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Subject[RFC PATCH 2/5] mm/damon: Add debugfs interface
Date
From: SeongJae Park <sjpark@amazon.de>

This commit adds a debugfs interface for DAMON.

DAMON exports three files, ``attrs``, ``pids``, and ``monitor_on`` under
its debugfs directory, ``<debugfs>/damon/``.

Attributes
----------

Users can read and write the ``sampling interval``, ``aggregation
interval``, ``regions update interval``, min/max number of regions, and
the path to ``result file`` by reading from and writing to the ``attrs``
file. For example, below commands set those values to 5 ms, 100 ms,
1,000 ms, 10, 1000, and ``/damon.data`` and check it again::

# cd <debugfs>/damon
# echo 5000 100000 1000000 10 1000 /damon.data > attrs
# cat attrs
5000 100000 1000000 10 1000 /damon.data

Target PIDs
-----------

Users can read and write the pids of current monitoring target processes
by reading from and writing to the `pids` file. For example, below
commands set processes having pids 42 and 4242 as the processes to be
monitored and check it again::

# cd <debugfs>/damon
# echo 42 4242 > pids
# cat pids
42 4242

Note that setting the pids doesn't starts the monitoring.

Turning On/Off
--------------

You can check current status, start and stop the monitoring by reading
from and writing to the ``monitor_on`` file. Writing ``on`` to the file
starts DAMON to monitor the target processes with the attributes.
Writing ``off`` to the file stops DAMON. DAMON also stops if every
target processes is be terminated. Below example commands turn on, off,
and check status of DAMON::

# cd <debugfs>/damon
# echo on > monitor_on
# echo off > monitor_on
# cat monitor_on
off

Please note that you cannot write to the ``attrs`` and ``pids`` files
while the monitoring is turned on. If you write to the files while
DAMON is running, ``-EINVAL`` will be returned.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
mm/damon.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 228 insertions(+), 1 deletion(-)

diff --git a/mm/damon.c b/mm/damon.c
index 9a603c3f966a..0e99b4875700 100644
--- a/mm/damon.c
+++ b/mm/damon.c
@@ -9,6 +9,7 @@

#define pr_fmt(fmt) "damon: " fmt

+#include <linux/debugfs.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/mm.h>
@@ -1023,6 +1024,232 @@ static long damon_set_attrs(unsigned long sample_int,
return 0;
}

+/*
+ * debugfs functions
+ */
+
+static ssize_t debugfs_monitor_on_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ char monitor_on_buf[5];
+ bool monitor_on;
+
+ spin_lock(&kdamond_lock);
+ monitor_on = kdamond != NULL;
+ spin_unlock(&kdamond_lock);
+
+ snprintf(monitor_on_buf, 5, monitor_on ? "on\n" : "off\n");
+
+ return simple_read_from_buffer(buf, count, ppos, monitor_on_buf,
+ monitor_on ? 3 : 4);
+}
+
+static ssize_t debugfs_monitor_on_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ ssize_t ret;
+ bool on = false;
+ char cmdbuf[5];
+
+ ret = simple_write_to_buffer(cmdbuf, 5, ppos, buf, count);
+ if (ret < 0)
+ return ret;
+
+ if (sscanf(cmdbuf, "%s", cmdbuf) != 1)
+ return -EINVAL;
+ if (!strncmp(cmdbuf, "on", 5))
+ on = true;
+ else if (!strncmp(cmdbuf, "off", 5))
+ on = false;
+ else
+ return -EINVAL;
+
+ if (damon_turn_kdamond(on))
+ return -EINVAL;
+
+ return ret;
+}
+
+static ssize_t damon_sprint_pids(char *buf, ssize_t len)
+{
+ char *cursor = buf;
+ struct damon_task *t;
+
+ damon_for_each_task(t) {
+ snprintf(cursor, len, "%lu ", t->pid);
+ cursor += strnlen(cursor, len);
+ }
+ if (cursor != buf)
+ cursor--;
+ snprintf(cursor, len, "\n");
+ return strnlen(buf, len);
+}
+
+static ssize_t debugfs_pids_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ ssize_t len;
+ char pids_buf[512];
+
+ len = damon_sprint_pids(pids_buf, 512);
+
+ return simple_read_from_buffer(buf, count, ppos, pids_buf, len);
+}
+
+/*
+ * Converts a string into an array of unsigned long integers
+ *
+ * Returns an array of unsigned long integers that converted, or NULL if the
+ * input is wrong.
+ */
+static unsigned long *str_to_pids(const char *str, ssize_t len,
+ ssize_t *nr_pids)
+{
+ unsigned long *pids;
+ unsigned long pid;
+ int pos = 0, parsed, ret;
+
+ *nr_pids = 0;
+ pids = kmalloc_array(256, sizeof(unsigned long), GFP_KERNEL);
+ while (*nr_pids < 256 && pos < len) {
+ ret = sscanf(&str[pos], "%lu%n", &pid, &parsed);
+ pos += parsed;
+ if (ret != 1)
+ break;
+ pids[*nr_pids] = pid;
+ *nr_pids += 1;
+ }
+ if (*nr_pids == 0) {
+ kfree(pids);
+ pids = NULL;
+ }
+
+ return pids;
+}
+
+static ssize_t debugfs_pids_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ ssize_t ret;
+ unsigned long *targets;
+ ssize_t nr_targets;
+ char pids_buf[512];
+
+ ret = simple_write_to_buffer(pids_buf, 512, ppos, buf, count);
+ if (ret < 0)
+ return ret;
+
+ targets = str_to_pids(pids_buf, ret, &nr_targets);
+
+ spin_lock(&kdamond_lock);
+ if (kdamond)
+ goto monitor_running;
+
+ damon_set_pids(targets, nr_targets);
+ spin_unlock(&kdamond_lock);
+ kfree(targets);
+
+ return ret;
+
+monitor_running:
+ spin_unlock(&kdamond_lock);
+ pr_err("%s: kdamond is running. Turn it off first.\n", __func__);
+ return -EINVAL;
+}
+
+static ssize_t debugfs_attrs_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ char attrs_buf[512];
+
+ snprintf(attrs_buf, 512, "%lu %lu %lu %lu %lu %s\n",
+ sample_interval, aggr_interval,
+ regions_update_interval, min_nr_regions,
+ max_nr_regions, rfile_path);
+
+ return simple_read_from_buffer(buf, count, ppos, attrs_buf,
+ strnlen(attrs_buf, 512));
+}
+
+static ssize_t debugfs_attrs_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ unsigned long s, a, r, minr, maxr;
+ char attrs_buf[512];
+ char res_file_path[LEN_RES_FILE_PATH];
+ ssize_t ret;
+
+ if (count > 512) {
+ pr_err("attributes stream is too large: %s\n", buf);
+ return -ENOMEM;
+ }
+
+ ret = simple_write_to_buffer(attrs_buf, 512, ppos, buf, count);
+ if (ret < 0)
+ return ret;
+
+ if (sscanf(attrs_buf, "%lu %lu %lu %lu %lu %s",
+ &s, &a, &r, &minr, &maxr, res_file_path) != 6)
+ return -EINVAL;
+
+ spin_lock(&kdamond_lock);
+ if (kdamond)
+ goto monitor_running;
+
+ damon_set_attrs(s, a, r, minr, maxr, res_file_path);
+ spin_unlock(&kdamond_lock);
+
+ return ret;
+
+monitor_running:
+ spin_unlock(&kdamond_lock);
+ pr_err("%s: kdamond is running. Turn it off first.\n", __func__);
+ return -EINVAL;
+}
+
+static const struct file_operations monitor_on_fops = {
+ .owner = THIS_MODULE,
+ .read = debugfs_monitor_on_read,
+ .write = debugfs_monitor_on_write,
+};
+
+static const struct file_operations pids_fops = {
+ .owner = THIS_MODULE,
+ .read = debugfs_pids_read,
+ .write = debugfs_pids_write,
+};
+
+static const struct file_operations attrs_fops = {
+ .owner = THIS_MODULE,
+ .read = debugfs_attrs_read,
+ .write = debugfs_attrs_write,
+};
+
+static int __init debugfs_init(void)
+{
+ struct dentry *debugfs_root;
+ const char * const file_names[] = {"attrs", "pids", "monitor_on"};
+ const struct file_operations *fops[] = {&attrs_fops, &pids_fops,
+ &monitor_on_fops};
+ int i;
+
+ debugfs_root = debugfs_create_dir("damon", NULL);
+ if (!debugfs_root) {
+ pr_err("failed to create the debugfs dir\n");
+ return -ENOMEM;
+ }
+
+ for (i = 0; i < ARRAY_SIZE(file_names); i++) {
+ if (!debugfs_create_file(file_names[i], 0600, debugfs_root,
+ NULL, fops[i])) {
+ pr_err("failed to create %s file\n", file_names[i]);
+ return -ENOMEM;
+ }
+ }
+
+ return 0;
+}
+
static int __init damon_init(void)
{
pr_info("init\n");
@@ -1031,7 +1258,7 @@ static int __init damon_init(void)
ktime_get_coarse_ts64(&last_aggregate_time);
last_regions_update_time = last_aggregate_time;

- return 0;
+ return debugfs_init();
}

module_init(damon_init);
--
2.17.1
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