--- /dev/null
+// 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/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_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;
+module_param(enabled, 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);
+
+/*
+ * Limit of time for trying the reclamation in milliseconds.
+ *
+ * DAMON_RECLAIM tries to use only up to this time within a time window
+ * (quota_reset_interval_ms) for trying reclamation of cold pages. This can be
+ * used for limiting CPU consumption of DAMON_RECLAIM. 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);
+
+/*
+ * Limit of size of memory for the reclamation in bytes.
+ *
+ * DAMON_RECLAIM charges amount of memory which it tried to reclaim within a
+ * time window (quota_reset_interval_ms) and makes no more than this limit is
+ * tried. This can be used for limiting consumption of CPU and IO. If this
+ * value is zero, the limit is disabled.
+ *
+ * 128 MiB by default.
+ */
+static unsigned long quota_sz __read_mostly = 128 * 1024 * 1024;
+module_param(quota_sz, ulong, 0600);
+
+/*
+ * The time/size quota charge reset interval in milliseconds.
+ *
+ * The charge reset interval for the quota of time (quota_ms) and size
+ * (quota_sz). That is, DAMON_RECLAIM does not try reclamation 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_RECLAIM 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_RECLAIM becomes inactive, so it does nothing but periodically
+ * checks the watermarks. 500 (50%) by default.
+ */
+static unsigned long wmarks_high __read_mostly = 500;
+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_RECLAIM becomes active, so starts the monitoring
+ * and the reclaiming. 400 (40%) by default.
+ */
+static unsigned long wmarks_mid __read_mostly = 400;
+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_RECLAIM becomes inactive, so it does nothing but periodically checks
+ * the watermarks. In the case, the system falls back to the LRU-based page
+ * granularity reclamation logic. 200 (20%) by default.
+ */
+static unsigned long wmarks_low __read_mostly = 200;
+module_param(wmarks_low, ulong, 0600);
+
+/*
+ * Sampling interval for the monitoring in microseconds.
+ *
+ * The sampling interval of DAMON for the 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 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 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 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_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);
+
+/*
+ * 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 damon_ctx *ctx;
+static struct damon_target *target;
+
+struct damon_reclaim_ram_walk_arg {
+ unsigned long start;
+ unsigned long end;
+};
+
+static int walk_system_ram(struct resource *res, void *arg)
+{
+ struct damon_reclaim_ram_walk_arg *a = arg;
+
+ if (a->end - a->start < res->end - res->start) {
+ 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_reclaim_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;
+}
+
+static struct damos *damon_reclaim_new_scheme(void)
+{
+ 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 reclamation for more than quota_ms milliseconds
+ * or quota_sz bytes within quota_reset_interval_ms.
+ */
+ .ms = quota_ms,
+ .sz = quota_sz,
+ .reset_interval = quota_reset_interval_ms,
+ /* Within the quota, page out older regions 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 min_age or more micro-seconds, and */
+ min_age / aggr_interval, UINT_MAX,
+ /* page out those, as soon as found */
+ DAMOS_PAGEOUT,
+ /* under the quota. */
+ "a,
+ /* (De)activate this according to the watermarks. */
+ &wmarks);
+
+ return scheme;
+}
+
+static int damon_reclaim_turn(bool on)
+{
+ struct damon_region *region;
+ struct damos *scheme;
+ int err;
+
+ if (!on) {
+ err = damon_stop(&ctx, 1);
+ if (!err)
+ kdamond_pid = -1;
+ return err;
+ }
+
+ err = damon_set_attrs(ctx, sample_interval, aggr_interval, 0,
+ min_nr_regions, max_nr_regions);
+ if (err)
+ return err;
+
+ 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;
+ /* DAMON will free this on its own when finish monitoring */
+ region = damon_new_region(monitor_region_start, monitor_region_end);
+ if (!region)
+ return -ENOMEM;
+ damon_add_region(region, target);
+
+ /* Will be freed by 'damon_set_schemes()' below */
+ scheme = damon_reclaim_new_scheme();
+ if (!scheme) {
+ err = -ENOMEM;
+ goto free_region_out;
+ }
+ err = damon_set_schemes(ctx, &scheme, 1);
+ if (err)
+ goto free_scheme_out;
+
+ err = damon_start(&ctx, 1);
+ if (!err) {
+ kdamond_pid = ctx->kdamond->pid;
+ return 0;
+ }
+
+free_scheme_out:
+ damon_destroy_scheme(scheme);
+free_region_out:
+ damon_destroy_region(region, target);
+ return err;
+}
+
+#define ENABLE_CHECK_INTERVAL_MS 1000
+static struct delayed_work damon_reclaim_timer;
+static void damon_reclaim_timer_fn(struct work_struct *work)
+{
+ static bool last_enabled;
+ bool now_enabled;
+
+ now_enabled = enabled;
+ if (last_enabled != now_enabled) {
+ if (!damon_reclaim_turn(now_enabled))
+ last_enabled = now_enabled;
+ else
+ enabled = last_enabled;
+ }
+
+ schedule_delayed_work(&damon_reclaim_timer,
+ msecs_to_jiffies(ENABLE_CHECK_INTERVAL_MS));
+}
+static DECLARE_DELAYED_WORK(damon_reclaim_timer, damon_reclaim_timer_fn);
+
+static int __init damon_reclaim_init(void)
+{
+ ctx = damon_new_ctx();
+ if (!ctx)
+ return -ENOMEM;
+
+ damon_pa_set_primitives(ctx);
+
+ /* 4242 means nothing but fun */
+ target = damon_new_target(4242);
+ if (!target) {
+ damon_destroy_ctx(ctx);
+ return -ENOMEM;
+ }
+ damon_add_target(ctx, target);
+
+ schedule_delayed_work(&damon_reclaim_timer, 0);
+ return 0;
+}
+
+module_init(damon_reclaim_init);
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