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From:   Leonard Foerster <foersleo@amazon.com>
To:     SeongJae Park <sjpark@amazon.com>
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Subject: Re: [PATCH v13 09/15] mm/damon: Add debugfs interface
Date:   Wed, 27 May 2020 13:24:29 +0200
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On 2020-05-25T11:15:06+02:00 SeongJae Park <sjpark@amazon.com> wrote:

> From: SeongJae Park <sjpark@amazon.de>
> 
> 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 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>