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1 .. SPDX-License-Identifier: GPL-2.0
13 The monitoring-related information including the monitoring request
14 specification and DAMON-based operation schemes are stored in a data structure
19 To know how user-space can do the configurations and start/stop DAMON, refer to
28 - :ref:`Operations Set <damon_operations_set>`: Implements fundamental
30 address-space and available set of software/hardware primitives,
31 - :ref:`Core <damon_core_logic>`: Implements core logics including monitoring
32 overhead/accuracy control and access-aware system operations on top of the
34 - :ref:`Modules <damon_modules>`: Implements kernel modules for various
49 monitoring are address-space dependent.
73 - vaddr: Monitor virtual address spaces of specific processes
74 - fvaddr: Monitor fixed virtual address ranges
75 - paddr: Monitor the physical address space of the system
77 To know how user-space can do the configuration via :ref:`DAMON sysfs interface
84 VMA-based Target Address Range Construction
85 -------------------------------------------
95 Only small parts in the super-huge virtual address space of the processes are
107 heap and the uppermost mmap()-ed region, and the gap between the lowermost
108 mmap()-ed region and the stack in most of the cases. Because these gaps are
110 to make a reasonable trade-off. Below shows this in detail::
114 <uppermost mmap()-ed region>
115 (small mmap()-ed regions and munmap()-ed regions)
116 <lowermost mmap()-ed region>
121 PTE Accessed-bit Based Access Check
122 -----------------------------------
125 Accessed-bit for basic access checks. Only one difference is the way of
127 implementation for the virtual address walks the page table for the target task
128 of the address, the implementation for the physical address walks every page
132 subsystems using the Accessed bits, namely Idle page tracking and the reclaim
133 logic. DAMON does nothing to avoid disturbing Idle page tracking, so handling
135 conflict with the reclaim logic using ``PG_idle`` and ``PG_young`` page flags,
136 as Idle page tracking does.
147 ----------
154 To know how user-space can set the attributes via :ref:`DAMON sysfs interface
165 access to each page per ``sampling interval`` and aggregates the results. In
166 other words, counts the number of the accesses to each page. After each
169 clears the results. This can be described in below simple pseudo-code::
172 for page in monitoring_target:
173 if accessed(page):
174 nr_accesses[page] += 1
178 for page in monitoring_target:
179 nr_accesses[page] = 0
188 Region Based Sampling
194 one page in the region is required to be checked. Thus, for each ``sampling
195 interval``, DAMON randomly picks one page in each region, waits for one
196 ``sampling interval``, checks whether the page is accessed meanwhile, and
200 minimum and the maximum number of regions for the trade-off.
215 adaptively merges and splits each region based on their access frequency.
223 threshold until the upper-limit of the number of regions is met, or the
227 three regions if the total number of regions will not exceed the user-specified
230 In this way, DAMON provides its best-effort quality and minimal overhead while
231 keeping the bounds users set for their trade-off.
241 understanding of the access pattern. For example, page placement algorithm
255 be hot-plugged.
259 and applies it to monitoring operations-related data structures such as the
260 abstracted monitoring target memory area only for each of a user-specified time
263 User-space can get the monitoring results via DAMON sysfs interface and/or
298 intensiveness of the workload. The user should tune the interval based on the
308 undistinguishable based on access pattern, and therefore the results will be
316 Refer to below documents for an example tuning based on the above guide.
327 -----------------
329 One common purpose of data access monitoring is access-aware system efficiency
339 One straightforward approach for such schemes would be profile-guided
356 works, DAMON provides a feature called Data Access Monitoring-based Operation
359 the access pattern of interest, and applies the user-desired operation actions
360 to the regions, for every user-specified time interval called
363 To know how user-space can set ``apply_interval`` via :ref:`DAMON sysfs
390 - ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED``.
392 - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``.
394 - ``pageout``: Reclaim the region.
396 - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``.
398 - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``.
400 - ``lru_prio``: Prioritize the region on its LRU lists.
402 - ``lru_deprio``: Deprioritize the region on its LRU lists.
404 - ``migrate_hot``: Migrate the regions prioritizing warmer regions.
406 - ``migrate_cold``: Migrate the regions prioritizing colder regions.
408 - ``stat``: Do nothing but count the statistics.
415 To know how user-space can set the action via :ref:`DAMON sysfs interface
432 To know how user-space can set the access pattern via :ref:`DAMON sysfs
442 DAMOS upper-bound overhead control feature. DAMOS could incur high overhead if
450 To mitigate that situation, DAMOS provides an upper-bound overhead control
453 the action can be applied within a user-specified time duration.
455 To know how user-space can set the basic quotas via :ref:`DAMON sysfs interface
471 rarely accessed (colder) memory regions would be prioritized for page-out
473 page collapse scheme action. Hence, the prioritization mechanisms for each
486 To know how user-space can set the prioritization weights via :ref:`DAMON sysfs
493 Aim-oriented Feedback-driven Auto-tuning
496 Automatic feedback-driven quota tuning. Instead of setting the absolute quota
504 ``target_value``, and ``current_value``. The auto-tuning mechanism tries to
508 - ``user_input``: User-provided value. Users could use any metric that they
514 - ``some_mem_psi_us``: System-wide ``some`` memory pressure stall information
517 set by users at the initial time. In other words, DAMOS does self-feedback.
519 To know how user-space can set the tuning goal metric, the target value, and/or
545 To know how user-space can set the watermarks via :ref:`DAMON sysfs interface
555 Non-access pattern-based target memory regions filtering. If users run
556 self-written programs or have good profiling tools, they could know something
560 have a list of latency-critical processes.
566 - a type of memory (``type``),
567 - whether it is for the memory of the type or all except the type
569 - whether it is to allow (include) or reject (exclude) applying
579 another filter for rejecting young pages are installed in the order. If a page
580 of a region that eligible to apply the scheme's action is an anonymous page,
581 the scheme's action will be applied to the page regardless of whether it is
582 young or not, since it matches with the first allow-filter. If the page is
584 second reject-filter blocks it. If the page is neither anonymous nor young,
585 the page will pass through the filters evaluation stage since there is no
586 matching filter, and the action will be applied to the page.
589 filter-allowed or filters evaluation stage passed. It means that installing
590 allow-filters at the end of the list makes no practical change but only
591 filters-checking overhead.
596 case of the core layer-handled filters, the memory regions that excluded by the
598 a memory regions is filtered by an operations set layer-handled filter, it is
603 - anonymous page
604 - Applied to pages that containing data that not stored in files.
605 - Handled by operations set layer. Supported by only ``paddr`` set.
606 - memory cgroup
607 - Applied to pages that belonging to a given cgroup.
608 - Handled by operations set layer. Supported by only ``paddr`` set.
609 - young page
610 - Applied to pages that are accessed after the last access check from the
612 - Handled by operations set layer. Supported by only ``paddr`` set.
613 - address range
614 - Applied to pages that belonging to a given address range.
615 - Handled by the core logic.
616 - DAMON monitoring target
617 - Applied to pages that belonging to a given DAMON monitoring target.
618 - Handled by the core logic.
620 To know how user-space can set the watermarks via :ref:`DAMON sysfs interface
635 - ``nr_tried``: Total number of regions that the scheme is tried to be applied.
636 - ``sz_trtied``: Total size of regions that the scheme is tried to be applied.
637 - ``sz_ops_filter_passed``: Total bytes that passed operations set
638 layer-handled DAMOS filters.
639 - ``nr_applied``: Total number of regions that the scheme is applied.
640 - ``sz_applied``: Total size of regions that the scheme is applied.
641 - ``qt_exceeds``: Total number of times the quota of the scheme has exceeded.
663 To know how user-space can read the stats via :ref:`DAMON sysfs interface
680 ---------------------------------
682 The programming interface for kernel space data access-aware applications.
685 access-aware applications using DAMON's core features. For this, DAMON exposes
700 for general purpose DAMON control and special purpose data access-aware system
702 user space. The user space can build their efficient data access-aware
707 --------------------------------------
716 requested via the DAMON API, and return the results to the user-space.
720 user space tools. One such Python-written user space tool is available at
723 (https://packages.fedoraproject.org/pkgs/python-damo/damo/).
730 Special-Purpose Access-aware Kernel Modules
731 -------------------------------------------
736 runtime. For each special-purpose system-wide data access-aware system
739 extended for boot-time and even compile time control. Default values of DAMON
747 (:doc:`/admin-guide/mm/damon/reclaim` and
748 :doc:`/admin-guide/mm/damon/lru_sort`).