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.

This document does not describe the kernel space programming interface in detail. For that, please refer to API Reference.

DAMON User Sapce Tool

A reference implementation of the DAMON user space tools which provides a convenient user interface is in the kernel source tree. It is located at tools/damon/damo of the tree.

The tool provides a subcommands based interface. Every subcommand provides -h option, which provides the minimal usage of it. Currently, the tool supports two subcommands, record and report.

Below example commands assume you set $PATH to point tools/damon/ for brevity. It is not mandatory for use of damo, though.

Recording Data Access Pattern

The record subcommand records the data access pattern of target workloads in a file (./ by default). You can specify the target with 1) the command for execution of the monitoring target process, 2) pid of running target process, or 3) the special keyword, ‘paddr’, if you want to monitor the system’s physical memory address space. Below example shows a command target usage:

# cd <kernel>/tools/damon/
# damo record "sleep 5"

The tool will execute sleep 5 by itself and record the data access patterns of the process. Below example shows a pid target usage:

# sleep 5 &
# damo record `pidof sleep`

Finally, below example shows the use of the special keyword, ‘paddr’:

# damo record paddr

In this case, the monitoring target regions defaults to the largetst ‘System RAM’ region specified in ‘/proc/iomem’ file. Note that the initial monitoring target region is maintained rather than dynamically updated like the virtual memory address spaces monitoring case.

The location of the recorded file can be explicitly set using -o option. You can further tune this by setting the monitoring attributes. To know about the monitoring attributes in detail, please refer to Mechanisms.

Analyzing Data Access Pattern

The report subcommand reads a data access pattern record file (if not explicitly specified using -i option, reads ./ file by default) and generates human-readable reports. You can specify what type of report you want using a sub-subcommand to report subcommand. raw, heats, and wss report types are supported for now.


raw sub-subcommand simply transforms the binary record into a human-readable text. For example:

$ damo report raw
start_time:  193485829398
rel time:                0
nr_tasks:  1
pid:  1348
nr_regions:  4
560189609000-56018abce000(  22827008):  0
7fbdff59a000-7fbdffaf1a00(   5601792):  0
7fbdffaf1a00-7fbdffbb5000(    800256):  1
7ffea0dc0000-7ffea0dfd000(    249856):  0

rel time:        100000731
nr_tasks:  1
pid:  1348
nr_regions:  6
560189609000-56018abce000(  22827008):  0
7fbdff59a000-7fbdff8ce933(   3361075):  0
7fbdff8ce933-7fbdffaf1a00(   2240717):  1
7fbdffaf1a00-7fbdffb66d99(    480153):  0
7fbdffb66d99-7fbdffbb5000(    320103):  1
7ffea0dc0000-7ffea0dfd000(    249856):  0

The first line shows the recording started timestamp (nanosecond). Records of data access patterns follows. Each record is separated by a blank line. Each record first specifies the recorded time (rel time) in relative to the start time, the number of monitored tasks in this record (nr_tasks). Recorded data access patterns of each task follow. Each data access pattern for each task shows the target’s pid (pid) and a number of monitored address regions in this access pattern (nr_regions) first. After that, each line shows the start/end address, size, and the number of observed accesses of each region.


The raw output is very detailed but hard to manually read. heats sub-subcommand plots the data in 3-dimensional form, which represents the time in x-axis, address of regions in y-axis, and the access frequency in z-axis. Users can set the resolution of the map (--tres and --ares) and start/end point of each axis (--tmin, --tmax, --amin, and --amax) via optional arguments. For example:

$ damo report heats --tres 3 --ares 3
0               0               0.0
0               7609002         0.0
0               15218004        0.0
66112620851     0               0.0
66112620851     7609002         0.0
66112620851     15218004        0.0
132225241702    0               0.0
132225241702    7609002         0.0
132225241702    15218004        0.0

This command shows a recorded access pattern in heatmap of 3x3 resolution. Therefore it shows 9 data points in total. Each line shows each of the data points. The three numbers in each line represent time in nanosecond, address, and the observed access frequency.

Users will be able to convert this text output into a heatmap image (represents z-axis values with colors) or other 3D representations using various tools such as ‘gnuplot’. For more convenience, heats sub-subcommand provides the ‘gnuplot’ based heatmap image creation. For this, you can use --heatmap option. Also, note that because it uses ‘gnuplot’ internally, it will fail if ‘gnuplot’ is not installed on your system. For example:

$ ./damo report heats --heatmap heatmap.png

Creates the heatmap image in heatmap.png file. It supports pdf, png, jpeg, and svg.

If the target address space is virtual memory address space and you plot the entire address space, the huge unmapped regions will make the picture looks only black. Therefore you should do proper zoom in / zoom out using the resolution and axis boundary-setting arguments. To make this effort minimal, you can use --guide option as below:

$ ./damo report heats --guide
time: 193485829398-198337863555 (4852034157)
region   0: 00000094564599762944-00000094564622589952 (22827008)
region   1: 00000140454009610240-00000140454016012288 (6402048)
region   2: 00000140731597193216-00000140731597443072 (249856)

The output shows unions of monitored regions (start and end addresses in byte) and the union of monitored time duration (start and end time in nanoseconds) of each target task. Therefore, it would be wise to plot the data points in each union. If no axis boundary option is given, it will automatically find the biggest union in --guide output and set the boundary in it.


The wss type extracts the distribution and chronological working set size changes from the records. For example:

$ ./damo report wss
# <percentile> <wss>
# pid   1348
# avr:  66228
0       0
25      0
50      0
75      0
100     1920615

Without any option, it shows the distribution of the working set sizes as above. It shows 0th, 25th, 50th, 75th, and 100th percentile and the average of the measured working set sizes in the access pattern records. In this case, the working set size was zero for 75th percentile but 1,920,615 bytes in max and 66,228 bytes on average.

By setting the sort key of the percentile using ‘–sortby’, you can show how the working set size has chronologically changed. For example:

$ ./damo report wss --sortby time
# <percentile> <wss>
# pid   1348
# avr:  66228
0       0
25      0
50      0
75      0
100     0

The average is still 66,228. And, because the access was spiked in very short duration and this command plots only 4 data points, we cannot show when the access spikes made. Users can specify the resolution of the distribution (--range). By giving more fine resolution, the short duration spikes could be found.

Similar to that of heats --heatmap, it also supports ‘gnuplot’ based simple visualization of the distribution via --plot option.

DAMON-based Operation Schemes

The schemes subcommand allows users to do DAMON-based memory management optimizations in a few seconds. Similar to record, it receives monitoring attributes and target. However, in addition to those, schemes receives data access pattern-based memory operation schemes, which describes what memory operation action should be applied to memory regions showing specific data access pattern. Then, it starts the data access monitoring and automatically applies the schemes to the targets.

The operation schemes should be saved in a text file in below format and passed to schemes subcommand via --schemes option.

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

The format also supports comments, several units for size and age of regions, and human readable action names. Currently supported operation actions are willneed, cold, pageout, hugepage and nohugepage. Each of the actions works same to the madvise() system call hints having the name. Please also note that the range is inclusive (closed interval), and 0 for max values means infinite. Below example schemes are possible.

# format is:
# <min/max size> <min/max frequency (0-100)> <min/max age> <action>
# B/K/M/G/T for Bytes/KiB/MiB/GiB/TiB
# us/ms/s/m/h/d for micro-seconds/milli-seconds/seconds/minutes/hours/days
# 'min/max' for possible min/max value.

# if a region keeps a high access frequency for >=100ms, put the region on
# the head of the LRU list (call madvise() with MADV_WILLNEED).
min    max      80      max     100ms   max willneed

# if a region keeps a low access frequency for >=200ms and <=one hour, put
# the region on the tail of the LRU list (call madvise() with MADV_COLD).
min     max     10      20      200ms   1h  cold

# if a region keeps a very low access frequency for >=60 seconds, swap out
# the region immediately (call madvise() with MADV_PAGEOUT).
min     max     0       10      60s     max pageout

# if a region of a size >=2MiB keeps a very high access frequency for
# >=100ms, let the region to use huge pages (call madvise() with
2M      max     90      100     100ms   max hugepage

# If a regions of a size >=2MiB keeps small access frequency for >=100ms,
# avoid the region using huge pages (call madvise() with MADV_NOHUGEPAGE).
2M      max     0       25      100ms   max nohugepage

For example, you can make a running process named ‘foo’ to use huge pages for memory regions keeping 2MB or larger size and having very high access frequency for at least 100 milliseconds using below commands:

$ echo "2M max    90 max    100ms max    hugepage" > my_thp_scheme
$ ./damo schemes --schemes my_thp_scheme `pidof foo`

debugfs Interface

DAMON exports five files, attrs, pids, record, 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 Mechanisms. 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 PIDs

To monitor the virtual memory address spaces of specific processes, users can get and set the pids of 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

Users can also monitor the physical memory address space of the system by writing a special keyword, “paddr\n” to the file. In this case, reading the file will show -1, as below:

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

Note that setting the pids doesn’t start the monitoring.

Initial Monitoring Target Regions

In case of the debugfs based monitoring, DAMON automatically sets and updates the monitoring target regions so that entire memory mappings of target processes can be covered. However, users might want to limit the monitoring region to specific address ranges, such as the heap, the stack, or specific file-mapped area. Or, some users might 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.:

<pid> <start address> <end address>

The pid should already in pids 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.


This debugfs file allows you to record monitored access patterns in a regular binary file. The recorded results are first written in an in-memory buffer and flushed to a file in batch. Users can get and 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 /

# cd <debugfs>/damon
# echo "4096 /" > record
# cat record
4096 /

The recording can be disabled by setting the buffer size zero.


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. Recording and schemes will also start work if requested before. 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.