usage.rst (29089B)
1.. SPDX-License-Identifier: GPL-2.0 2 3=============== 4Detailed Usages 5=============== 6 7DAMON provides below interfaces for different users. 8 9- *DAMON user space tool.* 10 `This <https://github.com/awslabs/damo>`_ is for privileged people such as 11 system administrators who want a just-working human-friendly interface. 12 Using this, users can use the DAMON’s major features in a human-friendly way. 13 It may not be highly tuned for special cases, though. It supports both 14 virtual and physical address spaces monitoring. For more detail, please 15 refer to its `usage document 16 <https://github.com/awslabs/damo/blob/next/USAGE.md>`_. 17- *sysfs interface.* 18 :ref:`This <sysfs_interface>` is for privileged user space programmers who 19 want more optimized use of DAMON. Using this, users can use DAMON’s major 20 features by reading from and writing to special sysfs files. Therefore, 21 you can write and use your personalized DAMON sysfs wrapper programs that 22 reads/writes the sysfs files instead of you. The `DAMON user space tool 23 <https://github.com/awslabs/damo>`_ is one example of such programs. It 24 supports both virtual and physical address spaces monitoring. Note that this 25 interface provides only simple :ref:`statistics <damos_stats>` for the 26 monitoring results. For detailed monitoring results, DAMON provides a 27 :ref:`tracepoint <tracepoint>`. 28- *debugfs interface.* 29 :ref:`This <debugfs_interface>` is almost identical to :ref:`sysfs interface 30 <sysfs_interface>`. This will be removed after next LTS kernel is released, 31 so users should move to the :ref:`sysfs interface <sysfs_interface>`. 32- *Kernel Space Programming Interface.* 33 :doc:`This </vm/damon/api>` is for kernel space programmers. Using this, 34 users can utilize every feature of DAMON most flexibly and efficiently by 35 writing kernel space DAMON application programs for you. You can even extend 36 DAMON for various address spaces. For detail, please refer to the interface 37 :doc:`document </vm/damon/api>`. 38 39.. _sysfs_interface: 40 41sysfs Interface 42=============== 43 44DAMON sysfs interface is built when ``CONFIG_DAMON_SYSFS`` is defined. It 45creates multiple directories and files under its sysfs directory, 46``<sysfs>/kernel/mm/damon/``. You can control DAMON by writing to and reading 47from the files under the directory. 48 49For a short example, users can monitor the virtual address space of a given 50workload as below. :: 51 52 # cd /sys/kernel/mm/damon/admin/ 53 # echo 1 > kdamonds/nr && echo 1 > kdamonds/0/contexts/nr 54 # echo vaddr > kdamonds/0/contexts/0/operations 55 # echo 1 > kdamonds/0/contexts/0/targets/nr 56 # echo $(pidof <workload>) > kdamonds/0/contexts/0/targets/0/pid 57 # echo on > kdamonds/0/state 58 59Files Hierarchy 60--------------- 61 62The files hierarchy of DAMON sysfs interface is shown below. In the below 63figure, parents-children relations are represented with indentations, each 64directory is having ``/`` suffix, and files in each directory are separated by 65comma (","). :: 66 67 /sys/kernel/mm/damon/admin 68 │ kdamonds/nr_kdamonds 69 │ │ 0/state,pid 70 │ │ │ contexts/nr_contexts 71 │ │ │ │ 0/avail_operations,operations 72 │ │ │ │ │ monitoring_attrs/ 73 │ │ │ │ │ │ intervals/sample_us,aggr_us,update_us 74 │ │ │ │ │ │ nr_regions/min,max 75 │ │ │ │ │ targets/nr_targets 76 │ │ │ │ │ │ 0/pid_target 77 │ │ │ │ │ │ │ regions/nr_regions 78 │ │ │ │ │ │ │ │ 0/start,end 79 │ │ │ │ │ │ │ │ ... 80 │ │ │ │ │ │ ... 81 │ │ │ │ │ schemes/nr_schemes 82 │ │ │ │ │ │ 0/action 83 │ │ │ │ │ │ │ access_pattern/ 84 │ │ │ │ │ │ │ │ sz/min,max 85 │ │ │ │ │ │ │ │ nr_accesses/min,max 86 │ │ │ │ │ │ │ │ age/min,max 87 │ │ │ │ │ │ │ quotas/ms,bytes,reset_interval_ms 88 │ │ │ │ │ │ │ │ weights/sz_permil,nr_accesses_permil,age_permil 89 │ │ │ │ │ │ │ watermarks/metric,interval_us,high,mid,low 90 │ │ │ │ │ │ │ stats/nr_tried,sz_tried,nr_applied,sz_applied,qt_exceeds 91 │ │ │ │ │ │ ... 92 │ │ │ │ ... 93 │ │ ... 94 95Root 96---- 97 98The root of the DAMON sysfs interface is ``<sysfs>/kernel/mm/damon/``, and it 99has one directory named ``admin``. The directory contains the files for 100privileged user space programs' control of DAMON. User space tools or deamons 101having the root permission could use this directory. 102 103kdamonds/ 104--------- 105 106The monitoring-related information including request specifications and results 107are called DAMON context. DAMON executes each context with a kernel thread 108called kdamond, and multiple kdamonds could run in parallel. 109 110Under the ``admin`` directory, one directory, ``kdamonds``, which has files for 111controlling the kdamonds exist. In the beginning, this directory has only one 112file, ``nr_kdamonds``. Writing a number (``N``) to the file creates the number 113of child directories named ``0`` to ``N-1``. Each directory represents each 114kdamond. 115 116kdamonds/<N>/ 117------------- 118 119In each kdamond directory, two files (``state`` and ``pid``) and one directory 120(``contexts``) exist. 121 122Reading ``state`` returns ``on`` if the kdamond is currently running, or 123``off`` if it is not running. Writing ``on`` or ``off`` makes the kdamond be 124in the state. Writing ``commit`` to the ``state`` file makes kdamond reads the 125user inputs in the sysfs files except ``state`` file again. Writing 126``update_schemes_stats`` to ``state`` file updates the contents of stats files 127for each DAMON-based operation scheme of the kdamond. For details of the 128stats, please refer to :ref:`stats section <sysfs_schemes_stats>`. 129 130If the state is ``on``, reading ``pid`` shows the pid of the kdamond thread. 131 132``contexts`` directory contains files for controlling the monitoring contexts 133that this kdamond will execute. 134 135kdamonds/<N>/contexts/ 136---------------------- 137 138In the beginning, this directory has only one file, ``nr_contexts``. Writing a 139number (``N``) to the file creates the number of child directories named as 140``0`` to ``N-1``. Each directory represents each monitoring context. At the 141moment, only one context per kdamond is supported, so only ``0`` or ``1`` can 142be written to the file. 143 144contexts/<N>/ 145------------- 146 147In each context directory, two files (``avail_operations`` and ``operations``) 148and three directories (``monitoring_attrs``, ``targets``, and ``schemes``) 149exist. 150 151DAMON supports multiple types of monitoring operations, including those for 152virtual address space and the physical address space. You can get the list of 153available monitoring operations set on the currently running kernel by reading 154``avail_operations`` file. Based on the kernel configuration, the file will 155list some or all of below keywords. 156 157 - vaddr: Monitor virtual address spaces of specific processes 158 - fvaddr: Monitor fixed virtual address ranges 159 - paddr: Monitor the physical address space of the system 160 161Please refer to :ref:`regions sysfs directory <sysfs_regions>` for detailed 162differences between the operations sets in terms of the monitoring target 163regions. 164 165You can set and get what type of monitoring operations DAMON will use for the 166context by writing one of the keywords listed in ``avail_operations`` file and 167reading from the ``operations`` file. 168 169contexts/<N>/monitoring_attrs/ 170------------------------------ 171 172Files for specifying attributes of the monitoring including required quality 173and efficiency of the monitoring are in ``monitoring_attrs`` directory. 174Specifically, two directories, ``intervals`` and ``nr_regions`` exist in this 175directory. 176 177Under ``intervals`` directory, three files for DAMON's sampling interval 178(``sample_us``), aggregation interval (``aggr_us``), and update interval 179(``update_us``) exist. You can set and get the values in micro-seconds by 180writing to and reading from the files. 181 182Under ``nr_regions`` directory, two files for the lower-bound and upper-bound 183of DAMON's monitoring regions (``min`` and ``max``, respectively), which 184controls the monitoring overhead, exist. You can set and get the values by 185writing to and rading from the files. 186 187For more details about the intervals and monitoring regions range, please refer 188to the Design document (:doc:`/vm/damon/design`). 189 190contexts/<N>/targets/ 191--------------------- 192 193In the beginning, this directory has only one file, ``nr_targets``. Writing a 194number (``N``) to the file creates the number of child directories named ``0`` 195to ``N-1``. Each directory represents each monitoring target. 196 197targets/<N>/ 198------------ 199 200In each target directory, one file (``pid_target``) and one directory 201(``regions``) exist. 202 203If you wrote ``vaddr`` to the ``contexts/<N>/operations``, each target should 204be a process. You can specify the process to DAMON by writing the pid of the 205process to the ``pid_target`` file. 206 207.. _sysfs_regions: 208 209targets/<N>/regions 210------------------- 211 212When ``vaddr`` monitoring operations set is being used (``vaddr`` is written to 213the ``contexts/<N>/operations`` file), DAMON automatically sets and updates the 214monitoring target regions so that entire memory mappings of target processes 215can be covered. However, users could want to set the initial monitoring region 216to specific address ranges. 217 218In contrast, DAMON do not automatically sets and updates the monitoring target 219regions when ``fvaddr`` or ``paddr`` monitoring operations sets are being used 220(``fvaddr`` or ``paddr`` have written to the ``contexts/<N>/operations``). 221Therefore, users should set the monitoring target regions by themselves in the 222cases. 223 224For such cases, users can explicitly set the initial monitoring target regions 225as they want, by writing proper values to the files under this directory. 226 227In the beginning, this directory has only one file, ``nr_regions``. Writing a 228number (``N``) to the file creates the number of child directories named ``0`` 229to ``N-1``. Each directory represents each initial monitoring target region. 230 231regions/<N>/ 232------------ 233 234In each region directory, you will find two files (``start`` and ``end``). You 235can set and get the start and end addresses of the initial monitoring target 236region by writing to and reading from the files, respectively. 237 238contexts/<N>/schemes/ 239--------------------- 240 241For usual DAMON-based data access aware memory management optimizations, users 242would normally want the system to apply a memory management action to a memory 243region of a specific access pattern. DAMON receives such formalized operation 244schemes from the user and applies those to the target memory regions. Users 245can get and set the schemes by reading from and writing to files under this 246directory. 247 248In the beginning, this directory has only one file, ``nr_schemes``. Writing a 249number (``N``) to the file creates the number of child directories named ``0`` 250to ``N-1``. Each directory represents each DAMON-based operation scheme. 251 252schemes/<N>/ 253------------ 254 255In each scheme directory, four directories (``access_pattern``, ``quotas``, 256``watermarks``, and ``stats``) and one file (``action``) exist. 257 258The ``action`` file is for setting and getting what action you want to apply to 259memory regions having specific access pattern of the interest. The keywords 260that can be written to and read from the file and their meaning are as below. 261 262 - ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED`` 263 - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD`` 264 - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT`` 265 - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE`` 266 - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE`` 267 - ``stat``: Do nothing but count the statistics 268 269schemes/<N>/access_pattern/ 270--------------------------- 271 272The target access pattern of each DAMON-based operation scheme is constructed 273with three ranges including the size of the region in bytes, number of 274monitored accesses per aggregate interval, and number of aggregated intervals 275for the age of the region. 276 277Under the ``access_pattern`` directory, three directories (``sz``, 278``nr_accesses``, and ``age``) each having two files (``min`` and ``max``) 279exist. You can set and get the access pattern for the given scheme by writing 280to and reading from the ``min`` and ``max`` files under ``sz``, 281``nr_accesses``, and ``age`` directories, respectively. 282 283schemes/<N>/quotas/ 284------------------- 285 286Optimal ``target access pattern`` for each ``action`` is workload dependent, so 287not easy to find. Worse yet, setting a scheme of some action too aggressive 288can cause severe overhead. To avoid such overhead, users can limit time and 289size quota for each scheme. In detail, users can ask DAMON to try to use only 290up to specific time (``time quota``) for applying the action, and to apply the 291action to only up to specific amount (``size quota``) of memory regions having 292the target access pattern within a given time interval (``reset interval``). 293 294When the quota limit is expected to be exceeded, DAMON prioritizes found memory 295regions of the ``target access pattern`` based on their size, access frequency, 296and age. For personalized prioritization, users can set the weights for the 297three properties. 298 299Under ``quotas`` directory, three files (``ms``, ``bytes``, 300``reset_interval_ms``) and one directory (``weights``) having three files 301(``sz_permil``, ``nr_accesses_permil``, and ``age_permil``) in it exist. 302 303You can set the ``time quota`` in milliseconds, ``size quota`` in bytes, and 304``reset interval`` in milliseconds by writing the values to the three files, 305respectively. You can also set the prioritization weights for size, access 306frequency, and age in per-thousand unit by writing the values to the three 307files under the ``weights`` directory. 308 309schemes/<N>/watermarks/ 310----------------------- 311 312To allow easy activation and deactivation of each scheme based on system 313status, DAMON provides a feature called watermarks. The feature receives five 314values called ``metric``, ``interval``, ``high``, ``mid``, and ``low``. The 315``metric`` is the system metric such as free memory ratio that can be measured. 316If the metric value of the system is higher than the value in ``high`` or lower 317than ``low`` at the memoent, the scheme is deactivated. If the value is lower 318than ``mid``, the scheme is activated. 319 320Under the watermarks directory, five files (``metric``, ``interval_us``, 321``high``, ``mid``, and ``low``) for setting each value exist. You can set and 322get the five values by writing to the files, respectively. 323 324Keywords and meanings of those that can be written to the ``metric`` file are 325as below. 326 327 - none: Ignore the watermarks 328 - free_mem_rate: System's free memory rate (per thousand) 329 330The ``interval`` should written in microseconds unit. 331 332.. _sysfs_schemes_stats: 333 334schemes/<N>/stats/ 335------------------ 336 337DAMON counts the total number and bytes of regions that each scheme is tried to 338be applied, the two numbers for the regions that each scheme is successfully 339applied, and the total number of the quota limit exceeds. This statistics can 340be used for online analysis or tuning of the schemes. 341 342The statistics can be retrieved by reading the files under ``stats`` directory 343(``nr_tried``, ``sz_tried``, ``nr_applied``, ``sz_applied``, and 344``qt_exceeds``), respectively. The files are not updated in real time, so you 345should ask DAMON sysfs interface to updte the content of the files for the 346stats by writing a special keyword, ``update_schemes_stats`` to the relevant 347``kdamonds/<N>/state`` file. 348 349Example 350~~~~~~~ 351 352Below commands applies a scheme saying "If a memory region of size in [4KiB, 3538KiB] is showing accesses per aggregate interval in [0, 5] for aggregate 354interval in [10, 20], page out the region. For the paging out, use only up to 35510ms per second, and also don't page out more than 1GiB per second. Under the 356limitation, page out memory regions having longer age first. Also, check the 357free memory rate of the system every 5 seconds, start the monitoring and paging 358out when the free memory rate becomes lower than 50%, but stop it if the free 359memory rate becomes larger than 60%, or lower than 30%". :: 360 361 # cd <sysfs>/kernel/mm/damon/admin 362 # # populate directories 363 # echo 1 > kdamonds/nr_kdamonds; echo 1 > kdamonds/0/contexts/nr_contexts; 364 # echo 1 > kdamonds/0/contexts/0/schemes/nr_schemes 365 # cd kdamonds/0/contexts/0/schemes/0 366 # # set the basic access pattern and the action 367 # echo 4096 > access_patterns/sz/min 368 # echo 8192 > access_patterns/sz/max 369 # echo 0 > access_patterns/nr_accesses/min 370 # echo 5 > access_patterns/nr_accesses/max 371 # echo 10 > access_patterns/age/min 372 # echo 20 > access_patterns/age/max 373 # echo pageout > action 374 # # set quotas 375 # echo 10 > quotas/ms 376 # echo $((1024*1024*1024)) > quotas/bytes 377 # echo 1000 > quotas/reset_interval_ms 378 # # set watermark 379 # echo free_mem_rate > watermarks/metric 380 # echo 5000000 > watermarks/interval_us 381 # echo 600 > watermarks/high 382 # echo 500 > watermarks/mid 383 # echo 300 > watermarks/low 384 385Please note that it's highly recommended to use user space tools like `damo 386<https://github.com/awslabs/damo>`_ rather than manually reading and writing 387the files as above. Above is only for an example. 388 389.. _debugfs_interface: 390 391debugfs Interface 392================= 393 394DAMON exports eight files, ``attrs``, ``target_ids``, ``init_regions``, 395``schemes``, ``monitor_on``, ``kdamond_pid``, ``mk_contexts`` and 396``rm_contexts`` under its debugfs directory, ``<debugfs>/damon/``. 397 398 399Attributes 400---------- 401 402Users can get and set the ``sampling interval``, ``aggregation interval``, 403``update interval``, and min/max number of monitoring target regions by 404reading from and writing to the ``attrs`` file. To know about the monitoring 405attributes in detail, please refer to the :doc:`/vm/damon/design`. For 406example, below commands set those values to 5 ms, 100 ms, 1,000 ms, 10 and 4071000, and then check it again:: 408 409 # cd <debugfs>/damon 410 # echo 5000 100000 1000000 10 1000 > attrs 411 # cat attrs 412 5000 100000 1000000 10 1000 413 414 415Target IDs 416---------- 417 418Some types of address spaces supports multiple monitoring target. For example, 419the virtual memory address spaces monitoring can have multiple processes as the 420monitoring targets. Users can set the targets by writing relevant id values of 421the targets to, and get the ids of the current targets by reading from the 422``target_ids`` file. In case of the virtual address spaces monitoring, the 423values should be pids of the monitoring target processes. For example, below 424commands set processes having pids 42 and 4242 as the monitoring targets and 425check it again:: 426 427 # cd <debugfs>/damon 428 # echo 42 4242 > target_ids 429 # cat target_ids 430 42 4242 431 432Users can also monitor the physical memory address space of the system by 433writing a special keyword, "``paddr\n``" to the file. Because physical address 434space monitoring doesn't support multiple targets, reading the file will show a 435fake value, ``42``, as below:: 436 437 # cd <debugfs>/damon 438 # echo paddr > target_ids 439 # cat target_ids 440 42 441 442Note that setting the target ids doesn't start the monitoring. 443 444 445Initial Monitoring Target Regions 446--------------------------------- 447 448In case of the virtual address space monitoring, DAMON automatically sets and 449updates the monitoring target regions so that entire memory mappings of target 450processes can be covered. However, users can want to limit the monitoring 451region to specific address ranges, such as the heap, the stack, or specific 452file-mapped area. Or, some users can know the initial access pattern of their 453workloads and therefore want to set optimal initial regions for the 'adaptive 454regions adjustment'. 455 456In contrast, DAMON do not automatically sets and updates the monitoring target 457regions in case of physical memory monitoring. Therefore, users should set the 458monitoring target regions by themselves. 459 460In such cases, users can explicitly set the initial monitoring target regions 461as they want, by writing proper values to the ``init_regions`` file. Each line 462of the input should represent one region in below form.:: 463 464 <target idx> <start address> <end address> 465 466The ``target idx`` should be the index of the target in ``target_ids`` file, 467starting from ``0``, and the regions should be passed in address order. For 468example, below commands will set a couple of address ranges, ``1-100`` and 469``100-200`` as the initial monitoring target region of pid 42, which is the 470first one (index ``0``) in ``target_ids``, and another couple of address 471ranges, ``20-40`` and ``50-100`` as that of pid 4242, which is the second one 472(index ``1``) in ``target_ids``.:: 473 474 # cd <debugfs>/damon 475 # cat target_ids 476 42 4242 477 # echo "0 1 100 478 0 100 200 479 1 20 40 480 1 50 100" > init_regions 481 482Note that this sets the initial monitoring target regions only. In case of 483virtual memory monitoring, DAMON will automatically updates the boundary of the 484regions after one ``update interval``. Therefore, users should set the 485``update interval`` large enough in this case, if they don't want the 486update. 487 488 489Schemes 490------- 491 492For usual DAMON-based data access aware memory management optimizations, users 493would simply want the system to apply a memory management action to a memory 494region of a specific access pattern. DAMON receives such formalized operation 495schemes from the user and applies those to the target processes. 496 497Users can get and set the schemes by reading from and writing to ``schemes`` 498debugfs file. Reading the file also shows the statistics of each scheme. To 499the file, each of the schemes should be represented in each line in below 500form:: 501 502 <target access pattern> <action> <quota> <watermarks> 503 504You can disable schemes by simply writing an empty string to the file. 505 506Target Access Pattern 507~~~~~~~~~~~~~~~~~~~~~ 508 509The ``<target access pattern>`` is constructed with three ranges in below 510form:: 511 512 min-size max-size min-acc max-acc min-age max-age 513 514Specifically, bytes for the size of regions (``min-size`` and ``max-size``), 515number of monitored accesses per aggregate interval for access frequency 516(``min-acc`` and ``max-acc``), number of aggregate intervals for the age of 517regions (``min-age`` and ``max-age``) are specified. Note that the ranges are 518closed interval. 519 520Action 521~~~~~~ 522 523The ``<action>`` is a predefined integer for memory management actions, which 524DAMON will apply to the regions having the target access pattern. The 525supported numbers and their meanings are as below. 526 527 - 0: Call ``madvise()`` for the region with ``MADV_WILLNEED`` 528 - 1: Call ``madvise()`` for the region with ``MADV_COLD`` 529 - 2: Call ``madvise()`` for the region with ``MADV_PAGEOUT`` 530 - 3: Call ``madvise()`` for the region with ``MADV_HUGEPAGE`` 531 - 4: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE`` 532 - 5: Do nothing but count the statistics 533 534Quota 535~~~~~ 536 537Optimal ``target access pattern`` for each ``action`` is workload dependent, so 538not easy to find. Worse yet, setting a scheme of some action too aggressive 539can cause severe overhead. To avoid such overhead, users can limit time and 540size quota for the scheme via the ``<quota>`` in below form:: 541 542 <ms> <sz> <reset interval> <priority weights> 543 544This makes DAMON to try to use only up to ``<ms>`` milliseconds for applying 545the action to memory regions of the ``target access pattern`` within the 546``<reset interval>`` milliseconds, and to apply the action to only up to 547``<sz>`` bytes of memory regions within the ``<reset interval>``. Setting both 548``<ms>`` and ``<sz>`` zero disables the quota limits. 549 550When the quota limit is expected to be exceeded, DAMON prioritizes found memory 551regions of the ``target access pattern`` based on their size, access frequency, 552and age. For personalized prioritization, users can set the weights for the 553three properties in ``<priority weights>`` in below form:: 554 555 <size weight> <access frequency weight> <age weight> 556 557Watermarks 558~~~~~~~~~~ 559 560Some schemes would need to run based on current value of the system's specific 561metrics like free memory ratio. For such cases, users can specify watermarks 562for the condition.:: 563 564 <metric> <check interval> <high mark> <middle mark> <low mark> 565 566``<metric>`` is a predefined integer for the metric to be checked. The 567supported numbers and their meanings are as below. 568 569 - 0: Ignore the watermarks 570 - 1: System's free memory rate (per thousand) 571 572The value of the metric is checked every ``<check interval>`` microseconds. 573 574If the value is higher than ``<high mark>`` or lower than ``<low mark>``, the 575scheme is deactivated. If the value is lower than ``<mid mark>``, the scheme 576is activated. 577 578.. _damos_stats: 579 580Statistics 581~~~~~~~~~~ 582 583It also counts the total number and bytes of regions that each scheme is tried 584to be applied, the two numbers for the regions that each scheme is successfully 585applied, and the total number of the quota limit exceeds. This statistics can 586be used for online analysis or tuning of the schemes. 587 588The statistics can be shown by reading the ``schemes`` file. Reading the file 589will show each scheme you entered in each line, and the five numbers for the 590statistics will be added at the end of each line. 591 592Example 593~~~~~~~ 594 595Below commands applies a scheme saying "If a memory region of size in [4KiB, 5968KiB] is showing accesses per aggregate interval in [0, 5] for aggregate 597interval in [10, 20], page out the region. For the paging out, use only up to 59810ms per second, and also don't page out more than 1GiB per second. Under the 599limitation, page out memory regions having longer age first. Also, check the 600free memory rate of the system every 5 seconds, start the monitoring and paging 601out when the free memory rate becomes lower than 50%, but stop it if the free 602memory rate becomes larger than 60%, or lower than 30%".:: 603 604 # cd <debugfs>/damon 605 # scheme="4096 8192 0 5 10 20 2" # target access pattern and action 606 # scheme+=" 10 $((1024*1024*1024)) 1000" # quotas 607 # scheme+=" 0 0 100" # prioritization weights 608 # scheme+=" 1 5000000 600 500 300" # watermarks 609 # echo "$scheme" > schemes 610 611 612Turning On/Off 613-------------- 614 615Setting the files as described above doesn't incur effect unless you explicitly 616start the monitoring. You can start, stop, and check the current status of the 617monitoring by writing to and reading from the ``monitor_on`` file. Writing 618``on`` to the file starts the monitoring of the targets with the attributes. 619Writing ``off`` to the file stops those. DAMON also stops if every target 620process is terminated. Below example commands turn on, off, and check the 621status of DAMON:: 622 623 # cd <debugfs>/damon 624 # echo on > monitor_on 625 # echo off > monitor_on 626 # cat monitor_on 627 off 628 629Please note that you cannot write to the above-mentioned debugfs files while 630the monitoring is turned on. If you write to the files while DAMON is running, 631an error code such as ``-EBUSY`` will be returned. 632 633 634Monitoring Thread PID 635--------------------- 636 637DAMON does requested monitoring with a kernel thread called ``kdamond``. You 638can get the pid of the thread by reading the ``kdamond_pid`` file. When the 639monitoring is turned off, reading the file returns ``none``. :: 640 641 # cd <debugfs>/damon 642 # cat monitor_on 643 off 644 # cat kdamond_pid 645 none 646 # echo on > monitor_on 647 # cat kdamond_pid 648 18594 649 650 651Using Multiple Monitoring Threads 652--------------------------------- 653 654One ``kdamond`` thread is created for each monitoring context. You can create 655and remove monitoring contexts for multiple ``kdamond`` required use case using 656the ``mk_contexts`` and ``rm_contexts`` files. 657 658Writing the name of the new context to the ``mk_contexts`` file creates a 659directory of the name on the DAMON debugfs directory. The directory will have 660DAMON debugfs files for the context. :: 661 662 # cd <debugfs>/damon 663 # ls foo 664 # ls: cannot access 'foo': No such file or directory 665 # echo foo > mk_contexts 666 # ls foo 667 # attrs init_regions kdamond_pid schemes target_ids 668 669If the context is not needed anymore, you can remove it and the corresponding 670directory by putting the name of the context to the ``rm_contexts`` file. :: 671 672 # echo foo > rm_contexts 673 # ls foo 674 # ls: cannot access 'foo': No such file or directory 675 676Note that ``mk_contexts``, ``rm_contexts``, and ``monitor_on`` files are in the 677root directory only. 678 679 680.. _tracepoint: 681 682Tracepoint for Monitoring Results 683================================= 684 685DAMON provides the monitoring results via a tracepoint, 686``damon:damon_aggregated``. While the monitoring is turned on, you could 687record the tracepoint events and show results using tracepoint supporting tools 688like ``perf``. For example:: 689 690 # echo on > monitor_on 691 # perf record -e damon:damon_aggregated & 692 # sleep 5 693 # kill 9 $(pidof perf) 694 # echo off > monitor_on 695 # perf script