damon_destroy_ctx(param_ctx);
        return err;
}

static int damon_reclaim_handle_commit_inputs(void)
{
        int err;

        if (!commit_inputs)
                return 0;

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

static int damon_reclaim_damon_call_fn(void *arg)
{
        struct damon_ctx *c = arg;
        struct damos *s;

        /* update the stats parameter */
        damon_for_each_scheme(s, c)
                damon_reclaim_stat = s->stat;

        return damon_reclaim_handle_commit_inputs();
}

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

static int damon_reclaim_turn(bool on)
{
        int err;

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

        err = damon_reclaim_apply_parameters();
        if (err)
                return err;

        err = damon_start(&ctx, 1, true);
        if (err)
                return err;
        kdamond_pid = damon_kdamond_pid(ctx);
        if (kdamond_pid < 0)
                return kdamond_pid;
        return damon_call(ctx, &call_control);
}

static int damon_reclaim_addr_unit_store(const char *val,
                const struct kernel_param *kp)
{
        unsigned long input_addr_unit;
        int err = kstrtoul(val, 0, &input_addr_unit);

        if (err)
                return err;
        if (!input_addr_unit)
                return -EINVAL;

        addr_unit = input_addr_unit;
        return 0;
}

static const struct kernel_param_ops addr_unit_param_ops = {
        .set = damon_reclaim_addr_unit_store,
        .get = param_get_ulong,
};

module_param_cb(addr_unit, &addr_unit_param_ops, &addr_unit, 0600);
MODULE_PARM_DESC(addr_unit,
        "Scale factor for DAMON_RECLAIM to ops address conversion (default: 1)");

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

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

        if (is_enabled == enable)
                return 0;

        /* Called before init function.  The function will handle this. */
        if (!damon_initialized())
                goto set_param_out;

        err = damon_reclaim_turn(enable);
        if (err)
                return err;

set_param_out:
        enabled = enable;
        return err;
}

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

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

static int __init damon_reclaim_init(void)
{
        int err;

        if (!damon_initialized()) {
                err = -ENOMEM;
                goto out;
        }
        err = damon_modules_new_paddr_ctx_target(&ctx, &target);
        if (err)
                goto out;

        call_control.data = ctx;

        /* 'enabled' has set before this function, probably via command line */
        if (enabled)
                err = damon_reclaim_turn(true);

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

module_init(damon_reclaim_init);