3 files changed, 163 insertions, 0 deletions
diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
index c93d0c56b96390..b3171f9406c18b 100644
--- a/mm/damon/Kconfig
+++ b/mm/damon/Kconfig
@@ -94,4 +94,20 @@ config DAMON_LRU_SORT
 	  protect frequently accessed (hot) pages while rarely accessed (cold)
 	  pages reclaimed first under memory pressure.
 
+config DAMON_STAT
+	bool "Build data access monitoring stat (DAMON_STAT)"
+	depends on DAMON_PADDR
+	help
+	  This builds the DAMON-based access monitoring statistics subsystem.
+	  It runs DAMON and expose access monitoring results in simple stat
+	  metrics.
+
+config DAMON_STAT_ENABLED_DEFAULT
+	bool "Enable DAMON_STAT by default"
+	depends on DAMON_PADDR
+	default DAMON_STAT
+	help
+	  Whether to enable DAMON_STAT by default.  Users can disable it in
+	  boot or runtime using its 'enabled' parameter.
+
 endmenu
diff --git a/mm/damon/Makefile b/mm/damon/Makefile
index 8b49012ba8c304..d8d6bf5f8bff4e 100644
--- a/mm/damon/Makefile
+++ b/mm/damon/Makefile
@@ -6,3 +6,4 @@ obj-$(CONFIG_DAMON_PADDR)	+= ops-common.o paddr.o
 obj-$(CONFIG_DAMON_SYSFS)	+= sysfs-common.o sysfs-schemes.o sysfs.o
 obj-$(CONFIG_DAMON_RECLAIM)	+= modules-common.o reclaim.o
 obj-$(CONFIG_DAMON_LRU_SORT)	+= modules-common.o lru_sort.o
+obj-$(CONFIG_DAMON_STAT)	+= modules-common.o stat.o
diff --git a/mm/damon/stat.c b/mm/damon/stat.c
new file mode 100644
index 00000000000000..dd00f2384b9579
--- /dev/null
+++ b/mm/damon/stat.c
@@ -0,0 +1,146 @@
+// 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 struct damon_ctx *damon_stat_context;
+
+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 int damon_stat_start(void)
+{
+	damon_stat_context = damon_stat_build_ctx();
+	if (!damon_stat_context)
+		return -ENOMEM;
+	return damon_start(&damon_stat_context, 1, true);
+}
+
+static void damon_stat_stop(void)
+{
+	damon_stop(&damon_stat_context, 1);
+	damon_destroy_ctx(damon_stat_context);
+}
+
+static bool damon_stat_init_called;
+
+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_stat_init_called)
+		/*
+		 * 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;
+
+	damon_stat_init_called = true;
+
+	/* probably set via command line */
+	if (enabled)
+		err = damon_stat_start();
+
+	if (err && enabled)
+		enabled = false;
+	return err;
+}
+
+module_init(damon_stat_init);