[PATCH v18 09/14] mm/damon: Implement a debugfs interface

SeongJae Park
2020-07-13T08:45:35Z

From: SeongJae Park <sjpark@amazon.de>

This commit implements a debugfs interface for DAMON. It works for the
virtual address spaces monitoring.

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

Attributes
----------

Users can read and write the ``sampling interval``, ``aggregation
interval``, ``regions update interval``, and min/max number of
monitoring target regions 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 check it again::

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

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 start the monitoring.

Record
------

DAMON supports direct monitoring result record feature. The recorded
results are first written to a buffer and flushed to a file in batch.
Users can set the size of the buffer and the path to the result file by
reading from and writing to the ``record`` file. For example, below
commands set the buffer to be 4 KiB and the result to be saved in
'/damon.data'.

# cd <debugfs>/damon
# echo 4096 /damon.data > pids
# cat record
4096 /damon.data

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 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>
Reviewed-by: Leonard Foerster <foersleo@amazon.de>
---
mm/damon.c | 381 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 380 insertions(+), 1 deletion(-)

diff --git a/mm/damon.c b/mm/damon.c
index 00df1a4c3d5c..df05bd821ff8 100644
--- a/mm/damon.c
+++ b/mm/damon.c
@@ -14,6 +14,7 @@
* - Functions for the access checking of the regions
* - Functions for DAMON core logics and features
* - Functions for the DAMON programming interface
+ * - Functions for the DAMON debugfs interface
* - Functions for the module loading/unloading
*/

@@ -22,6 +23,7 @@
#define CREATE_TRACE_POINTS

#include <linux/damon.h>
+#include <linux/debugfs.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/mm.h>
@@ -68,6 +70,20 @@
/* Get a random number in [l, r) */
#define damon_rand(l, r) (l + prandom_u32() % (r - l))

+/* A monitoring context for debugfs interface users. */
+static struct damon_ctx damon_user_ctx = {
+ .sample_interval = 5 * 1000,
+ .aggr_interval = 100 * 1000,
+ .regions_update_interval = 1000 * 1000,
+ .min_nr_regions = 10,
+ .max_nr_regions = 1000,
+
+ .init_target_regions = kdamond_init_vm_regions,
+ .update_target_regions = kdamond_update_vm_regions,
+ .prepare_access_checks = kdamond_prepare_vm_access_checks,
+ .check_accesses = kdamond_check_vm_accesses,
+};
+
/*
* Construct a damon_region struct
*
@@ -1228,17 +1244,380 @@ int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
return 0;
}

+/*
+ * Functions for the DAMON debugfs interface
+ */
+
+static ssize_t debugfs_monitor_on_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ char monitor_on_buf[5];
+ bool monitor_on;
+ int len;
+
+ monitor_on = damon_kdamond_running(ctx);
+ len = snprintf(monitor_on_buf, 5, monitor_on ? "on\n" : "off\n");
+
+ return simple_read_from_buffer(buf, count, ppos, monitor_on_buf, len);
+}
+
+/*
+ * Returns non-empty string on success, negarive error code otherwise.
+ */
+static char *user_input_str(const char __user *buf, size_t count, loff_t *ppos)
+{
+ char *kbuf;
+ ssize_t ret;
+
+ /* We do not accept continuous write */
+ if (*ppos)
+ return ERR_PTR(-EINVAL);
+
+ kbuf = kmalloc(count + 1, GFP_KERNEL);
+ if (!kbuf)
+ return ERR_PTR(-ENOMEM);
+
+ ret = simple_write_to_buffer(kbuf, count + 1, ppos, buf, count);
+ if (ret != count) {
+ kfree(kbuf);
+ return ERR_PTR(-EIO);
+ }
+ kbuf[ret] = '\0';
+
+ return kbuf;
+}
+
+static ssize_t debugfs_monitor_on_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ ssize_t ret = count;
+ char *kbuf;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ /* Remove white space */
+ if (sscanf(kbuf, "%s", kbuf) != 1)
+ return -EINVAL;
+ if (!strncmp(kbuf, "on", count))
+ err = damon_start(ctx);
+ else if (!strncmp(kbuf, "off", count))
+ err = damon_stop(ctx);
+ else
+ return -EINVAL;
+
+ if (err)
+ ret = err;
+ return ret;
+}
+
+static ssize_t damon_sprint_pids(struct damon_ctx *ctx, char *buf, ssize_t len)
+{
+ struct damon_task *t;
+ int written = 0;
+ int rc;
+
+ damon_for_each_task(t, ctx) {
+ rc = snprintf(&buf[written], len - written, "%d ", t->pid);
+ if (!rc)
+ return -ENOMEM;
+ written += rc;
+ }
+ if (written)
+ written -= 1;
+ written += snprintf(&buf[written], len - written, "\n");
+ return written;
+}
+
+static ssize_t debugfs_pids_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ ssize_t len;
+ char pids_buf[320];
+
+ mutex_lock(&ctx->kdamond_lock);
+ len = damon_sprint_pids(ctx, pids_buf, 320);
+ mutex_unlock(&ctx->kdamond_lock);
+ if (len < 0)
+ return len;
+
+ 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 if the conversion success, or
+ * NULL otherwise.
+ */
+static int *str_to_pids(const char *str, ssize_t len, ssize_t *nr_pids)
+{
+ int *pids;
+ const int max_nr_pids = 32;
+ int pid;
+ int pos = 0, parsed, ret;
+
+ *nr_pids = 0;
+ pids = kmalloc_array(max_nr_pids, sizeof(pid), GFP_KERNEL);
+ if (!pids)
+ return NULL;
+ while (*nr_pids < max_nr_pids && pos < len) {
+ ret = sscanf(&str[pos], "%d%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)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ char *kbuf;
+ int *targets;
+ ssize_t nr_targets;
+ ssize_t ret = count;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ targets = str_to_pids(kbuf, ret, &nr_targets);
+ if (!targets) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ mutex_lock(&ctx->kdamond_lock);
+ if (ctx->kdamond) {
+ ret = -EINVAL;
+ goto unlock_out;
+ }
+
+ err = damon_set_pids(ctx, targets, nr_targets);
+ if (err)
+ ret = err;
+unlock_out:
+ mutex_unlock(&ctx->kdamond_lock);
+ kfree(targets);
+out:
+ kfree(kbuf);
+ return ret;
+}
+
+static ssize_t debugfs_record_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ char record_buf[20 + MAX_RFILE_PATH_LEN];
+ int ret;
+
+ mutex_lock(&ctx->kdamond_lock);
+ ret = snprintf(record_buf, ARRAY_SIZE(record_buf), "%u %s\n",
+ ctx->rbuf_len, ctx->rfile_path);
+ mutex_unlock(&ctx->kdamond_lock);
+ return simple_read_from_buffer(buf, count, ppos, record_buf, ret);
+}
+
+static ssize_t debugfs_record_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ char *kbuf;
+ unsigned int rbuf_len;
+ char rfile_path[MAX_RFILE_PATH_LEN];
+ ssize_t ret = count;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ if (sscanf(kbuf, "%u %s",
+ &rbuf_len, rfile_path) != 2) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ mutex_lock(&ctx->kdamond_lock);
+ if (ctx->kdamond) {
+ ret = -EBUSY;
+ goto unlock_out;
+ }
+
+ err = damon_set_recording(ctx, rbuf_len, rfile_path);
+ if (err)
+ ret = err;
+unlock_out:
+ mutex_unlock(&ctx->kdamond_lock);
+out:
+ kfree(kbuf);
+ return ret;
+}
+
+static ssize_t debugfs_attrs_read(struct file *file,
+ char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ char kbuf[128];
+ int ret;
+
+ mutex_lock(&ctx->kdamond_lock);
+ ret = snprintf(kbuf, ARRAY_SIZE(kbuf), "%lu %lu %lu %lu %lu\n",
+ ctx->sample_interval, ctx->aggr_interval,
+ ctx->regions_update_interval, ctx->min_nr_regions,
+ ctx->max_nr_regions);
+ mutex_unlock(&ctx->kdamond_lock);
+
+ return simple_read_from_buffer(buf, count, ppos, kbuf, ret);
+}
+
+static ssize_t debugfs_attrs_write(struct file *file,
+ const char __user *buf, size_t count, loff_t *ppos)
+{
+ struct damon_ctx *ctx = &damon_user_ctx;
+ unsigned long s, a, r, minr, maxr;
+ char *kbuf;
+ ssize_t ret = count;
+ int err;
+
+ kbuf = user_input_str(buf, count, ppos);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ if (sscanf(kbuf, "%lu %lu %lu %lu %lu",
+ &s, &a, &r, &minr, &maxr) != 5) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ mutex_lock(&ctx->kdamond_lock);
+ if (ctx->kdamond) {
+ ret = -EBUSY;
+ goto unlock_out;
+ }
+
+ err = damon_set_attrs(ctx, s, a, r, minr, maxr);
+ if (err)
+ ret = err;
+unlock_out:
+ mutex_unlock(&ctx->kdamond_lock);
+out:
+ kfree(kbuf);
+ return ret;
+}
+
+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 record_fops = {
+ .owner = THIS_MODULE,
+ .read = debugfs_record_read,
+ .write = debugfs_record_write,
+};
+
+static const struct file_operations attrs_fops = {
+ .owner = THIS_MODULE,
+ .read = debugfs_attrs_read,
+ .write = debugfs_attrs_write,
+};
+
+static struct dentry *debugfs_root;
+
+static int __init damon_debugfs_init(void)
+{
+ const char * const file_names[] = {"attrs", "record",
+ "pids", "monitor_on"};
+ const struct file_operations *fops[] = {&attrs_fops, &record_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_user_ctx(void)
+{
+ int rc;
+
+ struct damon_ctx *ctx = &damon_user_ctx;
+
+ ktime_get_coarse_ts64(&ctx->last_aggregation);
+ ctx->last_regions_update = ctx->last_aggregation;
+
+ rc = damon_set_recording(ctx, 1024 * 1024, "/damon.data");
+ if (rc)
+ return rc;
+
+ mutex_init(&ctx->kdamond_lock);
+
+ INIT_LIST_HEAD(&ctx->tasks_list);
+
+ return 0;
+}
+
/*
* Functions for the module loading/unloading
*/

static int __init damon_init(void)
{
- return 0;
+ int rc;
+
+ rc = damon_init_user_ctx();
+ if (rc)
+ return rc;
+
+ rc = damon_debugfs_init();
+ if (rc)
+ pr_err("%s: debugfs init failed\n", __func__);
+
+ return rc;
}

static void __exit damon_exit(void)
{
+ damon_stop(&damon_user_ctx);
+ debugfs_remove_recursive(debugfs_root);
+
+ kfree(damon_user_ctx.rbuf);
+ kfree(damon_user_ctx.rfile_path);
}

module_init(damon_init);
--
2.17.1