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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 Based on the manual tuning guide, DAMON provides more intuitive knob-based
320 Refer to below documents for an example tuning based on the above guide.
330 Monitoring Intervals Auto-tuning
334 interval`` based on the :ref:`the tuning guide idea
338 DAMON-observed access events to the theoretical maximum amount of the events
342 The DAMON-observed access events are calculated in byte granularity based on
366 That is, assumes 4% (20% of 20%) DAMON-observed access events ratio (source)
369 To know how user-space can use this feature via :ref:`DAMON sysfs interface
377 -----------------
379 One common purpose of data access monitoring is access-aware system efficiency
389 One straightforward approach for such schemes would be profile-guided
406 works, DAMON provides a feature called Data Access Monitoring-based Operation
409 the access pattern of interest, and applies the user-desired operation actions
410 to the regions, for every user-specified time interval called
413 To know how user-space can set ``apply_interval`` via :ref:`DAMON sysfs
440 - ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED``.
442 - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``.
444 - ``pageout``: Reclaim the region.
446 - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``.
448 - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``.
450 - ``lru_prio``: Prioritize the region on its LRU lists.
452 - ``lru_deprio``: Deprioritize the region on its LRU lists.
454 - ``migrate_hot``: Migrate the regions prioritizing warmer regions.
456 - ``migrate_cold``: Migrate the regions prioritizing colder regions.
458 - ``stat``: Do nothing but count the statistics.
465 To know how user-space can set the action via :ref:`DAMON sysfs interface
482 To know how user-space can set the access pattern via :ref:`DAMON sysfs
492 DAMOS upper-bound overhead control feature. DAMOS could incur high overhead if
500 To mitigate that situation, DAMOS provides an upper-bound overhead control
503 the action can be applied within a user-specified time duration.
505 To know how user-space can set the basic quotas via :ref:`DAMON sysfs interface
521 rarely accessed (colder) memory regions would be prioritized for page-out
523 page collapse scheme action. Hence, the prioritization mechanisms for each
536 To know how user-space can set the prioritization weights via :ref:`DAMON sysfs
543 Aim-oriented Feedback-driven Auto-tuning
546 Automatic feedback-driven quota tuning. Instead of setting the absolute quota
554 ``target_value``, ``current_value`` and ``nid``. The auto-tuning mechanism
558 - ``user_input``: User-provided value. Users could use any metric that they
564 - ``some_mem_psi_us``: System-wide ``some`` memory pressure stall information
567 set by users at the initial time. In other words, DAMOS does self-feedback.
568 - ``node_mem_used_bp``: Specific NUMA node's used memory ratio in bp (1/10,000).
569 - ``node_mem_free_bp``: Specific NUMA node's free memory ratio in bp (1/10,000).
574 To know how user-space can set the tuning goal metric, the target value, and/or
600 To know how user-space can set the watermarks via :ref:`DAMON sysfs interface
610 Non-access pattern-based target memory regions filtering. If users run
611 self-written programs or have good profiling tools, they could know something
615 have a list of latency-critical processes.
621 - a type of memory (``type``),
622 - whether it is for the memory of the type or all except the type
624 - whether it is to allow (include) or reject (exclude) applying
630 case of the core layer-handled filters, the memory regions that excluded by the
632 a memory regions is filtered by an operations set layer-handled filter, it is
645 another filter for rejecting young pages are installed in the order. If a page
646 of a region that eligible to apply the scheme's action is an anonymous page,
647 the scheme's action will be applied to the page regardless of whether it is
648 young or not, since it matches with the first allow-filter. If the page is
650 second reject-filter blocks it. If the page is neither anonymous nor young,
651 the page will pass through the filters evaluation stage since there is no
652 matching filter, and the action will be applied to the page.
656 - Core layer handled
657 - addr
658 - Applied to pages that belonging to a given address range.
659 - target
660 - Applied to pages that belonging to a given DAMON monitoring target.
661 - Operations layer handled, supported by only ``paddr`` operations set.
662 - anon
663 - Applied to pages that containing data that not stored in files.
664 - active
665 - Applied to active pages.
666 - memcg
667 - Applied to pages that belonging to a given cgroup.
668 - young
669 - Applied to pages that are accessed after the last access check from the
671 - hugepage_size
672 - Applied to pages that managed in a given size range.
673 - unmapped
674 - Applied to pages that unmapped.
676 To know how user-space can set the filters via :ref:`DAMON sysfs interface
691 - ``nr_tried``: Total number of regions that the scheme is tried to be applied.
692 - ``sz_trtied``: Total size of regions that the scheme is tried to be applied.
693 - ``sz_ops_filter_passed``: Total bytes that passed operations set
694 layer-handled DAMOS filters.
695 - ``nr_applied``: Total number of regions that the scheme is applied.
696 - ``sz_applied``: Total size of regions that the scheme is applied.
697 - ``qt_exceeds``: Total number of times the quota of the scheme has exceeded.
719 To know how user-space can read the stats via :ref:`DAMON sysfs interface
736 ---------------------------------
738 The programming interface for kernel space data access-aware applications.
741 access-aware applications using DAMON's core features. For this, DAMON exposes
756 for general purpose DAMON control and special purpose data access-aware system
758 user space. The user space can build their efficient data access-aware
763 --------------------------------------
772 requested via the DAMON API, and return the results to the user-space.
776 user space tools. One such Python-written user space tool is available at
779 (https://packages.fedoraproject.org/pkgs/python-damo/damo/).
786 Special-Purpose Access-aware Kernel Modules
787 -------------------------------------------
792 runtime. For each special-purpose system-wide data access-aware system
795 extended for boot-time and even compile time control. Default values of DAMON
803 (:doc:`/admin-guide/mm/damon/reclaim` and
804 :doc:`/admin-guide/mm/damon/lru_sort`).