Re: [PATCH v23 07/15] mm/damon: Implement a debugfs-based user space interface

[Shakeel Butt]

On Tue, Dec 15, 2020 at 3:59 AM SeongJae Park <sjpark@xxxxxxxxxx> wrote:
>
> From: SeongJae Park <sjpark@xxxxxxxxx>
>
> DAMON is designed to be used by kernel space code such as the memory
> management subsystems, and therefore it provides only kernel space API.

Which kernel space APIs are being referred here?

> That said, letting the user space control DAMON could provide some
> benefits to them.  For example, it will allow user space to analyze
> their specific workloads and make their own special optimizations.
>
> For such cases, this commit implements a simple DAMON application kernel
> module, namely 'damon-dbgfs', which merely wraps the DAMON api and
> exports those to the user space via the debugfs.
>
> 'damon-dbgfs' exports three files, ``attrs``, ``target_ids``, 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 IDs
> ----------
>
> Some types of address spaces supports multiple monitoring target.  For
> example, the virtual memory address spaces monitoring can have multiple
> processes as the monitoring targets.  Users can set the targets by
> writing relevant id values of the targets to, and get the ids of the
> current targets by reading from the ``target_ids`` file.  In case of the
> virtual address spaces monitoring, the values should be pids of the
> monitoring target processes.  For example, below commands set processes
> having pids 42 and 4242 as the monitoring targets and check it again::
>
>     # cd <debugfs>/damon
>     # echo 42 4242 > target_ids
>     # cat target_ids
>     42 4242
>
> Note that setting the target ids doesn't start the monitoring.
>
> Turning On/Off
> --------------
>
> Setting the files as described above doesn't incur effect unless you
> explicitly start the monitoring.  You can start, stop, and check the
> current status of the monitoring by writing to and reading from the
> ``monitor_on`` file.  Writing ``on`` to the file starts the monitoring
> of the targets with the attributes.  Writing ``off`` to the file stops
> those.  DAMON also stops if every targets are invalidated (in case of
> the virtual memory monitoring, target processes are invalidated when
> terminated).  Below example commands turn on, off, and check the 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 above-mentioned debugfs files
> while the monitoring is turned on.  If you write to the files while
> DAMON is running, an error code such as ``-EBUSY`` will be returned.
>
> Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
> Reviewed-by: Leonard Foerster <foersleo@xxxxxxxxx>
> ---
>  include/linux/damon.h |   3 +
>  mm/damon/Kconfig      |   9 ++
>  mm/damon/Makefile     |   1 +
>  mm/damon/core.c       |  45 ++++++
>  mm/damon/dbgfs.c      | 366 ++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 424 insertions(+)
>  create mode 100644 mm/damon/dbgfs.c
>
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 39b4d6d3ddee..f9e0d4349352 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -265,9 +265,12 @@ unsigned int damon_nr_regions(struct damon_target *t);
>
>  struct damon_ctx *damon_new_ctx(enum damon_target_type type);
>  void damon_destroy_ctx(struct damon_ctx *ctx);
> +int damon_set_targets(struct damon_ctx *ctx,
> +               unsigned long *ids, ssize_t nr_ids);
>  int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
>                 unsigned long aggr_int, unsigned long regions_update_int,
>                 unsigned long min_nr_reg, unsigned long max_nr_reg);
> +int damon_nr_running_ctxs(void);
>
>  int damon_start(struct damon_ctx **ctxs, int nr_ctxs);
>  int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
> diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
> index 8ae080c52950..72f1683ba0ee 100644
> --- a/mm/damon/Kconfig
> +++ b/mm/damon/Kconfig
> @@ -21,4 +21,13 @@ config DAMON_VADDR
>           This builds the default data access monitoring primitives for DAMON
>           that works for virtual address spaces.
>
> +config DAMON_DBGFS
> +       bool "DAMON debugfs interface"
> +       depends on DAMON_VADDR && DEBUG_FS
> +       help
> +         This builds the debugfs interface for DAMON.  The user space admins
> +         can use the interface for arbitrary data access monitoring.
> +
> +         If unsure, say N.
> +
>  endmenu
> diff --git a/mm/damon/Makefile b/mm/damon/Makefile
> index 6ebbd08aed67..fed4be3bace3 100644
> --- a/mm/damon/Makefile
> +++ b/mm/damon/Makefile
> @@ -2,3 +2,4 @@
>
>  obj-$(CONFIG_DAMON)            := core.o
>  obj-$(CONFIG_DAMON_VADDR)      += vaddr.o
> +obj-$(CONFIG_DAMON_DBGFS)      += dbgfs.o
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 5ca9f79ccbb6..b9575a6bebff 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -166,6 +166,37 @@ void damon_destroy_ctx(struct damon_ctx *ctx)
>         kfree(ctx);
>  }
>
> +/**
> + * damon_set_targets() - Set monitoring targets.
> + * @ctx:       monitoring context
> + * @ids:       array of target ids
> + * @nr_ids:    number of entries in @ids
> + *
> + * This function should not be called while the kdamond is running.
> + *
> + * Return: 0 on success, negative error code otherwise.
> + */
> +int damon_set_targets(struct damon_ctx *ctx,
> +                     unsigned long *ids, ssize_t nr_ids)
> +{
> +       ssize_t i;
> +       struct damon_target *t, *next;
> +
> +       damon_for_each_target_safe(t, next, ctx)
> +               damon_destroy_target(t);

You need to put the reference on the target before destroying.

> +
> +       for (i = 0; i < nr_ids; i++) {
> +               t = damon_new_target(ids[i]);
> +               if (!t) {
> +                       pr_err("Failed to alloc damon_target\n");
> +                       return -ENOMEM;
> +               }
> +               damon_add_target(ctx, t);
> +       }
> +
> +       return 0;
> +}
> +
>  /**
>   * damon_set_attrs() - Set attributes for the monitoring.
>   * @ctx:               monitoring context
> @@ -206,6 +237,20 @@ int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
>         return 0;
>  }
>
> +/**
> + * damon_nr_running_ctxs() - Return number of currently running contexts.
> + */
> +int damon_nr_running_ctxs(void)
> +{
> +       int nr_ctxs;
> +
> +       mutex_lock(&damon_lock);
> +       nr_ctxs = nr_running_ctxs;
> +       mutex_unlock(&damon_lock);

READ_ONCE(nr_running_ctxs) ?

> +
> +       return nr_ctxs;
> +}
> +
>  /* Returns the size upper limit for each monitoring region */
>  static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
>  {
> diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
> new file mode 100644
> index 000000000000..fd1665a183c2
> --- /dev/null
> +++ b/mm/damon/dbgfs.c
> @@ -0,0 +1,366 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * DAMON Debugfs Interface
> + *
> + * Author: SeongJae Park <sjpark@xxxxxxxxx>
> + */
> +
> +#define pr_fmt(fmt) "damon-dbgfs: " fmt
> +
> +#include <linux/damon.h>
> +#include <linux/debugfs.h>
> +#include <linux/file.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/page_idle.h>
> +#include <linux/slab.h>
> +
> +static struct damon_ctx **dbgfs_ctxs;
> +static int dbgfs_nr_ctxs;
> +static struct dentry **dbgfs_dirs;
> +
> +/*
> + * 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 dbgfs_attrs_read(struct file *file,
> +               char __user *buf, size_t count, loff_t *ppos)
> +{
> +       struct damon_ctx *ctx = file->private_data;
> +       char kbuf[128];
> +       int ret;
> +
> +       mutex_lock(&ctx->kdamond_lock);
> +       ret = scnprintf(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 dbgfs_attrs_write(struct file *file,
> +               const char __user *buf, size_t count, loff_t *ppos)
> +{
> +       struct damon_ctx *ctx = file->private_data;
> +       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;
> +}
> +
> +#define targetid_is_pid(ctx)   \
> +       (ctx->primitive.target_valid == damon_va_target_valid)
> +
> +static ssize_t sprint_target_ids(struct damon_ctx *ctx, char *buf, ssize_t len)
> +{
> +       struct damon_target *t;
> +       unsigned long id;
> +       int written = 0;
> +       int rc;
> +
> +       damon_for_each_target(t, ctx) {
> +               id = t->id;
> +               if (targetid_is_pid(ctx))
> +                       /* Show pid numbers to debugfs users */
> +                       id = (unsigned long)pid_vnr((struct pid *)id);
> +
> +               rc = scnprintf(&buf[written], len - written, "%lu ", id);
> +               if (!rc)
> +                       return -ENOMEM;
> +               written += rc;
> +       }
> +       if (written)
> +               written -= 1;
> +       written += scnprintf(&buf[written], len - written, "\n");
> +       return written;
> +}
> +
> +static ssize_t dbgfs_target_ids_read(struct file *file,
> +               char __user *buf, size_t count, loff_t *ppos)
> +{
> +       struct damon_ctx *ctx = file->private_data;
> +       ssize_t len;
> +       char ids_buf[320];
> +
> +       mutex_lock(&ctx->kdamond_lock);
> +       len = sprint_target_ids(ctx, ids_buf, 320);
> +       mutex_unlock(&ctx->kdamond_lock);
> +       if (len < 0)
> +               return len;
> +
> +       return simple_read_from_buffer(buf, count, ppos, ids_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_target_ids(const char *str, ssize_t len,
> +                                       ssize_t *nr_ids)
> +{
> +       unsigned long *ids;
> +       const int max_nr_ids = 32;
> +       unsigned long id;
> +       int pos = 0, parsed, ret;
> +
> +       *nr_ids = 0;
> +       ids = kmalloc_array(max_nr_ids, sizeof(id), GFP_KERNEL);
> +       if (!ids)
> +               return NULL;
> +       while (*nr_ids < max_nr_ids && pos < len) {
> +               ret = sscanf(&str[pos], "%lu%n", &id, &parsed);
> +               pos += parsed;
> +               if (ret != 1)
> +                       break;
> +               ids[*nr_ids] = id;
> +               *nr_ids += 1;
> +       }
> +
> +       return ids;
> +}
> +
> +static ssize_t dbgfs_target_ids_write(struct file *file,
> +               const char __user *buf, size_t count, loff_t *ppos)
> +{
> +       struct damon_ctx *ctx = file->private_data;
> +       char *kbuf, *nrs;
> +       unsigned long *targets;
> +       ssize_t nr_targets;
> +       ssize_t ret = count;
> +       int i;
> +       int err;
> +
> +       kbuf = user_input_str(buf, count, ppos);
> +       if (IS_ERR(kbuf))
> +               return PTR_ERR(kbuf);
> +
> +       nrs = kbuf;
> +
> +       targets = str_to_target_ids(nrs, ret, &nr_targets);
> +       if (!targets) {
> +               ret = -ENOMEM;
> +               goto out;
> +       }
> +
> +       if (targetid_is_pid(ctx)) {
> +               for (i = 0; i < nr_targets; i++)
> +                       targets[i] = (unsigned long)find_get_pid(
> +                                       (int)targets[i]);
> +       }
> +
> +       mutex_lock(&ctx->kdamond_lock);
> +       if (ctx->kdamond) {
> +               ret = -EINVAL;
> +               goto unlock_out;

You need to put_pid on the targets array.

> +       }
> +
> +       err = damon_set_targets(ctx, targets, nr_targets);
> +       if (err)
> +               ret = err;

You need to handle the partial failure from damon_set_targets().


> +unlock_out:
> +       mutex_unlock(&ctx->kdamond_lock);
> +       kfree(targets);
> +out:
> +       kfree(kbuf);
> +       return ret;
> +}
> +
> +static int damon_dbgfs_open(struct inode *inode, struct file *file)
> +{
> +       file->private_data = inode->i_private;
> +
> +       return nonseekable_open(inode, file);
> +}
> +
> +static const struct file_operations attrs_fops = {
> +       .owner = THIS_MODULE,
> +       .open = damon_dbgfs_open,
> +       .read = dbgfs_attrs_read,
> +       .write = dbgfs_attrs_write,
> +};
> +
> +static const struct file_operations target_ids_fops = {
> +       .owner = THIS_MODULE,
> +       .open = damon_dbgfs_open,
> +       .read = dbgfs_target_ids_read,
> +       .write = dbgfs_target_ids_write,
> +};
> +
> +static int dbgfs_fill_ctx_dir(struct dentry *dir, struct damon_ctx *ctx)
> +{
> +       const char * const file_names[] = {"attrs", "target_ids"};
> +       const struct file_operations *fops[] = {&attrs_fops, &target_ids_fops};
> +       int i;
> +
> +       for (i = 0; i < ARRAY_SIZE(file_names); i++) {
> +               if (!debugfs_create_file(file_names[i], 0600, dir,
> +                                       ctx, fops[i])) {
> +                       pr_err("failed to create %s file\n", file_names[i]);
> +                       return -ENOMEM;
> +               }
> +       }
> +
> +       return 0;
> +}
> +
> +static struct damon_ctx *dbgfs_new_ctx(void)
> +{
> +       struct damon_ctx *ctx;
> +
> +       ctx = damon_new_ctx(DAMON_ADAPTIVE_TARGET);
> +       if (!ctx)
> +               return NULL;
> +
> +       damon_va_set_primitives(ctx);
> +       return ctx;
> +}
> +
> +static ssize_t dbgfs_monitor_on_read(struct file *file,
> +               char __user *buf, size_t count, loff_t *ppos)
> +{
> +       char monitor_on_buf[5];
> +       bool monitor_on = damon_nr_running_ctxs() != 0;
> +       int len;
> +
> +       len = scnprintf(monitor_on_buf, 5, monitor_on ? "on\n" : "off\n");
> +
> +       return simple_read_from_buffer(buf, count, ppos, monitor_on_buf, len);
> +}
> +
> +static ssize_t dbgfs_monitor_on_write(struct file *file,
> +               const char __user *buf, size_t count, loff_t *ppos)
> +{
> +       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) {
> +               kfree(kbuf);
> +               return -EINVAL;
> +       }
> +
> +       if (!strncmp(kbuf, "on", count))
> +               err = damon_start(dbgfs_ctxs, dbgfs_nr_ctxs);
> +       else if (!strncmp(kbuf, "off", count))
> +               err = damon_stop(dbgfs_ctxs, dbgfs_nr_ctxs);
> +       else
> +               err = -EINVAL;
> +
> +       if (err)
> +               ret = err;
> +       kfree(kbuf);
> +       return ret;
> +}
> +
> +static const struct file_operations monitor_on_fops = {
> +       .owner = THIS_MODULE,
> +       .read = dbgfs_monitor_on_read,
> +       .write = dbgfs_monitor_on_write,
> +};
> +
> +static int __init __damon_dbgfs_init(void)
> +{
> +       struct dentry *dbgfs_root;
> +       const char * const file_names[] = {"monitor_on"};
> +       const struct file_operations *fops[] = {&monitor_on_fops};
> +       int i;
> +
> +       dbgfs_root = debugfs_create_dir("damon", NULL);
> +       if (IS_ERR(dbgfs_root)) {
> +               pr_err("failed to create the dbgfs dir\n");
> +               return PTR_ERR(dbgfs_root);
> +       }
> +
> +       for (i = 0; i < ARRAY_SIZE(file_names); i++) {
> +               if (!debugfs_create_file(file_names[i], 0600, dbgfs_root,
> +                                       NULL, fops[i])) {
> +                       pr_err("failed to create %s file\n", file_names[i]);
> +                       return -ENOMEM;
> +               }
> +       }
> +       dbgfs_fill_ctx_dir(dbgfs_root, dbgfs_ctxs[0]);
> +
> +       dbgfs_dirs = kmalloc_array(1, sizeof(dbgfs_root), GFP_KERNEL);
> +       dbgfs_dirs[0] = dbgfs_root;
> +
> +       return 0;
> +}
> +
> +/*
> + * Functions for the initialization
> + */
> +
> +static int __init damon_dbgfs_init(void)
> +{
> +       int rc;
> +
> +       dbgfs_ctxs = kmalloc(sizeof(*dbgfs_ctxs), GFP_KERNEL);
> +       dbgfs_ctxs[0] = dbgfs_new_ctx();
> +       if (!dbgfs_ctxs[0])
> +               return -ENOMEM;
> +       dbgfs_nr_ctxs = 1;
> +
> +       rc = __damon_dbgfs_init();
> +       if (rc)
> +               pr_err("%s: dbgfs init failed\n", __func__);
> +
> +       return rc;
> +}
> +
> +module_init(damon_dbgfs_init);
> --
> 2.17.1
>