Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

5 files changed, 631 insertions, 0 deletions

diff --git a/samples/damon/Kconfig b/samples/damon/Kconfig
new file mode 100644
index 000000000..00be3e6bd
--- /dev/null
+++ b/samples/damon/Kconfig
@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menu "DAMON Samples"
+
+config SAMPLE_DAMON_WSSE
+	bool "DAMON sample module for working set size estimation"
+	depends on DAMON && DAMON_VADDR
+	help
+	  This builds DAMON sample module for working set size estimation.
+
+	  The module receives a pid, monitor access to the virtual address
+	  space of the process, estimate working set size of the process, and
+	  repeatedly prints the size on the kernel log.
+
+	  If unsure, say N.
+
+config SAMPLE_DAMON_PRCL
+	bool "DAMON sample module for access-aware proactive reclamation"
+	depends on DAMON && DAMON_VADDR
+	help
+	  This builds DAMON sample module for access-aware proactive
+	  reclamation.
+
+	  The module receives a pid, monitor access to the virtual address
+	  space of the process, find memory regions that not accessed, and
+	  proactively reclaim the regions.
+
+	  If unsure, say N.
+
+config SAMPLE_DAMON_MTIER
+	bool "DAMON sample module for memory tiering"
+	depends on DAMON && DAMON_PADDR
+	help
+	  This builds DAMON sample module for memory tiering.
+
+	  The module assumes the system is constructed with two NUMA nodes,
+	  which seems as local and remote nodes to all CPUs.  For example,
+	  node0 is for DDR5 DRAMs connected via DIMM, while node1 is for DDR4
+	  DRAMs connected via CXL.
+
+	  If unsure, say N.
+
+endmenu
diff --git a/samples/damon/Makefile b/samples/damon/Makefile
new file mode 100644
index 000000000..72f68cbf4
--- /dev/null
+++ b/samples/damon/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_SAMPLE_DAMON_WSSE) += wsse.o
+obj-$(CONFIG_SAMPLE_DAMON_PRCL) += prcl.o
+obj-$(CONFIG_SAMPLE_DAMON_MTIER) += mtier.o
diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c
new file mode 100644
index 000000000..d1123ebbf
--- /dev/null
+++ b/samples/damon/mtier.c
@@ -0,0 +1,255 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * memory tiering: migrate cold pages in node 0 and hot pages in node 1 to node
+ * 1 and node 0, respectively.  Adjust the hotness/coldness threshold aiming
+ * resulting 99.6 % node 0 utilization ratio.
+ */
+
+#define pr_fmt(fmt) "damon_sample_mtier: " fmt
+
+#include <linux/damon.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "damon_sample_mtier."
+
+static unsigned long node0_start_addr __read_mostly;
+module_param(node0_start_addr, ulong, 0600);
+
+static unsigned long node0_end_addr __read_mostly;
+module_param(node0_end_addr, ulong, 0600);
+
+static unsigned long node1_start_addr __read_mostly;
+module_param(node1_start_addr, ulong, 0600);
+
+static unsigned long node1_end_addr __read_mostly;
+module_param(node1_end_addr, ulong, 0600);
+
+static unsigned long node0_mem_used_bp __read_mostly = 9970;
+module_param(node0_mem_used_bp, ulong, 0600);
+
+static unsigned long node0_mem_free_bp __read_mostly = 50;
+module_param(node0_mem_free_bp, ulong, 0600);
+
+static int damon_sample_mtier_enable_store(
+		const char *val, const struct kernel_param *kp);
+
+static const struct kernel_param_ops enabled_param_ops = {
+	.set = damon_sample_mtier_enable_store,
+	.get = param_get_bool,
+};
+
+static bool enabled __read_mostly;
+module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
+MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_MTIER");
+
+static bool detect_node_addresses __read_mostly;
+module_param(detect_node_addresses, bool, 0600);
+
+static struct damon_ctx *ctxs[2];
+
+struct region_range {
+	phys_addr_t start;
+	phys_addr_t end;
+};
+
+static int nid_to_phys(int target_node, struct region_range *range)
+{
+	if (!node_online(target_node)) {
+		pr_err("NUMA node %d is not online\n", target_node);
+		return -EINVAL;
+	}
+
+	range->start = PFN_PHYS(node_start_pfn(target_node));
+	range->end  = PFN_PHYS(node_end_pfn(target_node));
+
+	return 0;
+}
+
+static struct damon_ctx *damon_sample_mtier_build_ctx(bool promote)
+{
+	struct damon_ctx *ctx;
+	struct damon_attrs attrs;
+	struct damon_target *target;
+	struct damos *scheme;
+	struct damos_quota_goal *quota_goal;
+	struct damos_filter *filter;
+	struct region_range addr;
+	struct damon_addr_range range;
+	int ret;
+
+	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;
+	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 (detect_node_addresses) {
+		ret = promote ? nid_to_phys(1, &addr) : nid_to_phys(0, &addr);
+		if (ret)
+			goto free_out;
+	} else {
+		addr.start = promote ? node1_start_addr : node0_start_addr;
+		addr.end = promote ? node1_end_addr : node0_end_addr;
+	}
+
+	if (addr.start >= addr.end)
+		goto free_out;
+
+	range.start = addr.start;
+	range.end = addr.end;
+
+	ret = damon_set_regions(target, &range, 1, DAMON_MIN_REGION_SZ);
+	if (ret)
+		goto free_out;
+
+	scheme = damon_new_scheme(
+			/* access pattern */
+			&(struct damos_access_pattern) {
+				.min_sz_region = PAGE_SIZE,
+				.max_sz_region = ULONG_MAX,
+				.min_nr_accesses = promote ? 1 : 0,
+				.max_nr_accesses = promote ? UINT_MAX : 0,
+				.min_age_region = 0,
+				.max_age_region = UINT_MAX},
+			/* action */
+			promote ? DAMOS_MIGRATE_HOT : DAMOS_MIGRATE_COLD,
+			1000000,	/* apply interval (1s) */
+			&(struct damos_quota){
+				/* 200 MiB per sec by most */
+				.reset_interval = 1000,
+				.sz = 200 * 1024 * 1024,
+				/* ignore size of region when prioritizing */
+				.weight_sz = 0,
+				.weight_nr_accesses = 100,
+				.weight_age = 100,
+			},
+			&(struct damos_watermarks){},
+			promote ? 0 : 1);	/* migrate target node id */
+	if (!scheme)
+		goto free_out;
+	damon_set_schemes(ctx, &scheme, 1);
+	/* zero target value causes division by zero in damos_quota_store() */
+	if (!node0_mem_used_bp || !node0_mem_free_bp)
+		goto free_out;
+	quota_goal = damos_new_quota_goal(
+			promote ? DAMOS_QUOTA_NODE_MEM_USED_BP :
+			DAMOS_QUOTA_NODE_MEM_FREE_BP,
+			promote ? node0_mem_used_bp : node0_mem_free_bp);
+	if (!quota_goal)
+		goto free_out;
+	quota_goal->nid = 0;
+	damos_add_quota_goal(&scheme->quota, quota_goal);
+	filter = damos_new_filter(DAMOS_FILTER_TYPE_YOUNG, true, promote);
+	if (!filter)
+		goto free_out;
+	damos_add_filter(scheme, filter);
+	return ctx;
+free_out:
+	damon_destroy_ctx(ctx);
+	return NULL;
+}
+
+static int damon_sample_mtier_start(void)
+{
+	struct damon_ctx *ctx;
+	int err;
+
+	ctx = damon_sample_mtier_build_ctx(true);
+	if (!ctx)
+		return -ENOMEM;
+	ctxs[0] = ctx;
+	ctx = damon_sample_mtier_build_ctx(false);
+	if (!ctx) {
+		damon_destroy_ctx(ctxs[0]);
+		return -ENOMEM;
+	}
+	ctxs[1] = ctx;
+	err = damon_start(ctxs, 2, true);
+	if (!err)
+		return 0;
+
+	damon_destroy_ctx(ctxs[0]);
+	damon_destroy_ctx(ctxs[1]);
+	return err;
+}
+
+static void damon_sample_mtier_stop(void)
+{
+	damon_stop(ctxs, 2);
+	damon_destroy_ctx(ctxs[0]);
+	damon_destroy_ctx(ctxs[1]);
+}
+
+static int damon_sample_mtier_enable_store(
+		const char *val, const struct kernel_param *kp)
+{
+	bool is_enabled = enabled;
+	int err;
+
+	err = kstrtobool(val, &enabled);
+	if (err)
+		return err;
+
+	if (enabled == is_enabled)
+		return 0;
+
+	if (!damon_initialized())
+		return 0;
+
+	if (enabled) {
+		err = damon_sample_mtier_start();
+		if (err)
+			enabled = false;
+		return err;
+	}
+	damon_sample_mtier_stop();
+	return 0;
+}
+
+static int __init damon_sample_mtier_init(void)
+{
+	int err = 0;
+
+	if (!damon_initialized()) {
+		if (enabled)
+			enabled = false;
+		return -ENOMEM;
+	}
+
+	if (enabled) {
+		err = damon_sample_mtier_start();
+		if (err)
+			enabled = false;
+	}
+	return 0;
+}
+
+module_init(damon_sample_mtier_init);
diff --git a/samples/damon/prcl.c b/samples/damon/prcl.c
new file mode 100644
index 000000000..842099bd6
--- /dev/null
+++ b/samples/damon/prcl.c
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * proactive reclamation: monitor access pattern of a given process, find
+ * regions that seems not accessed, and proactively page out the regions.
+ */
+
+#define pr_fmt(fmt) "damon_sample_prcl: " fmt
+
+#include <linux/damon.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "damon_sample_prcl."
+
+static int target_pid __read_mostly;
+module_param(target_pid, int, 0600);
+
+static int damon_sample_prcl_enable_store(
+		const char *val, const struct kernel_param *kp);
+
+static const struct kernel_param_ops enabled_param_ops = {
+	.set = damon_sample_prcl_enable_store,
+	.get = param_get_bool,
+};
+
+static bool enabled __read_mostly;
+module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
+MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_PRCL");
+
+static struct damon_ctx *ctx;
+static struct pid *target_pidp;
+
+static int damon_sample_prcl_repeat_call_fn(void *data)
+{
+	struct damon_ctx *c = data;
+	struct damon_target *t;
+
+	damon_for_each_target(t, c) {
+		struct damon_region *r;
+		unsigned long wss = 0;
+
+		damon_for_each_region(r, t) {
+			if (r->nr_accesses > 0)
+				wss += r->ar.end - r->ar.start;
+		}
+		pr_info("wss: %lu\n", wss);
+	}
+	return 0;
+}
+
+static struct damon_call_control repeat_call_control = {
+	.fn = damon_sample_prcl_repeat_call_fn,
+	.repeat = true,
+};
+
+static int damon_sample_prcl_start(void)
+{
+	struct damon_target *target;
+	struct damos *scheme;
+	int err;
+
+	pr_info("start\n");
+
+	ctx = damon_new_ctx();
+	if (!ctx)
+		return -ENOMEM;
+	if (damon_select_ops(ctx, DAMON_OPS_VADDR)) {
+		damon_destroy_ctx(ctx);
+		return -EINVAL;
+	}
+
+	target = damon_new_target();
+	if (!target) {
+		damon_destroy_ctx(ctx);
+		return -ENOMEM;
+	}
+	damon_add_target(ctx, target);
+	target_pidp = find_get_pid(target_pid);
+	if (!target_pidp) {
+		damon_destroy_ctx(ctx);
+		return -EINVAL;
+	}
+	target->pid = target_pidp;
+
+	scheme = damon_new_scheme(
+			&(struct damos_access_pattern) {
+			.min_sz_region = PAGE_SIZE,
+			.max_sz_region = ULONG_MAX,
+			.min_nr_accesses = 0,
+			.max_nr_accesses = 0,
+			.min_age_region = 50,
+			.max_age_region = UINT_MAX},
+			DAMOS_PAGEOUT,
+			0,
+			&(struct damos_quota){},
+			&(struct damos_watermarks){},
+			NUMA_NO_NODE);
+	if (!scheme) {
+		damon_destroy_ctx(ctx);
+		return -ENOMEM;
+	}
+	damon_set_schemes(ctx, &scheme, 1);
+
+	err = damon_start(&ctx, 1, true);
+	if (err) {
+		damon_destroy_ctx(ctx);
+		return err;
+	}
+
+	repeat_call_control.data = ctx;
+	err = damon_call(ctx, &repeat_call_control);
+	if (err)
+		damon_destroy_ctx(ctx);
+	return err;
+}
+
+static void damon_sample_prcl_stop(void)
+{
+	pr_info("stop\n");
+	if (ctx) {
+		damon_stop(&ctx, 1);
+		damon_destroy_ctx(ctx);
+	}
+}
+
+static int damon_sample_prcl_enable_store(
+		const char *val, const struct kernel_param *kp)
+{
+	bool is_enabled = enabled;
+	int err;
+
+	err = kstrtobool(val, &enabled);
+	if (err)
+		return err;
+
+	if (enabled == is_enabled)
+		return 0;
+
+	if (!damon_initialized())
+		return 0;
+
+	if (enabled) {
+		err = damon_sample_prcl_start();
+		if (err)
+			enabled = false;
+		return err;
+	}
+	damon_sample_prcl_stop();
+	return 0;
+}
+
+static int __init damon_sample_prcl_init(void)
+{
+	int err = 0;
+
+	if (!damon_initialized()) {
+		if (enabled)
+			enabled = false;
+		return -ENOMEM;
+	}
+
+	if (enabled) {
+		err = damon_sample_prcl_start();
+		if (err)
+			enabled = false;
+	}
+	return 0;
+}
+
+module_init(damon_sample_prcl_init);
diff --git a/samples/damon/wsse.c b/samples/damon/wsse.c
new file mode 100644
index 000000000..37fd5da20
--- /dev/null
+++ b/samples/damon/wsse.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * working set size estimation: monitor access pattern of given process and
+ * print estimated working set size (total size of regions that showing some
+ * access).
+ */
+
+#define pr_fmt(fmt) "damon_sample_wsse: " fmt
+
+#include <linux/damon.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "damon_sample_wsse."
+
+static int target_pid __read_mostly;
+module_param(target_pid, int, 0600);
+
+static int damon_sample_wsse_enable_store(
+		const char *val, const struct kernel_param *kp);
+
+static const struct kernel_param_ops enabled_param_ops = {
+	.set = damon_sample_wsse_enable_store,
+	.get = param_get_bool,
+};
+
+static bool enabled __read_mostly;
+module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
+MODULE_PARM_DESC(enabled, "Enable or disable DAMON_SAMPLE_WSSE");
+
+static struct damon_ctx *ctx;
+static struct pid *target_pidp;
+
+static int damon_sample_wsse_repeat_call_fn(void *data)
+{
+	struct damon_ctx *c = data;
+	struct damon_target *t;
+
+	damon_for_each_target(t, c) {
+		struct damon_region *r;
+		unsigned long wss = 0;
+
+		damon_for_each_region(r, t) {
+			if (r->nr_accesses > 0)
+				wss += r->ar.end - r->ar.start;
+		}
+		pr_info("wss: %lu\n", wss);
+	}
+	return 0;
+}
+
+static struct damon_call_control repeat_call_control = {
+	.fn = damon_sample_wsse_repeat_call_fn,
+	.repeat = true,
+};
+
+static int damon_sample_wsse_start(void)
+{
+	struct damon_target *target;
+	int err;
+
+	pr_info("start\n");
+
+	ctx = damon_new_ctx();
+	if (!ctx)
+		return -ENOMEM;
+	if (damon_select_ops(ctx, DAMON_OPS_VADDR)) {
+		damon_destroy_ctx(ctx);
+		return -EINVAL;
+	}
+
+	target = damon_new_target();
+	if (!target) {
+		damon_destroy_ctx(ctx);
+		return -ENOMEM;
+	}
+	damon_add_target(ctx, target);
+	target_pidp = find_get_pid(target_pid);
+	if (!target_pidp) {
+		damon_destroy_ctx(ctx);
+		return -EINVAL;
+	}
+	target->pid = target_pidp;
+
+	err = damon_start(&ctx, 1, true);
+	if (err) {
+		damon_destroy_ctx(ctx);
+		return err;
+	}
+	repeat_call_control.data = ctx;
+	err = damon_call(ctx, &repeat_call_control);
+	if (err)
+		damon_destroy_ctx(ctx);
+	return err;
+}
+
+static void damon_sample_wsse_stop(void)
+{
+	pr_info("stop\n");
+	if (ctx) {
+		damon_stop(&ctx, 1);
+		damon_destroy_ctx(ctx);
+	}
+}
+
+static int damon_sample_wsse_enable_store(
+		const char *val, const struct kernel_param *kp)
+{
+	bool is_enabled = enabled;
+	int err;
+
+	err = kstrtobool(val, &enabled);
+	if (err)
+		return err;
+
+	if (enabled == is_enabled)
+		return 0;
+
+	if (!damon_initialized())
+		return 0;
+
+	if (enabled) {
+		err = damon_sample_wsse_start();
+		if (err)
+			enabled = false;
+		return err;
+	}
+	damon_sample_wsse_stop();
+	return 0;
+}
+
+static int __init damon_sample_wsse_init(void)
+{
+	int err = 0;
+
+	if (!damon_initialized()) {
+		err = -ENOMEM;
+		if (enabled)
+			enabled = false;
+	}
+
+	if (enabled) {
+		err = damon_sample_wsse_start();
+		if (err)
+			enabled = false;
+	}
+	return err;
+}
+
+module_init(damon_sample_wsse_init);