Detailed Usages

DAMON provides below three interfaces for different users.

  • DAMON user space tool. This is for privileged people such as system administrators who want a just-working human-friendly interface. Using this, users can use the DAMON’s major features in a human-friendly way. It may not be highly tuned for special cases, though. It supports only virtual address spaces monitoring.
  • debugfs interface. This 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 is also a reference implementation of such programs. It supports only virtual address spaces monitoring.
  • Kernel Space Programming Interface. This is for kernel space programmers. Using this, users can utilize every feature of DAMON most flexibly and efficiently by writing kernel space DAMON application programs for you. You can even extend DAMON for various address spaces.

Nevertheless, you could write your own user space tool using the debugfs interface. A reference implementation is available at https://github.com/awslabs/damo. If you are a kernel programmer, you could refer to API Reference for the kernel space programming interface. For the reason, this document describes only the debugfs interface

debugfs Interface

DAMON exports three files, attrs, target_ids, and monitor_on under its debugfs directory, <debugfs>/damon/.

Attributes

Users can get and set 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. To know about the monitoring attributes in detail, please refer to the Design. For example, below commands set those values to 5 ms, 100 ms, 1,000 ms, 10 and 1000, and then 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 target process is 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.

Tracepoint for Monitoring Results

DAMON provides the monitoring results via a tracepoint, damon:damon_aggregated. While the monitoring is turned on, you could record the tracepoint events and show results using tracepoint supporting tools like perf. For example:

# echo on > monitor_on
# perf record -e damon:damon_aggregated &
# sleep 5
# kill 9 $(pidof perf)
# echo off > monitor_on
# perf script