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Docs/admin-guide/mm/damon/usage: document DAMON sysfs interface

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This commit adds detailed usage of DAMON sysfs interface in the
admin-guide document for DAMON.

Link: https://lkml.kernel.org/r/20220228081314.5770-13-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Xin Hao <xhao@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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SeongJae Park 2022-03-22 14:49:55 -07:00 committed by Linus Torvalds
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Documentation/admin-guide/mm/damon/usage.rst
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@ -4,7 +4,7 @@
Detailed Usages
===============
DAMON provides below three interfaces for different users.
DAMON provides below interfaces for different users.
- *DAMON user space tool.*
`This <https://github.com/awslabs/damo>`_ is for privileged people such as
@ -14,17 +14,21 @@ DAMON provides below three interfaces for different users.
virtual and physical address spaces monitoring. For more detail, please
refer to its `usage document
<https://github.com/awslabs/damo/blob/next/USAGE.md>`_.
- *debugfs interface.*
:ref:`This <debugfs_interface>` is for privileged user space programmers who
- *sysfs interface.*
:ref:`This <sysfs_interface>` is for privileged user space programmers who
want more optimized use of DAMON. Using this, users can use DAMON’s major
features by reading from and writing to special debugfs files. Therefore,
you can write and use your personalized DAMON debugfs wrapper programs that
reads/writes the debugfs files instead of you. The `DAMON user space tool
features by reading from and writing to special sysfs files. Therefore,
you can write and use your personalized DAMON sysfs wrapper programs that
reads/writes the sysfs files instead of you. The `DAMON user space tool
<https://github.com/awslabs/damo>`_ is one example of such programs. It
supports both virtual and physical address spaces monitoring. Note that this
interface provides only simple :ref:`statistics <damos_stats>` for the
monitoring results. For detailed monitoring results, DAMON provides a
:ref:`tracepoint <tracepoint>`.
- *debugfs interface.*
:ref:`This <debugfs_interface>` is almost identical to :ref:`sysfs interface
<sysfs_interface>`. This will be removed after next LTS kernel is released,
so users should move to the :ref:`sysfs interface <sysfs_interface>`.
- *Kernel Space Programming Interface.*
:doc:`This </vm/damon/api>` is for kernel space programmers. Using this,
users can utilize every feature of DAMON most flexibly and efficiently by
@ -32,6 +36,340 @@ DAMON provides below three interfaces for different users.
DAMON for various address spaces. For detail, please refer to the interface
:doc:`document </vm/damon/api>`.
.. _sysfs_interface:
sysfs Interface
===============
DAMON sysfs interface is built when ``CONFIG_DAMON_SYSFS`` is defined. It
creates multiple directories and files under its sysfs directory,
``<sysfs>/kernel/mm/damon/``. You can control DAMON by writing to and reading
from the files under the directory.
For a short example, users can monitor the virtual address space of a given
workload as below. ::
# cd /sys/kernel/mm/damon/admin/
# echo 1 > kdamonds/nr && echo 1 > kdamonds/0/contexts/nr
# echo vaddr > kdamonds/0/contexts/0/operations
# echo 1 > kdamonds/0/contexts/0/targets/nr
# echo $(pidof <workload>) > kdamonds/0/contexts/0/targets/0/pid
# echo on > kdamonds/0/state
Files Hierarchy
---------------
The files hierarchy of DAMON sysfs interface is shown below. In the below
figure, parents-children relations are represented with indentations, each
directory is having ``/`` suffix, and files in each directory are separated by
comma (","). ::
/sys/kernel/mm/damon/admin
│ kdamonds/nr_kdamonds
│ │ 0/state,pid
│ │ │ contexts/nr_contexts
│ │ │ │ 0/operations
│ │ │ │ │ monitoring_attrs/
│ │ │ │ │ │ intervals/sample_us,aggr_us,update_us
│ │ │ │ │ │ nr_regions/min,max
│ │ │ │ │ targets/nr_targets
│ │ │ │ │ │ 0/pid_target
│ │ │ │ │ │ │ regions/nr_regions
│ │ │ │ │ │ │ │ 0/start,end
│ │ │ │ │ │ │ │ ...
│ │ │ │ │ │ ...
│ │ │ │ │ schemes/nr_schemes
│ │ │ │ │ │ 0/action
│ │ │ │ │ │ │ access_pattern/
│ │ │ │ │ │ │ │ sz/min,max
│ │ │ │ │ │ │ │ nr_accesses/min,max
│ │ │ │ │ │ │ │ age/min,max
│ │ │ │ │ │ │ quotas/ms,bytes,reset_interval_ms
│ │ │ │ │ │ │ │ weights/sz_permil,nr_accesses_permil,age_permil
│ │ │ │ │ │ │ watermarks/metric,interval_us,high,mid,low
│ │ │ │ │ │ │ stats/nr_tried,sz_tried,nr_applied,sz_applied,qt_exceeds
│ │ │ │ │ │ ...
│ │ │ │ ...
│ │ ...
Root
----
The root of the DAMON sysfs interface is ``<sysfs>/kernel/mm/damon/``, and it
has one directory named ``admin``. The directory contains the files for
privileged user space programs' control of DAMON. User space tools or deamons
having the root permission could use this directory.
kdamonds/
---------
The monitoring-related information including request specifications and results
are called DAMON context. DAMON executes each context with a kernel thread
called kdamond, and multiple kdamonds could run in parallel.
Under the ``admin`` directory, one directory, ``kdamonds``, which has files for
controlling the kdamonds exist. In the beginning, this directory has only one
file, ``nr_kdamonds``. Writing a number (``N``) to the file creates the number
of child directories named ``0`` to ``N-1``. Each directory represents each
kdamond.
kdamonds/<N>/
-------------
In each kdamond directory, two files (``state`` and ``pid``) and one directory
(``contexts``) exist.
Reading ``state`` returns ``on`` if the kdamond is currently running, or
``off`` if it is not running. Writing ``on`` or ``off`` makes the kdamond be
in the state. Writing ``update_schemes_stats`` to ``state`` file updates the
contents of stats files for each DAMON-based operation scheme of the kdamond.
For details of the stats, please refer to :ref:`stats section
<sysfs_schemes_stats>`.
If the state is ``on``, reading ``pid`` shows the pid of the kdamond thread.
``contexts`` directory contains files for controlling the monitoring contexts
that this kdamond will execute.
kdamonds/<N>/contexts/
----------------------
In the beginning, this directory has only one file, ``nr_contexts``. Writing a
number (``N``) to the file creates the number of child directories named as
``0`` to ``N-1``. Each directory represents each monitoring context. At the
moment, only one context per kdamond is supported, so only ``0`` or ``1`` can
be written to the file.
contexts/<N>/
-------------
In each context directory, one file (``operations``) and three directories
(``monitoring_attrs``, ``targets``, and ``schemes``) exist.
DAMON supports multiple types of monitoring operations, including those for
virtual address space and the physical address space. You can set and get what
type of monitoring operations DAMON will use for the context by writing one of
below keywords to, and reading from the file.
- vaddr: Monitor virtual address spaces of specific processes
- paddr: Monitor the physical address space of the system
contexts/<N>/monitoring_attrs/
------------------------------
Files for specifying attributes of the monitoring including required quality
and efficiency of the monitoring are in ``monitoring_attrs`` directory.
Specifically, two directories, ``intervals`` and ``nr_regions`` exist in this
directory.
Under ``intervals`` directory, three files for DAMON's sampling interval
(``sample_us``), aggregation interval (``aggr_us``), and update interval
(``update_us``) exist. You can set and get the values in micro-seconds by
writing to and reading from the files.
Under ``nr_regions`` directory, two files for the lower-bound and upper-bound
of DAMON's monitoring regions (``min`` and ``max``, respectively), which
controls the monitoring overhead, exist. You can set and get the values by
writing to and rading from the files.
For more details about the intervals and monitoring regions range, please refer
to the Design document (:doc:`/vm/damon/design`).
contexts/<N>/targets/
---------------------
In the beginning, this directory has only one file, ``nr_targets``. Writing a
number (``N``) to the file creates the number of child directories named ``0``
to ``N-1``. Each directory represents each monitoring target.
targets/<N>/
------------
In each target directory, one file (``pid_target``) and one directory
(``regions``) exist.
If you wrote ``vaddr`` to the ``contexts/<N>/operations``, each target should
be a process. You can specify the process to DAMON by writing the pid of the
process to the ``pid_target`` file.
targets/<N>/regions
-------------------
When ``vaddr`` monitoring operations set is being used (``vaddr`` is written to
the ``contexts/<N>/operations`` file), DAMON automatically sets and updates the
monitoring target regions so that entire memory mappings of target processes
can be covered. However, users could want to set the initial monitoring region
to specific address ranges.
In contrast, DAMON do not automatically sets and updates the monitoring target
regions when ``paddr`` monitoring operations set is being used (``paddr`` is
written to the ``contexts/<N>/operations``). Therefore, users should set the
monitoring target regions by themselves in the case.
For such cases, users can explicitly set the initial monitoring target regions
as they want, by writing proper values to the files under this directory.
In the beginning, this directory has only one file, ``nr_regions``. Writing a
number (``N``) to the file creates the number of child directories named ``0``
to ``N-1``. Each directory represents each initial monitoring target region.
regions/<N>/
------------
In each region directory, you will find two files (``start`` and ``end``). You
can set and get the start and end addresses of the initial monitoring target
region by writing to and reading from the files, respectively.
contexts/<N>/schemes/
---------------------
For usual DAMON-based data access aware memory management optimizations, users
would normally want the system to apply a memory management action to a memory
region of a specific access pattern. DAMON receives such formalized operation
schemes from the user and applies those to the target memory regions. Users
can get and set the schemes by reading from and writing to files under this
directory.
In the beginning, this directory has only one file, ``nr_schemes``. Writing a
number (``N``) to the file creates the number of child directories named ``0``
to ``N-1``. Each directory represents each DAMON-based operation scheme.
schemes/<N>/
------------
In each scheme directory, four directories (``access_pattern``, ``quotas``,
``watermarks``, and ``stats``) and one file (``action``) exist.
The ``action`` file is for setting and getting what action you want to apply to
memory regions having specific access pattern of the interest. The keywords
that can be written to and read from the file and their meaning are as below.
- ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED``
- ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``
- ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT``
- ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``
- ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``
- ``stat``: Do nothing but count the statistics
schemes/<N>/access_pattern/
---------------------------
The target access pattern of each DAMON-based operation scheme is constructed
with three ranges including the size of the region in bytes, number of
monitored accesses per aggregate interval, and number of aggregated intervals
for the age of the region.
Under the ``access_pattern`` directory, three directories (``sz``,
``nr_accesses``, and ``age``) each having two files (``min`` and ``max``)
exist. You can set and get the access pattern for the given scheme by writing
to and reading from the ``min`` and ``max`` files under ``sz``,
``nr_accesses``, and ``age`` directories, respectively.
schemes/<N>/quotas/
-------------------
Optimal ``target access pattern`` for each ``action`` is workload dependent, so
not easy to find. Worse yet, setting a scheme of some action too aggressive
can cause severe overhead. To avoid such overhead, users can limit time and
size quota for each scheme. In detail, users can ask DAMON to try to use only
up to specific time (``time quota``) for applying the action, and to apply the
action to only up to specific amount (``size quota``) of memory regions having
the target access pattern within a given time interval (``reset interval``).
When the quota limit is expected to be exceeded, DAMON prioritizes found memory
regions of the ``target access pattern`` based on their size, access frequency,
and age. For personalized prioritization, users can set the weights for the
three properties.
Under ``quotas`` directory, three files (``ms``, ``bytes``,
``reset_interval_ms``) and one directory (``weights``) having three files
(``sz_permil``, ``nr_accesses_permil``, and ``age_permil``) in it exist.
You can set the ``time quota`` in milliseconds, ``size quota`` in bytes, and
``reset interval`` in milliseconds by writing the values to the three files,
respectively. You can also set the prioritization weights for size, access
frequency, and age in per-thousand unit by writing the values to the three
files under the ``weights`` directory.
schemes/<N>/watermarks/
-----------------------
To allow easy activation and deactivation of each scheme based on system
status, DAMON provides a feature called watermarks. The feature receives five
values called ``metric``, ``interval``, ``high``, ``mid``, and ``low``. The
``metric`` is the system metric such as free memory ratio that can be measured.
If the metric value of the system is higher than the value in ``high`` or lower
than ``low`` at the memoent, the scheme is deactivated. If the value is lower
than ``mid``, the scheme is activated.
Under the watermarks directory, five files (``metric``, ``interval_us``,
``high``, ``mid``, and ``low``) for setting each value exist. You can set and
get the five values by writing to the files, respectively.
Keywords and meanings of those that can be written to the ``metric`` file are
as below.
- none: Ignore the watermarks
- free_mem_rate: System's free memory rate (per thousand)
The ``interval`` should written in microseconds unit.
.. _sysfs_schemes_stats:
schemes/<N>/stats/
------------------
DAMON counts the total number and bytes of regions that each scheme is tried to
be applied, the two numbers for the regions that each scheme is successfully
applied, and the total number of the quota limit exceeds. This statistics can
be used for online analysis or tuning of the schemes.
The statistics can be retrieved by reading the files under ``stats`` directory
(``nr_tried``, ``sz_tried``, ``nr_applied``, ``sz_applied``, and
``qt_exceeds``), respectively. The files are not updated in real time, so you
should ask DAMON sysfs interface to updte the content of the files for the
stats by writing a special keyword, ``update_schemes_stats`` to the relevant
``kdamonds/<N>/state`` file.
Example
~~~~~~~
Below commands applies a scheme saying "If a memory region of size in [4KiB,
8KiB] is showing accesses per aggregate interval in [0, 5] for aggregate
interval in [10, 20], page out the region. For the paging out, use only up to
10ms per second, and also don't page out more than 1GiB per second. Under the
limitation, page out memory regions having longer age first. Also, check the
free memory rate of the system every 5 seconds, start the monitoring and paging
out when the free memory rate becomes lower than 50%, but stop it if the free
memory rate becomes larger than 60%, or lower than 30%". ::
# cd <sysfs>/kernel/mm/damon/admin
# # populate directories
# echo 1 > kdamonds/nr_kdamonds; echo 1 > kdamonds/0/contexts/nr_contexts;
# echo 1 > kdamonds/0/contexts/0/schemes/nr_schemes
# cd kdamonds/0/contexts/0/schemes/0
# # set the basic access pattern and the action
# echo 4096 > access_patterns/sz/min
# echo 8192 > access_patterns/sz/max
# echo 0 > access_patterns/nr_accesses/min
# echo 5 > access_patterns/nr_accesses/max
# echo 10 > access_patterns/age/min
# echo 20 > access_patterns/age/max
# echo pageout > action
# # set quotas
# echo 10 > quotas/ms
# echo $((1024*1024*1024)) > quotas/bytes
# echo 1000 > quotas/reset_interval_ms
# # set watermark
# echo free_mem_rate > watermarks/metric
# echo 5000000 > watermarks/interval_us
# echo 600 > watermarks/high
# echo 500 > watermarks/mid
# echo 300 > watermarks/low
Please note that it's highly recommended to use user space tools like `damo
<https://github.com/awslabs/damo>`_ rather than manually reading and writing
the files as above. Above is only for an example.
.. _debugfs_interface: