On Mon, 24 Feb 2020 13:30:41 +0100
SeongJae Park <sjpark@xxxxxxxxxx> wrote:
> From: SeongJae Park <sjpark@xxxxxxxxx>
>
> This commit adds a debugfs interface for DAMON.
>
> 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 starts the monitoring.
>
> Record
> ------
>
> DAMON support 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 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@xxxxxxxxx>
Some of the code in here seems a bit fragile and convoluted.
> ---
> mm/damon.c | 377 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 376 insertions(+), 1 deletion(-)
>
> diff --git a/mm/damon.c b/mm/damon.c
> index b3e9b9da5720..facb1d7f121b 100644
> --- a/mm/damon.c
> +++ b/mm/damon.c
> @@ -10,6 +10,7 @@
> #define pr_fmt(fmt) "damon: " fmt
>
> #include <linux/damon.h>
> +#include <linux/debugfs.h>
> #include <linux/delay.h>
> #include <linux/kthread.h>
> #include <linux/mm.h>
> @@ -46,6 +47,24 @@
> /* Get a random number in [l, r) */
> #define damon_rand(ctx, l, r) (l + prandom_u32_state(&ctx->rndseed) % (r - l))
>
> +/*
> + * For each 'sample_interval', DAMON checks whether each region is accessed or
> + * not. It aggregates and keeps the access information (number of accesses to
> + * each region) for 'aggr_interval' and then flushes it to the result buffer if
> + * an 'aggr_interval' surpassed. And for each 'regions_update_interval', damon
> + * checks whether the memory mapping of the target tasks has changed (e.g., by
> + * mmap() calls from the applications) and applies the changes.
> + *
> + * All time intervals are in micro-seconds.
> + */
> +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,
> +};
> +
> /*
> * Construct a damon_region struct
> *
> @@ -1026,15 +1045,371 @@ int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
> return 0;
> }
>
> +/*
> + * debugfs functions
Seems unnecessary when their naming makes this clear.
> + */
> +
> +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 ret;
> +
> + spin_lock(&ctx->kdamond_lock);
> + monitor_on = ctx->kdamond != NULL;
> + spin_unlock(&ctx->kdamond_lock);
> +
> + ret = snprintf(monitor_on_buf, 5, monitor_on ? "on\n" : "off\n");
> +
> + return simple_read_from_buffer(buf, count, ppos, monitor_on_buf, ret);
> +}
> +
> +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;
> + 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(ctx, on))
> + return -EINVAL;
> +
> + 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(ctx, t) {
> + rc = snprintf(&buf[written], len - written, "%lu ", 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];
> +
> + len = damon_sprint_pids(ctx, pids_buf, 320);
> + 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 unsigned long *str_to_pids(const char *str, ssize_t len,
> + ssize_t *nr_pids)
> +{
> + unsigned long *pids;
> + const int max_nr_pids = 32;
> + unsigned long pid;
> + int pos = 0, parsed, ret;
> +
> + *nr_pids = 0;
> + pids = kmalloc_array(max_nr_pids, sizeof(unsigned long), GFP_KERNEL);
> + if (!pids)
> + return NULL;
> + while (*nr_pids < max_nr_pids && 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)
> +{
> + struct damon_ctx *ctx = &damon_user_ctx;
> + char *kbuf;
> + unsigned long *targets;
> + ssize_t nr_targets;
> + ssize_t ret;
> +
> + kbuf = kmalloc_array(count, sizeof(char), GFP_KERNEL);
> + if (!kbuf)
> + return -ENOMEM;
> +
> + ret = simple_write_to_buffer(kbuf, 512, ppos, buf, count);
Why only 512?
> + if (ret < 0)
> + goto out;
> +
> + targets = str_to_pids(kbuf, ret, &nr_targets);
> + if (!targets) {
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + spin_lock(&ctx->kdamond_lock);
> + if (ctx->kdamond)
> + goto monitor_running;
> +
> + damon_set_pids(ctx, targets, nr_targets);
> + spin_unlock(&ctx->kdamond_lock);
> +
> + goto free_targets_out;
> +
> +monitor_running:
> + spin_unlock(&ctx->kdamond_lock);
> + pr_err("%s: kdamond is running. Turn it off first.\n", __func__);
> + ret = -EINVAL;
> +free_targets_out:
> + 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;
> +
> + ret = snprintf(record_buf, ARRAY_SIZE(record_buf), "%u %s\n",
> + ctx->rbuf_len, ctx->rfile_path);
> + 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;
> +
> + kbuf = kmalloc_array(count + 1, sizeof(char), GFP_KERNEL);
> + if (!kbuf)
> + return -ENOMEM;
> + kbuf[count] = '\0';
> +
> + ret = simple_write_to_buffer(kbuf, count, ppos, buf, count);
> + if (ret < 0)
> + goto out;
> + if (sscanf(kbuf, "%u %s",
> + &rbuf_len, rfile_path) != 2) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + spin_lock(&ctx->kdamond_lock);
> + if (ctx->kdamond)
> + goto monitor_running;
> +
> + damon_set_recording(ctx, rbuf_len, rfile_path);
> + spin_unlock(&ctx->kdamond_lock);
> +
> + goto out;
> +
> +monitor_running:
> + spin_unlock(&ctx->kdamond_lock);
> + pr_err("%s: kdamond is running. Turn it off first.\n", __func__);
> + ret = -EINVAL;
> +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;
> +
> + 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);
> +
> + 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;
> +
> + kbuf = kmalloc_array(count, sizeof(char), GFP_KERNEL);
malloc fine for array of characters. The checks on overflow etc cannot be
relevant here.
> + if (!kbuf)
> + return -ENOMEM;
> +
> + ret = simple_write_to_buffer(kbuf, count, ppos, buf, count);
> + if (ret < 0)
> + goto out;
> +
> + if (sscanf(kbuf, "%lu %lu %lu %lu %lu",
> + &s, &a, &r, &minr, &maxr) != 5) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + spin_lock(&ctx->kdamond_lock);
> + if (ctx->kdamond)
> + goto monitor_running;
> +
> + damon_set_attrs(ctx, s, a, r, minr, maxr);
> + spin_unlock(&ctx->kdamond_lock);
> +
> + goto out;
> +
> +monitor_running:
> + spin_unlock(&ctx->kdamond_lock);
> + pr_err("%s: kdamond is running. Turn it off first.\n", __func__);
> + ret = -EINVAL;
This complex exit path is a bad idea from maintainability point of view...
Just put the pr_err and spin_unlock in the error path above.
> +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 debugfs_init(void)
Prefix this function. Chances of sometime getting a header
that includes debugfs_init feels rather too high!
> +{
> + 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;
> +
> + ctx->rbuf_offset = 0;
> + rc = damon_set_recording(ctx, 1024 * 1024, "/damon.data");
> + if (rc)
> + return rc;
> +
> + ctx->kdamond = NULL;
> + ctx->kdamond_stop = false;
> + spin_lock_init(&ctx->kdamond_lock);
> +
> + prandom_seed_state(&ctx->rndseed, 42);
:)
> + INIT_LIST_HEAD(&ctx->tasks_list);
> +
> + ctx->sample_cb = NULL;
> + ctx->aggregate_cb = NULL;
Should already be set to 0.
> +
> + return 0;
> +}
> +
> static int __init damon_init(void)
> {
> + int rc;
> +
> pr_info("init\n");
>
> - return 0;
> + rc = damon_init_user_ctx();
> + if (rc)
> + return rc;
> +
> + return debugfs_init();
In theory no code should ever be dependent on debugfs succeeding..
There might be other daemon users so you should just eat the return
code.
> }
>
> static void __exit damon_exit(void)
> {
> + damon_turn_kdamond(&damon_user_ctx, false);
> + debugfs_remove_recursive(debugfs_root);
> +
> + kfree(damon_user_ctx.rbuf);
> + kfree(damon_user_ctx.rfile_path);
> +
> pr_info("exit\n");
> }
>
