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 both virtual and physical 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 both virtual and physical 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 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 five files, attrs, target_ids, init_regions, schemes and monitor_on under its debugfs directory, <debugfs>/damon/.


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

Users can also monitor the physical memory address space of the system by writing a special keyword, “paddr\n” to the file. Because physical address space monitoring doesn’t support multiple targets, reading the file will show a fake value, 42, as below:

# cd <debugfs>/damon
# echo paddr > target_ids
# cat target_ids

Note that setting the target ids doesn’t start the monitoring.

Initial Monitoring Target Regions

In case of the virtual address space monitoring, DAMON automatically sets and updates the monitoring target regions so that entire memory mappings of target processes can be covered. However, users can want to limit the monitoring region to specific address ranges, such as the heap, the stack, or specific file-mapped area. Or, some users can know the initial access pattern of their workloads and therefore want to set optimal initial regions for the ‘adaptive regions adjustment’.

In contrast, DAMON do not automatically sets and updates the monitoring target regions in case of physical memory monitoring. Therefore, users should set the monitoring target regions by themselves.

In such cases, users can explicitly set the initial monitoring target regions as they want, by writing proper values to the init_regions file. Each line of the input should represent one region in below form.:

<target id> <start address> <end address>

The target id should already in target_ids file, and the regions should be passed in address order. For example, below commands will set a couple of address ranges, 1-100 and 100-200 as the initial monitoring target region of process 42, and another couple of address ranges, 20-40 and 50-100 as that of process 4242.:

# cd <debugfs>/damon
# echo "42   1       100
        42   100     200
        4242 20      40
        4242 50      100" > init_regions

Note that this sets the initial monitoring target regions only. In case of virtual memory monitoring, DAMON will automatically updates the boundary of the regions after one regions update interval. Therefore, users should set the regions update interval large enough in this case, if they don’t want the update.


For usual DAMON-based data access aware memory management optimizations, users would simply want the system to apply a memory management action to a memory region of a specific size having a specific access frequency for a specific time. DAMON receives such formalized operation schemes from the user and applies those to the target processes. It also counts the total number and size of regions that each scheme is applied. This statistics can be used for online analysis or tuning of the schemes.

Users can get and set the schemes by reading from and writing to schemes debugfs file. Reading the file also shows the statistics of each scheme. To the file, each of the schemes should be represented in each line in below form:

min-size max-size min-acc max-acc min-age max-age action

Note that the ranges are closed interval. Bytes for the size of regions (min-size and max-size), number of monitored accesses per aggregate interval for access frequency (min-acc and max-acc), number of aggregate intervals for the age of regions (min-age and max-age), and a predefined integer for memory management actions should be used. The supported numbers and their meanings are as below.

  • 0: Call madvise() for the region with MADV_WILLNEED

  • 1: Call madvise() for the region with MADV_COLD

  • 2: Call madvise() for the region with MADV_PAGEOUT

  • 3: Call madvise() for the region with MADV_HUGEPAGE

  • 4: Call madvise() for the region with MADV_NOHUGEPAGE

  • 5: Do nothing but count the statistics

You can disable schemes by simply writing an empty string to the file. For 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”, check the entered scheme again, and finally remove the scheme.

# cd <debugfs>/damon
# echo "4096 8192    0 5    10 20    2" > schemes
# cat schemes
4096 8192 0 5 10 20 2 0 0
# echo > schemes

The last two integers in the 4th line of above example is the total number and the total size of the regions that the scheme is applied.

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

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