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. For more detail, 14 please refer to its `usage document 15 <https://github.com/awslabs/damo/blob/next/USAGE.md>`_. 16- *sysfs interface.* 17 :ref:`This <sysfs_interface>` is for privileged user space programmers who 18 want more optimized use of DAMON. Using this, users can use DAMON’s major 19 features by reading from and writing to special sysfs files. Therefore, 20 you can write and use your personalized DAMON sysfs wrapper programs that 21 reads/writes the sysfs files instead of you. The `DAMON user space tool 22 <https://github.com/awslabs/damo>`_ is one example of such programs. Note 23 that this interface provides only simple :ref:`statistics <damos_stats>` for 24 the monitoring results. For detailed monitoring results, DAMON provides a 25 :ref:`tracepoint <tracepoint>`. 26- *debugfs interface. (DEPRECATED!)* 27 :ref:`This <debugfs_interface>` is almost identical to :ref:`sysfs interface 28 <sysfs_interface>`. This is deprecated, so users should move to the 29 :ref:`sysfs interface <sysfs_interface>`. If you depend on this and cannot 30 move, please report your usecase to damon@lists.linux.dev and 31 linux-mm@kvack.org. 32- *Kernel Space Programming Interface.* 33 :doc:`This </mm/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 </mm/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_kdamonds && echo 1 > kdamonds/0/contexts/nr_contexts 54 # echo vaddr > kdamonds/0/contexts/0/operations 55 # echo 1 > kdamonds/0/contexts/0/targets/nr_targets 56 # echo $(pidof <workload>) > kdamonds/0/contexts/0/targets/0/pid_target 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 │ │ │ │ │ │ │ filters/nr_filters 91 │ │ │ │ │ │ │ │ 0/type,matching,memcg_id 92 │ │ │ │ │ │ │ stats/nr_tried,sz_tried,nr_applied,sz_applied,qt_exceeds 93 │ │ │ │ │ │ │ tried_regions/ 94 │ │ │ │ │ │ │ │ 0/start,end,nr_accesses,age 95 │ │ │ │ │ │ │ │ ... 96 │ │ │ │ │ │ ... 97 │ │ │ │ ... 98 │ │ ... 99 100Root 101---- 102 103The root of the DAMON sysfs interface is ``<sysfs>/kernel/mm/damon/``, and it 104has one directory named ``admin``. The directory contains the files for 105privileged user space programs' control of DAMON. User space tools or deamons 106having the root permission could use this directory. 107 108kdamonds/ 109--------- 110 111The monitoring-related information including request specifications and results 112are called DAMON context. DAMON executes each context with a kernel thread 113called kdamond, and multiple kdamonds could run in parallel. 114 115Under the ``admin`` directory, one directory, ``kdamonds``, which has files for 116controlling the kdamonds exist. In the beginning, this directory has only one 117file, ``nr_kdamonds``. Writing a number (``N``) to the file creates the number 118of child directories named ``0`` to ``N-1``. Each directory represents each 119kdamond. 120 121kdamonds/<N>/ 122------------- 123 124In each kdamond directory, two files (``state`` and ``pid``) and one directory 125(``contexts``) exist. 126 127Reading ``state`` returns ``on`` if the kdamond is currently running, or 128``off`` if it is not running. Writing ``on`` or ``off`` makes the kdamond be 129in the state. Writing ``commit`` to the ``state`` file makes kdamond reads the 130user inputs in the sysfs files except ``state`` file again. Writing 131``update_schemes_stats`` to ``state`` file updates the contents of stats files 132for each DAMON-based operation scheme of the kdamond. For details of the 133stats, please refer to :ref:`stats section <sysfs_schemes_stats>`. Writing 134``update_schemes_tried_regions`` to ``state`` file updates the DAMON-based 135operation scheme action tried regions directory for each DAMON-based operation 136scheme of the kdamond. Writing ``clear_schemes_tried_regions`` to ``state`` 137file clears the DAMON-based operating scheme action tried regions directory for 138each DAMON-based operation scheme of the kdamond. For details of the 139DAMON-based operation scheme action tried regions directory, please refer to 140:ref:`tried_regions section <sysfs_schemes_tried_regions>`. 141 142If the state is ``on``, reading ``pid`` shows the pid of the kdamond thread. 143 144``contexts`` directory contains files for controlling the monitoring contexts 145that this kdamond will execute. 146 147kdamonds/<N>/contexts/ 148---------------------- 149 150In the beginning, this directory has only one file, ``nr_contexts``. Writing a 151number (``N``) to the file creates the number of child directories named as 152``0`` to ``N-1``. Each directory represents each monitoring context. At the 153moment, only one context per kdamond is supported, so only ``0`` or ``1`` can 154be written to the file. 155 156.. _sysfs_contexts: 157 158contexts/<N>/ 159------------- 160 161In each context directory, two files (``avail_operations`` and ``operations``) 162and three directories (``monitoring_attrs``, ``targets``, and ``schemes``) 163exist. 164 165DAMON supports multiple types of monitoring operations, including those for 166virtual address space and the physical address space. You can get the list of 167available monitoring operations set on the currently running kernel by reading 168``avail_operations`` file. Based on the kernel configuration, the file will 169list some or all of below keywords. 170 171 - vaddr: Monitor virtual address spaces of specific processes 172 - fvaddr: Monitor fixed virtual address ranges 173 - paddr: Monitor the physical address space of the system 174 175Please refer to :ref:`regions sysfs directory <sysfs_regions>` for detailed 176differences between the operations sets in terms of the monitoring target 177regions. 178 179You can set and get what type of monitoring operations DAMON will use for the 180context by writing one of the keywords listed in ``avail_operations`` file and 181reading from the ``operations`` file. 182 183.. _sysfs_monitoring_attrs: 184 185contexts/<N>/monitoring_attrs/ 186------------------------------ 187 188Files for specifying attributes of the monitoring including required quality 189and efficiency of the monitoring are in ``monitoring_attrs`` directory. 190Specifically, two directories, ``intervals`` and ``nr_regions`` exist in this 191directory. 192 193Under ``intervals`` directory, three files for DAMON's sampling interval 194(``sample_us``), aggregation interval (``aggr_us``), and update interval 195(``update_us``) exist. You can set and get the values in micro-seconds by 196writing to and reading from the files. 197 198Under ``nr_regions`` directory, two files for the lower-bound and upper-bound 199of DAMON's monitoring regions (``min`` and ``max``, respectively), which 200controls the monitoring overhead, exist. You can set and get the values by 201writing to and rading from the files. 202 203For more details about the intervals and monitoring regions range, please refer 204to the Design document (:doc:`/mm/damon/design`). 205 206contexts/<N>/targets/ 207--------------------- 208 209In the beginning, this directory has only one file, ``nr_targets``. Writing a 210number (``N``) to the file creates the number of child directories named ``0`` 211to ``N-1``. Each directory represents each monitoring target. 212 213targets/<N>/ 214------------ 215 216In each target directory, one file (``pid_target``) and one directory 217(``regions``) exist. 218 219If you wrote ``vaddr`` to the ``contexts/<N>/operations``, each target should 220be a process. You can specify the process to DAMON by writing the pid of the 221process to the ``pid_target`` file. 222 223.. _sysfs_regions: 224 225targets/<N>/regions 226------------------- 227 228When ``vaddr`` monitoring operations set is being used (``vaddr`` is written to 229the ``contexts/<N>/operations`` file), DAMON automatically sets and updates the 230monitoring target regions so that entire memory mappings of target processes 231can be covered. However, users could want to set the initial monitoring region 232to specific address ranges. 233 234In contrast, DAMON do not automatically sets and updates the monitoring target 235regions when ``fvaddr`` or ``paddr`` monitoring operations sets are being used 236(``fvaddr`` or ``paddr`` have written to the ``contexts/<N>/operations``). 237Therefore, users should set the monitoring target regions by themselves in the 238cases. 239 240For such cases, users can explicitly set the initial monitoring target regions 241as they want, by writing proper values to the files under this directory. 242 243In the beginning, this directory has only one file, ``nr_regions``. Writing a 244number (``N``) to the file creates the number of child directories named ``0`` 245to ``N-1``. Each directory represents each initial monitoring target region. 246 247regions/<N>/ 248------------ 249 250In each region directory, you will find two files (``start`` and ``end``). You 251can set and get the start and end addresses of the initial monitoring target 252region by writing to and reading from the files, respectively. 253 254Each region should not overlap with others. ``end`` of directory ``N`` should 255be equal or smaller than ``start`` of directory ``N+1``. 256 257contexts/<N>/schemes/ 258--------------------- 259 260The directory for DAMON-based Operation Schemes (:ref:`DAMOS 261<damon_design_damos>`). Users can get and set the schemes by reading from and 262writing to files under this directory. 263 264In the beginning, this directory has only one file, ``nr_schemes``. Writing a 265number (``N``) to the file creates the number of child directories named ``0`` 266to ``N-1``. Each directory represents each DAMON-based operation scheme. 267 268schemes/<N>/ 269------------ 270 271In each scheme directory, five directories (``access_pattern``, ``quotas``, 272``watermarks``, ``filters``, ``stats``, and ``tried_regions``) and one file 273(``action``) exist. 274 275The ``action`` file is for setting and getting the scheme's :ref:`action 276<damon_design_damos_action>`. The keywords that can be written to and read 277from the file and their meaning are as below. 278 279Note that support of each action depends on the running DAMON operations set 280:ref:`implementation <sysfs_contexts>`. 281 282 - ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED``. 283 Supported by ``vaddr`` and ``fvaddr`` operations set. 284 - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``. 285 Supported by ``vaddr`` and ``fvaddr`` operations set. 286 - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT``. 287 Supported by ``vaddr``, ``fvaddr`` and ``paddr`` operations set. 288 - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``. 289 Supported by ``vaddr`` and ``fvaddr`` operations set. 290 - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``. 291 Supported by ``vaddr`` and ``fvaddr`` operations set. 292 - ``lru_prio``: Prioritize the region on its LRU lists. 293 Supported by ``paddr`` operations set. 294 - ``lru_deprio``: Deprioritize the region on its LRU lists. 295 Supported by ``paddr`` operations set. 296 - ``stat``: Do nothing but count the statistics. 297 Supported by all operations sets. 298 299schemes/<N>/access_pattern/ 300--------------------------- 301 302The directory for the target access :ref:`pattern 303<damon_design_damos_access_pattern>` of the given DAMON-based operation scheme. 304 305Under the ``access_pattern`` directory, three directories (``sz``, 306``nr_accesses``, and ``age``) each having two files (``min`` and ``max``) 307exist. You can set and get the access pattern for the given scheme by writing 308to and reading from the ``min`` and ``max`` files under ``sz``, 309``nr_accesses``, and ``age`` directories, respectively. 310 311schemes/<N>/quotas/ 312------------------- 313 314The directory for the :ref:`quotas <damon_design_damos_quotas>` of the given 315DAMON-based operation scheme. 316 317Under ``quotas`` directory, three files (``ms``, ``bytes``, 318``reset_interval_ms``) and one directory (``weights``) having three files 319(``sz_permil``, ``nr_accesses_permil``, and ``age_permil``) in it exist. 320 321You can set the ``time quota`` in milliseconds, ``size quota`` in bytes, and 322``reset interval`` in milliseconds by writing the values to the three files, 323respectively. You can also set the :ref:`prioritization weights 324<damon_design_damos_quotas_prioritization>` for size, access frequency, and age 325in per-thousand unit by writing the values to the three files under the 326``weights`` directory. 327 328schemes/<N>/watermarks/ 329----------------------- 330 331The directory for the :ref:`watermarks <damon_design_damos_watermarks>` of the 332given DAMON-based operation scheme. 333 334Under the watermarks directory, five files (``metric``, ``interval_us``, 335``high``, ``mid``, and ``low``) for setting the metric, the time interval 336between check of the metric, and the three watermarks exist. You can set and 337get the five values by writing to the files, respectively. 338 339Keywords and meanings of those that can be written to the ``metric`` file are 340as below. 341 342 - none: Ignore the watermarks 343 - free_mem_rate: System's free memory rate (per thousand) 344 345The ``interval`` should written in microseconds unit. 346 347schemes/<N>/filters/ 348-------------------- 349 350The directory for the :ref:`filters <damon_design_damos_filters>` of the given 351DAMON-based operation scheme. 352 353In the beginning, this directory has only one file, ``nr_filters``. Writing a 354number (``N``) to the file creates the number of child directories named ``0`` 355to ``N-1``. Each directory represents each filter. The filters are evaluated 356in the numeric order. 357 358Each filter directory contains three files, namely ``type``, ``matcing``, and 359``memcg_path``. You can write one of two special keywords, ``anon`` for 360anonymous pages, or ``memcg`` for specific memory cgroup filtering. In case of 361the memory cgroup filtering, you can specify the memory cgroup of the interest 362by writing the path of the memory cgroup from the cgroups mount point to 363``memcg_path`` file. You can write ``Y`` or ``N`` to ``matching`` file to 364filter out pages that does or does not match to the type, respectively. Then, 365the scheme's action will not be applied to the pages that specified to be 366filtered out. 367 368For example, below restricts a DAMOS action to be applied to only non-anonymous 369pages of all memory cgroups except ``/having_care_already``.:: 370 371 # echo 2 > nr_filters 372 # # filter out anonymous pages 373 echo anon > 0/type 374 echo Y > 0/matching 375 # # further filter out all cgroups except one at '/having_care_already' 376 echo memcg > 1/type 377 echo /having_care_already > 1/memcg_path 378 echo N > 1/matching 379 380Note that filters are currently supported only when ``paddr`` 381`implementation <sysfs_contexts>` is being used. 382 383.. _sysfs_schemes_stats: 384 385schemes/<N>/stats/ 386------------------ 387 388DAMON counts the total number and bytes of regions that each scheme is tried to 389be applied, the two numbers for the regions that each scheme is successfully 390applied, and the total number of the quota limit exceeds. This statistics can 391be used for online analysis or tuning of the schemes. 392 393The statistics can be retrieved by reading the files under ``stats`` directory 394(``nr_tried``, ``sz_tried``, ``nr_applied``, ``sz_applied``, and 395``qt_exceeds``), respectively. The files are not updated in real time, so you 396should ask DAMON sysfs interface to updte the content of the files for the 397stats by writing a special keyword, ``update_schemes_stats`` to the relevant 398``kdamonds/<N>/state`` file. 399 400.. _sysfs_schemes_tried_regions: 401 402schemes/<N>/tried_regions/ 403-------------------------- 404 405When a special keyword, ``update_schemes_tried_regions``, is written to the 406relevant ``kdamonds/<N>/state`` file, DAMON creates directories named integer 407starting from ``0`` under this directory. Each directory contains files 408exposing detailed information about each of the memory region that the 409corresponding scheme's ``action`` has tried to be applied under this directory, 410during next :ref:`aggregation interval <sysfs_monitoring_attrs>`. The 411information includes address range, ``nr_accesses``, and ``age`` of the region. 412 413The directories will be removed when another special keyword, 414``clear_schemes_tried_regions``, is written to the relevant 415``kdamonds/<N>/state`` file. 416 417tried_regions/<N>/ 418------------------ 419 420In each region directory, you will find four files (``start``, ``end``, 421``nr_accesses``, and ``age``). Reading the files will show the start and end 422addresses, ``nr_accesses``, and ``age`` of the region that corresponding 423DAMON-based operation scheme ``action`` has tried to be applied. 424 425Example 426~~~~~~~ 427 428Below commands applies a scheme saying "If a memory region of size in [4KiB, 4298KiB] is showing accesses per aggregate interval in [0, 5] for aggregate 430interval in [10, 20], page out the region. For the paging out, use only up to 43110ms per second, and also don't page out more than 1GiB per second. Under the 432limitation, page out memory regions having longer age first. Also, check the 433free memory rate of the system every 5 seconds, start the monitoring and paging 434out when the free memory rate becomes lower than 50%, but stop it if the free 435memory rate becomes larger than 60%, or lower than 30%". :: 436 437 # cd <sysfs>/kernel/mm/damon/admin 438 # # populate directories 439 # echo 1 > kdamonds/nr_kdamonds; echo 1 > kdamonds/0/contexts/nr_contexts; 440 # echo 1 > kdamonds/0/contexts/0/schemes/nr_schemes 441 # cd kdamonds/0/contexts/0/schemes/0 442 # # set the basic access pattern and the action 443 # echo 4096 > access_pattern/sz/min 444 # echo 8192 > access_pattern/sz/max 445 # echo 0 > access_pattern/nr_accesses/min 446 # echo 5 > access_pattern/nr_accesses/max 447 # echo 10 > access_pattern/age/min 448 # echo 20 > access_pattern/age/max 449 # echo pageout > action 450 # # set quotas 451 # echo 10 > quotas/ms 452 # echo $((1024*1024*1024)) > quotas/bytes 453 # echo 1000 > quotas/reset_interval_ms 454 # # set watermark 455 # echo free_mem_rate > watermarks/metric 456 # echo 5000000 > watermarks/interval_us 457 # echo 600 > watermarks/high 458 # echo 500 > watermarks/mid 459 # echo 300 > watermarks/low 460 461Please note that it's highly recommended to use user space tools like `damo 462<https://github.com/awslabs/damo>`_ rather than manually reading and writing 463the files as above. Above is only for an example. 464 465.. _debugfs_interface: 466 467debugfs Interface (DEPRECATED!) 468=============================== 469 470.. note:: 471 472 THIS IS DEPRECATED! 473 474 DAMON debugfs interface is deprecated, so users should move to the 475 :ref:`sysfs interface <sysfs_interface>`. If you depend on this and cannot 476 move, please report your usecase to damon@lists.linux.dev and 477 linux-mm@kvack.org. 478 479DAMON exports eight files, ``attrs``, ``target_ids``, ``init_regions``, 480``schemes``, ``monitor_on``, ``kdamond_pid``, ``mk_contexts`` and 481``rm_contexts`` under its debugfs directory, ``<debugfs>/damon/``. 482 483 484Attributes 485---------- 486 487Users can get and set the ``sampling interval``, ``aggregation interval``, 488``update interval``, and min/max number of monitoring target regions by 489reading from and writing to the ``attrs`` file. To know about the monitoring 490attributes in detail, please refer to the :doc:`/mm/damon/design`. For 491example, below commands set those values to 5 ms, 100 ms, 1,000 ms, 10 and 4921000, and then check it again:: 493 494 # cd <debugfs>/damon 495 # echo 5000 100000 1000000 10 1000 > attrs 496 # cat attrs 497 5000 100000 1000000 10 1000 498 499 500Target IDs 501---------- 502 503Some types of address spaces supports multiple monitoring target. For example, 504the virtual memory address spaces monitoring can have multiple processes as the 505monitoring targets. Users can set the targets by writing relevant id values of 506the targets to, and get the ids of the current targets by reading from the 507``target_ids`` file. In case of the virtual address spaces monitoring, the 508values should be pids of the monitoring target processes. For example, below 509commands set processes having pids 42 and 4242 as the monitoring targets and 510check it again:: 511 512 # cd <debugfs>/damon 513 # echo 42 4242 > target_ids 514 # cat target_ids 515 42 4242 516 517Users can also monitor the physical memory address space of the system by 518writing a special keyword, "``paddr\n``" to the file. Because physical address 519space monitoring doesn't support multiple targets, reading the file will show a 520fake value, ``42``, as below:: 521 522 # cd <debugfs>/damon 523 # echo paddr > target_ids 524 # cat target_ids 525 42 526 527Note that setting the target ids doesn't start the monitoring. 528 529 530Initial Monitoring Target Regions 531--------------------------------- 532 533In case of the virtual address space monitoring, DAMON automatically sets and 534updates the monitoring target regions so that entire memory mappings of target 535processes can be covered. However, users can want to limit the monitoring 536region to specific address ranges, such as the heap, the stack, or specific 537file-mapped area. Or, some users can know the initial access pattern of their 538workloads and therefore want to set optimal initial regions for the 'adaptive 539regions adjustment'. 540 541In contrast, DAMON do not automatically sets and updates the monitoring target 542regions in case of physical memory monitoring. Therefore, users should set the 543monitoring target regions by themselves. 544 545In such cases, users can explicitly set the initial monitoring target regions 546as they want, by writing proper values to the ``init_regions`` file. The input 547should be a sequence of three integers separated by white spaces that represent 548one region in below form.:: 549 550 <target idx> <start address> <end address> 551 552The ``target idx`` should be the index of the target in ``target_ids`` file, 553starting from ``0``, and the regions should be passed in address order. For 554example, below commands will set a couple of address ranges, ``1-100`` and 555``100-200`` as the initial monitoring target region of pid 42, which is the 556first one (index ``0``) in ``target_ids``, and another couple of address 557ranges, ``20-40`` and ``50-100`` as that of pid 4242, which is the second one 558(index ``1``) in ``target_ids``.:: 559 560 # cd <debugfs>/damon 561 # cat target_ids 562 42 4242 563 # echo "0 1 100 \ 564 0 100 200 \ 565 1 20 40 \ 566 1 50 100" > init_regions 567 568Note that this sets the initial monitoring target regions only. In case of 569virtual memory monitoring, DAMON will automatically updates the boundary of the 570regions after one ``update interval``. Therefore, users should set the 571``update interval`` large enough in this case, if they don't want the 572update. 573 574 575Schemes 576------- 577 578Users can get and set the DAMON-based operation :ref:`schemes 579<damon_design_damos>` by reading from and writing to ``schemes`` debugfs file. 580Reading the file also shows the statistics of each scheme. To the file, each 581of the schemes should be represented in each line in below form:: 582 583 <target access pattern> <action> <quota> <watermarks> 584 585You can disable schemes by simply writing an empty string to the file. 586 587Target Access Pattern 588~~~~~~~~~~~~~~~~~~~~~ 589 590The target access :ref:`pattern <damon_design_damos_access_pattern>` of the 591scheme. The ``<target access pattern>`` is constructed with three ranges in 592below form:: 593 594 min-size max-size min-acc max-acc min-age max-age 595 596Specifically, bytes for the size of regions (``min-size`` and ``max-size``), 597number of monitored accesses per aggregate interval for access frequency 598(``min-acc`` and ``max-acc``), number of aggregate intervals for the age of 599regions (``min-age`` and ``max-age``) are specified. Note that the ranges are 600closed interval. 601 602Action 603~~~~~~ 604 605The ``<action>`` is a predefined integer for memory management :ref:`actions 606<damon_design_damos_action>`. The supported numbers and their meanings are as 607below. 608 609 - 0: Call ``madvise()`` for the region with ``MADV_WILLNEED``. Ignored if 610 ``target`` is ``paddr``. 611 - 1: Call ``madvise()`` for the region with ``MADV_COLD``. Ignored if 612 ``target`` is ``paddr``. 613 - 2: Call ``madvise()`` for the region with ``MADV_PAGEOUT``. 614 - 3: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``. Ignored if 615 ``target`` is ``paddr``. 616 - 4: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``. Ignored if 617 ``target`` is ``paddr``. 618 - 5: Do nothing but count the statistics 619 620Quota 621~~~~~ 622 623Users can set the :ref:`quotas <damon_design_damos_quotas>` of the given scheme 624via the ``<quota>`` in below form:: 625 626 <ms> <sz> <reset interval> <priority weights> 627 628This makes DAMON to try to use only up to ``<ms>`` milliseconds for applying 629the action to memory regions of the ``target access pattern`` within the 630``<reset interval>`` milliseconds, and to apply the action to only up to 631``<sz>`` bytes of memory regions within the ``<reset interval>``. Setting both 632``<ms>`` and ``<sz>`` zero disables the quota limits. 633 634For the :ref:`prioritization <damon_design_damos_quotas_prioritization>`, users 635can set the weights for the three properties in ``<priority weights>`` in below 636form:: 637 638 <size weight> <access frequency weight> <age weight> 639 640Watermarks 641~~~~~~~~~~ 642 643Users can specify :ref:`watermarks <damon_design_damos_watermarks>` of the 644given scheme via ``<watermarks>`` in below form:: 645 646 <metric> <check interval> <high mark> <middle mark> <low mark> 647 648``<metric>`` is a predefined integer for the metric to be checked. The 649supported numbers and their meanings are as below. 650 651 - 0: Ignore the watermarks 652 - 1: System's free memory rate (per thousand) 653 654The value of the metric is checked every ``<check interval>`` microseconds. 655 656If the value is higher than ``<high mark>`` or lower than ``<low mark>``, the 657scheme is deactivated. If the value is lower than ``<mid mark>``, the scheme 658is activated. 659 660.. _damos_stats: 661 662Statistics 663~~~~~~~~~~ 664 665It also counts the total number and bytes of regions that each scheme is tried 666to be applied, the two numbers for the regions that each scheme is successfully 667applied, and the total number of the quota limit exceeds. This statistics can 668be used for online analysis or tuning of the schemes. 669 670The statistics can be shown by reading the ``schemes`` file. Reading the file 671will show each scheme you entered in each line, and the five numbers for the 672statistics will be added at the end of each line. 673 674Example 675~~~~~~~ 676 677Below commands applies a scheme saying "If a memory region of size in [4KiB, 6788KiB] is showing accesses per aggregate interval in [0, 5] for aggregate 679interval in [10, 20], page out the region. For the paging out, use only up to 68010ms per second, and also don't page out more than 1GiB per second. Under the 681limitation, page out memory regions having longer age first. Also, check the 682free memory rate of the system every 5 seconds, start the monitoring and paging 683out when the free memory rate becomes lower than 50%, but stop it if the free 684memory rate becomes larger than 60%, or lower than 30%".:: 685 686 # cd <debugfs>/damon 687 # scheme="4096 8192 0 5 10 20 2" # target access pattern and action 688 # scheme+=" 10 $((1024*1024*1024)) 1000" # quotas 689 # scheme+=" 0 0 100" # prioritization weights 690 # scheme+=" 1 5000000 600 500 300" # watermarks 691 # echo "$scheme" > schemes 692 693 694Turning On/Off 695-------------- 696 697Setting the files as described above doesn't incur effect unless you explicitly 698start the monitoring. You can start, stop, and check the current status of the 699monitoring by writing to and reading from the ``monitor_on`` file. Writing 700``on`` to the file starts the monitoring of the targets with the attributes. 701Writing ``off`` to the file stops those. DAMON also stops if every target 702process is terminated. Below example commands turn on, off, and check the 703status of DAMON:: 704 705 # cd <debugfs>/damon 706 # echo on > monitor_on 707 # echo off > monitor_on 708 # cat monitor_on 709 off 710 711Please note that you cannot write to the above-mentioned debugfs files while 712the monitoring is turned on. If you write to the files while DAMON is running, 713an error code such as ``-EBUSY`` will be returned. 714 715 716Monitoring Thread PID 717--------------------- 718 719DAMON does requested monitoring with a kernel thread called ``kdamond``. You 720can get the pid of the thread by reading the ``kdamond_pid`` file. When the 721monitoring is turned off, reading the file returns ``none``. :: 722 723 # cd <debugfs>/damon 724 # cat monitor_on 725 off 726 # cat kdamond_pid 727 none 728 # echo on > monitor_on 729 # cat kdamond_pid 730 18594 731 732 733Using Multiple Monitoring Threads 734--------------------------------- 735 736One ``kdamond`` thread is created for each monitoring context. You can create 737and remove monitoring contexts for multiple ``kdamond`` required use case using 738the ``mk_contexts`` and ``rm_contexts`` files. 739 740Writing the name of the new context to the ``mk_contexts`` file creates a 741directory of the name on the DAMON debugfs directory. The directory will have 742DAMON debugfs files for the context. :: 743 744 # cd <debugfs>/damon 745 # ls foo 746 # ls: cannot access 'foo': No such file or directory 747 # echo foo > mk_contexts 748 # ls foo 749 # attrs init_regions kdamond_pid schemes target_ids 750 751If the context is not needed anymore, you can remove it and the corresponding 752directory by putting the name of the context to the ``rm_contexts`` file. :: 753 754 # echo foo > rm_contexts 755 # ls foo 756 # ls: cannot access 'foo': No such file or directory 757 758Note that ``mk_contexts``, ``rm_contexts``, and ``monitor_on`` files are in the 759root directory only. 760 761 762.. _tracepoint: 763 764Tracepoint for Monitoring Results 765================================= 766 767DAMON provides the monitoring results via a tracepoint, 768``damon:damon_aggregated``. While the monitoring is turned on, you could 769record the tracepoint events and show results using tracepoint supporting tools 770like ``perf``. For example:: 771 772 # echo on > monitor_on 773 # perf record -e damon:damon_aggregated & 774 # sleep 5 775 # kill 9 $(pidof perf) 776 # echo off > monitor_on 777 # perf script 778