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diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst index 1bb69524a62e..ddc50db3afa4 100644 --- a/Documentation/mm/damon/design.rst +++ b/Documentation/mm/damon/design.rst @@ -16,71 +16,81 @@ called DAMON ``context``. DAMON executes each context with a kernel thread called ``kdamond``. Multiple kdamonds could run in parallel, for different types of monitoring. +To know how user-space can do the configurations and start/stop DAMON, refer to +:ref:`DAMON sysfs interface <sysfs_interface>` documentation. + Overall Architecture ==================== DAMON subsystem is configured with three layers including -- Operations Set: Implements fundamental operations for DAMON that depends on - the given monitoring target address-space and available set of - software/hardware primitives, -- Core: Implements core logics including monitoring overhead/accurach control - and access-aware system operations on top of the operations set layer, and -- Modules: Implements kernel modules for various purposes that provides - interfaces for the user space, on top of the core layer. +- :ref:`Operations Set <damon_operations_set>`: Implements fundamental + operations for DAMON that depends on the given monitoring target + address-space and available set of software/hardware primitives, +- :ref:`Core <damon_core_logic>`: Implements core logics including monitoring + overhead/accuracy control and access-aware system operations on top of the + operations set layer, and +- :ref:`Modules <damon_modules>`: Implements kernel modules for various + purposes that provides interfaces for the user space, on top of the core + layer. -Configurable Operations Set ---------------------------- +.. _damon_operations_set: -For data access monitoring and additional low level work, DAMON needs a set of -implementations for specific operations that are dependent on and optimized for -the given target address space. On the other hand, the accuracy and overhead -tradeoff mechanism, which is the core logic of DAMON, is in the pure logic -space. DAMON separates the two parts in different layers, namely DAMON -Operations Set and DAMON Core Logics Layers, respectively. It further defines -the interface between the layers to allow various operations sets to be -configured with the core logic. +Operations Set Layer +==================== -Due to this design, users can extend DAMON for any address space by configuring -the core logic to use the appropriate operations set. If any appropriate set -is unavailable, users can implement one on their own. +.. _damon_design_configurable_operations_set: -For example, physical memory, virtual memory, swap space, those for specific -processes, NUMA nodes, files, and backing memory devices would be supportable. -Also, if some architectures or devices supporting special optimized access -check primitives, those will be easily configurable. +For data access monitoring and additional low level work, DAMON needs a set of +implementations for specific operations that are dependent on and optimized for +the given target address space. For example, below two operations for access +monitoring are address-space dependent. +1. Identification of the monitoring target address range for the address space. +2. Access check of specific address range in the target space. -Programmable Modules --------------------- +DAMON consolidates these implementations in a layer called DAMON Operations +Set, and defines the interface between it and the upper layer. The upper layer +is dedicated for DAMON's core logics including the mechanism for control of the +monitoring accuracy and the overhead. -Core layer of DAMON is implemented as a framework, and exposes its application -programming interface to all kernel space components such as subsystems and -modules. For common use cases of DAMON, DAMON subsystem provides kernel -modules that built on top of the core layer using the API, which can be easily -used by the user space end users. +Hence, DAMON can easily be extended for any address space and/or available +hardware features by configuring the core logic to use the appropriate +operations set. If there is no available operations set for a given purpose, a +new operations set can be implemented following the interface between the +layers. +For example, physical memory, virtual memory, swap space, those for specific +processes, NUMA nodes, files, and backing memory devices would be supportable. +Also, if some architectures or devices support special optimized access check +features, those will be easily configurable. -Operations Set Layer -==================== +DAMON currently provides below three operation sets. Below two subsections +describe how those work. -The monitoring operations are defined in two parts: + - vaddr: Monitor virtual address spaces of specific processes + - fvaddr: Monitor fixed virtual address ranges + - paddr: Monitor the physical address space of the system -1. Identification of the monitoring target address range for the address space. -2. Access check of specific address range in the target space. +To know how user-space can do the configuration via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:`operations <sysfs_context>` file part of the +documentation. -DAMON currently provides the implementations of the operations for the physical -and virtual address spaces. Below two subsections describe how those work. + .. _damon_design_vaddr_target_regions_construction: VMA-based Target Address Range Construction ------------------------------------------- -This is only for the virtual address space monitoring operations -implementation. That for the physical address space simply asks users to -manually set the monitoring target address ranges. +A mechanism of ``vaddr`` DAMON operations set that automatically initializes +and updates the monitoring target address regions so that entire memory +mappings of the target processes can be covered. + +This mechanism is only for the ``vaddr`` operations set. In cases of +``fvaddr`` and ``paddr`` operation sets, users are asked to manually set the +monitoring target address ranges. Only small parts in the super-huge virtual address space of the processes are mapped to the physical memory and accessed. Thus, tracking the unmapped @@ -126,9 +136,12 @@ conflict with the reclaim logic using ``PG_idle`` and ``PG_young`` page flags, as Idle page tracking does. +.. _damon_core_logic: + Core Logics =========== +.. _damon_design_monitoring: Monitoring ---------- @@ -138,6 +151,10 @@ monitoring attributes, ``sampling interval``, ``aggregation interval``, ``update interval``, ``minimum number of regions``, and ``maximum number of regions``. +To know how user-space can set the attributes via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:`monitoring_attrs <sysfs_monitoring_attrs>` +part of the documentation. + Access Frequency Monitoring ~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -178,7 +195,7 @@ one page in the region is required to be checked. Thus, for each ``sampling interval``, DAMON randomly picks one page in each region, waits for one ``sampling interval``, checks whether the page is accessed meanwhile, and increases the access frequency counter of the region if so. The counter is -called ``nr_regions`` of the region. Therefore, the monitoring overhead is +called ``nr_accesses`` of the region. Therefore, the monitoring overhead is controllable by setting the number of regions. DAMON allows users to set the minimum and the maximum number of regions for the trade-off. @@ -186,6 +203,8 @@ This scheme, however, cannot preserve the quality of the output if the assumption is not guaranteed. +.. _damon_design_adaptive_regions_adjustment: + Adaptive Regions Adjustment ~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -195,11 +214,18 @@ the data access pattern can be dynamically changed. This will result in low monitoring quality. To keep the assumption as much as possible, DAMON adaptively merges and splits each region based on their access frequency. -For each ``aggregation interval``, it compares the access frequencies of -adjacent regions and merges those if the frequency difference is small. Then, -after it reports and clears the aggregated access frequency of each region, it -splits each region into two or three regions if the total number of regions -will not exceed the user-specified maximum number of regions after the split. +For each ``aggregation interval``, it compares the access frequencies +(``nr_accesses``) of adjacent regions. If the difference is small, and if the +sum of the two regions' sizes is smaller than the size of total regions divided +by the ``minimum number of regions``, DAMON merges the two regions. If the +resulting number of total regions is still higher than ``maximum number of +regions``, it repeats the merging with increasing access frequenceis difference +threshold until the upper-limit of the number of regions is met, or the +threshold becomes higher than possible maximum value (``aggregation interval`` +divided by ``sampling interval``). Then, after it reports and clears the +aggregated access frequency of each region, it splits each region into two or +three regions if the total number of regions will not exceed the user-specified +maximum number of regions after the split. In this way, DAMON provides its best-effort quality and minimal overhead while keeping the bounds users set for their trade-off. @@ -234,6 +260,116 @@ and applies it to monitoring operations-related data structures such as the abstracted monitoring target memory area only for each of a user-specified time interval (``update interval``). +User-space can get the monitoring results via DAMON sysfs interface and/or +tracepoints. For more details, please refer to the documentations for +:ref:`DAMOS tried regions <sysfs_schemes_tried_regions>` and :ref:`tracepoint`, +respectively. + + +.. _damon_design_monitoring_params_tuning_guide: + +Monitoring Parameters Tuning Guide +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In short, set ``aggregation interval`` to capture meaningful amount of accesses +for the purpose. The amount of accesses can be measured using ``nr_accesses`` +and ``age`` of regions in the aggregated monitoring results snapshot. The +default value of the interval, ``100ms``, turns out to be too short in many +cases. Set ``sampling interval`` proportional to ``aggregation interval``. By +default, ``1/20`` is recommended as the ratio. + +``Aggregation interval`` should be set as the time interval that the workload +can make an amount of accesses for the monitoring purpose, within the interval. +If the interval is too short, only small number of accesses are captured. As a +result, the monitoring results look everything is samely accessed only rarely. +For many purposes, that would be useless. If it is too long, however, the time +to converge regions with the :ref:`regions adjustment mechanism +<damon_design_adaptive_regions_adjustment>` can be too long, depending on the +time scale of the given purpose. This could happen if the workload is actually +making only rare accesses but the user thinks the amount of accesses for the +monitoring purpose too high. For such cases, the target amount of access to +capture per ``aggregation interval`` should carefully reconsidered. Also, note +that the captured amount of accesses is represented with not only +``nr_accesses``, but also ``age``. For example, even if every region on the +monitoring results show zero ``nr_accesses``, regions could still be +distinguished using ``age`` values as the recency information. + +Hence the optimum value of ``aggregation interval`` depends on the access +intensiveness of the workload. The user should tune the interval based on the +amount of access that captured on each aggregated snapshot of the monitoring +results. + +Note that the default value of the interval is 100 milliseconds, which is too +short in many cases, especially on large systems. + +``Sampling interval`` defines the resolution of each aggregation. If it is set +too large, monitoring results will look like every region was samely rarely +accessed, or samely frequently accessed. That is, regions become +undistinguishable based on access pattern, and therefore the results will be +useless in many use cases. If ``sampling interval`` is too small, it will not +degrade the resolution, but will increase the monitoring overhead. If it is +appropriate enough to provide a resolution of the monitoring results that +sufficient for the given purpose, it shouldn't be unnecessarily further +lowered. It is recommended to be set proportional to ``aggregation interval``. +By default, the ratio is set as ``1/20``, and it is still recommended. + +Based on the manual tuning guide, DAMON provides more intuitive knob-based +intervals auto tuning mechanism. Please refer to :ref:`the design document of +the feature <damon_design_monitoring_intervals_autotuning>` for detail. + +Refer to below documents for an example tuning based on the above guide. + +.. toctree:: + :maxdepth: 1 + + monitoring_intervals_tuning_example + + +.. _damon_design_monitoring_intervals_autotuning: + +Monitoring Intervals Auto-tuning +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +DAMON provides automatic tuning of the ``sampling interval`` and ``aggregation +interval`` based on the :ref:`the tuning guide idea +<damon_design_monitoring_params_tuning_guide>`. The tuning mechanism allows +users to set the aimed amount of access events to observe via DAMON within +given time interval. The target can be specified by the user as a ratio of +DAMON-observed access events to the theoretical maximum amount of the events +(``access_bp``) that measured within a given number of aggregations +(``aggrs``). + +The DAMON-observed access events are calculated in byte granularity based on +DAMON :ref:`region assumption <damon_design_region_based_sampling>`. For +example, if a region of size ``X`` bytes of ``Y`` ``nr_accesses`` is found, it +means ``X * Y`` access events are observed by DAMON. Theoretical maximum +access events for the region is calculated in same way, but replacing ``Y`` +with theoretical maximum ``nr_accesses``, which can be calculated as +``aggregation interval / sampling interval``. + +The mechanism calculates the ratio of access events for ``aggrs`` aggregations, +and increases or decrease the ``sampleing interval`` and ``aggregation +interval`` in same ratio, if the observed access ratio is lower or higher than +the target, respectively. The ratio of the intervals change is decided in +proportion to the distance between current samples ratio and the target ratio. + +The user can further set the minimum and maximum ``sampling interval`` that can +be set by the tuning mechanism using two parameters (``min_sample_us`` and +``max_sample_us``). Because the tuning mechanism changes ``sampling interval`` +and ``aggregation interval`` in same ratio always, the minimum and maximum +``aggregation interval`` after each of the tuning changes can automatically set +together. + +The tuning is turned off by default, and need to be set explicitly by the user. +As a rule of thumbs and the Parreto principle, 4% access samples ratio target +is recommended. Note that Parreto principle (80/20 rule) has applied twice. +That is, assumes 4% (20% of 20%) DAMON-observed access events ratio (source) +to capture 64% (80% multipled by 80%) real access events (outcomes). + +To know how user-space can use this feature via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:`intervals_goal <sysfs_scheme>` part of +the documentation. + .. _damon_design_damos: @@ -274,6 +410,10 @@ the access pattern of interest, and applies the user-desired operation actions to the regions, for every user-specified time interval called ``apply_interval``. +To know how user-space can set ``apply_interval`` via :ref:`DAMON sysfs +interface <sysfs_interface>`, refer to :ref:`apply_interval_us <sysfs_scheme>` +part of the documentation. + .. _damon_design_damos_action: @@ -294,9 +434,37 @@ not mandated to support all actions of the list. Hence, the availability of specific DAMOS action depends on what operations set is selected to be used together. -Applying an action to a region is considered as changing the region's -characteristics. Hence, DAMOS resets the age of regions when an action is -applied to those. +The list of the supported actions, their meaning, and DAMON operations sets +that supports each action are as below. + + - ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``pageout``: Reclaim the region. + Supported by ``vaddr``, ``fvaddr`` and ``paddr`` operations set. + - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``. + Supported by ``vaddr`` and ``fvaddr`` operations set. + - ``lru_prio``: Prioritize the region on its LRU lists. + Supported by ``paddr`` operations set. + - ``lru_deprio``: Deprioritize the region on its LRU lists. + Supported by ``paddr`` operations set. + - ``migrate_hot``: Migrate the regions prioritizing warmer regions. + Supported by ``paddr`` operations set. + - ``migrate_cold``: Migrate the regions prioritizing colder regions. + Supported by ``paddr`` operations set. + - ``stat``: Do nothing but count the statistics. + Supported by all operations sets. + +Applying the actions except ``stat`` to a region is considered as changing the +region's characteristics. Hence, DAMOS resets the age of regions when any such +actions are applied to those. + +To know how user-space can set the action via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:`action <sysfs_scheme>` part of the +documentation. .. _damon_design_damos_access_pattern: @@ -311,6 +479,10 @@ interest by setting minimum and maximum values of the three properties. If a region's three properties are in the ranges, DAMOS classifies it as one of the regions that the scheme is having an interest in. +To know how user-space can set the access pattern via :ref:`DAMON sysfs +interface <sysfs_interface>`, refer to :ref:`access_pattern +<sysfs_access_pattern>` part of the documentation. + .. _damon_design_damos_quotas: @@ -330,6 +502,10 @@ feature called quotas. It lets users specify an upper limit of time that DAMOS can use for applying the action, and/or a maximum bytes of memory regions that the action can be applied within a user-specified time duration. +To know how user-space can set the basic quotas via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:`quotas <sysfs_quotas>` part of the +documentation. + .. _damon_design_damos_quotas_prioritization: @@ -357,6 +533,10 @@ information to the underlying mechanism. Nevertheless, how and even whether the weight will be respected are up to the underlying prioritization mechanism implementation. +To know how user-space can set the prioritization weights via :ref:`DAMON sysfs +interface <sysfs_interface>`, refer to :ref:`weights <sysfs_quotas>` part of +the documentation. + .. _damon_design_damos_quotas_auto_tuning: @@ -364,12 +544,37 @@ Aim-oriented Feedback-driven Auto-tuning ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Automatic feedback-driven quota tuning. Instead of setting the absolute quota -value, users can repeatedly provide numbers representing how much of their goal -for the scheme is achieved as feedback. DAMOS then automatically tunes the +value, users can specify the metric of their interest, and what target value +they want the metric value to be. DAMOS then automatically tunes the aggressiveness (the quota) of the corresponding scheme. For example, if DAMOS is under achieving the goal, DAMOS automatically increases the quota. If DAMOS is over achieving the goal, it decreases the quota. +The goal can be specified with four parameters, namely ``target_metric``, +``target_value``, ``current_value`` and ``nid``. The auto-tuning mechanism +tries to make ``current_value`` of ``target_metric`` be same to +``target_value``. + +- ``user_input``: User-provided value. Users could use any metric that they + has interest in for the value. Use space main workload's latency or + throughput, system metrics like free memory ratio or memory pressure stall + time (PSI) could be examples. Note that users should explicitly set + ``current_value`` on their own in this case. In other words, users should + repeatedly provide the feedback. +- ``some_mem_psi_us``: System-wide ``some`` memory pressure stall information + in microseconds that measured from last quota reset to next quota reset. + DAMOS does the measurement on its own, so only ``target_value`` need to be + set by users at the initial time. In other words, DAMOS does self-feedback. +- ``node_mem_used_bp``: Specific NUMA node's used memory ratio in bp (1/10,000). +- ``node_mem_free_bp``: Specific NUMA node's free memory ratio in bp (1/10,000). + +``nid`` is optionally required for only ``node_mem_used_bp`` and +``node_mem_free_bp`` to point the specific NUMA node. + +To know how user-space can set the tuning goal metric, the target value, and/or +the current value via :ref:`DAMON sysfs interface <sysfs_interface>`, refer to +:ref:`quota goals <sysfs_schemes_quota_goals>` part of the documentation. + .. _damon_design_damos_watermarks: @@ -392,6 +597,10 @@ is activated. If all schemes are deactivated by the watermarks, the monitoring is also deactivated. In this case, the DAMON worker thread only periodically checks the watermarks and therefore incurs nearly zero overhead. +To know how user-space can set the watermarks via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:`watermarks <sysfs_watermarks>` part of the +documentation. + .. _damon_design_damos_filters: @@ -407,29 +616,121 @@ have a list of latency-critical processes. To let users optimize DAMOS schemes with such special knowledge, DAMOS provides a feature called DAMOS filters. The feature allows users to set an arbitrary -number of filters for each scheme. Each filter specifies the type of target -memory, and whether it should exclude the memory of the type (filter-out), or -all except the memory of the type (filter-in). - -Currently, anonymous page, memory cgroup, address range, and DAMON monitoring -target type filters are supported by the feature. Some filter target types -require additional arguments. The memory cgroup filter type asks users to -specify the file path of the memory cgroup for the filter. The address range -type asks the start and end addresses of the range. The DAMON monitoring -target type asks the index of the target from the context's monitoring targets -list. Hence, users can apply specific schemes to only anonymous pages, -non-anonymous pages, pages of specific cgroups, all pages excluding those of -specific cgroups, pages in specific address range, pages in specific DAMON -monitoring targets, and any combination of those. - -To handle filters efficiently, the address range and DAMON monitoring target -type filters are handled by the core layer, while others are handled by -operations set. If a memory region is filtered by a core layer-handled filter, -it is not counted as the scheme has tried to the region. In contrast, if a -memory regions is filtered by an operations set layer-handled filter, it is -counted as the scheme has tried. The difference in accounting leads to changes -in the statistics. +number of filters for each scheme. Each filter specifies + +- a type of memory (``type``), +- whether it is for the memory of the type or all except the type + (``matching``), and +- whether it is to allow (include) or reject (exclude) applying + the scheme's action to the memory (``allow``). + +For efficient handling of filters, some types of filters are handled by the +core layer, while others are handled by operations set. In the latter case, +hence, support of the filter types depends on the DAMON operations set. In +case of the core layer-handled filters, the memory regions that excluded by the +filter are not counted as the scheme has tried to the region. In contrast, if +a memory regions is filtered by an operations set layer-handled filter, it is +counted as the scheme has tried. This difference affects the statistics. + +When multiple filters are installed, the group of filters that handled by the +core layer are evaluated first. After that, the group of filters that handled +by the operations layer are evaluated. Filters in each of the groups are +evaluated in the installed order. If a part of memory is matched to one of the +filter, next filters are ignored. If the part passes through the filters +evaluation stage because it is not matched to any of the filters, applying the +scheme's action to it depends on the last filter's allowance type. If the last +filter was for allowing, the part of memory will be rejected, and vice versa. + +For example, let's assume 1) a filter for allowing anonymous pages and 2) +another filter for rejecting young pages are installed in the order. If a page +of a region that eligible to apply the scheme's action is an anonymous page, +the scheme's action will be applied to the page regardless of whether it is +young or not, since it matches with the first allow-filter. If the page is +not anonymous but young, the scheme's action will not be applied, since the +second reject-filter blocks it. If the page is neither anonymous nor young, +the page will pass through the filters evaluation stage since there is no +matching filter, and the action will be applied to the page. + +Below ``type`` of filters are currently supported. + +- Core layer handled + - addr + - Applied to pages that belonging to a given address range. + - target + - Applied to pages that belonging to a given DAMON monitoring target. +- Operations layer handled, supported by only ``paddr`` operations set. + - anon + - Applied to pages that containing data that not stored in files. + - active + - Applied to active pages. + - memcg + - Applied to pages that belonging to a given cgroup. + - young + - Applied to pages that are accessed after the last access check from the + scheme. + - hugepage_size + - Applied to pages that managed in a given size range. + - unmapped + - Applied to pages that unmapped. + +To know how user-space can set the filters via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:`filters <sysfs_filters>` part of the +documentation. + +.. _damon_design_damos_stat: + +Statistics +~~~~~~~~~~ +The statistics of DAMOS behaviors that designed to help monitoring, tuning and +debugging of DAMOS. + +DAMOS accounts below statistics for each scheme, from the beginning of the +scheme's execution. + +- ``nr_tried``: Total number of regions that the scheme is tried to be applied. +- ``sz_trtied``: Total size of regions that the scheme is tried to be applied. +- ``sz_ops_filter_passed``: Total bytes that passed operations set + layer-handled DAMOS filters. +- ``nr_applied``: Total number of regions that the scheme is applied. +- ``sz_applied``: Total size of regions that the scheme is applied. +- ``qt_exceeds``: Total number of times the quota of the scheme has exceeded. + +"A scheme is tried to be applied to a region" means DAMOS core logic determined +the region is eligible to apply the scheme's :ref:`action +<damon_design_damos_action>`. The :ref:`access pattern +<damon_design_damos_access_pattern>`, :ref:`quotas +<damon_design_damos_quotas>`, :ref:`watermarks +<damon_design_damos_watermarks>`, and :ref:`filters +<damon_design_damos_filters>` that handled on core logic could affect this. +The core logic will only ask the underlying :ref:`operation set +<damon_operations_set>` to do apply the action to the region, so whether the +action is really applied or not is unclear. That's why it is called "tried". + +"A scheme is applied to a region" means the :ref:`operation set +<damon_operations_set>` has applied the action to at least a part of the +region. The :ref:`filters <damon_design_damos_filters>` that handled by the +operation set, and the types of the :ref:`action <damon_design_damos_action>` +and the pages of the region can affect this. For example, if a filter is set +to exclude anonymous pages and the region has only anonymous pages, or if the +action is ``pageout`` while all pages of the region are unreclaimable, applying +the action to the region will fail. + +To know how user-space can read the stats via :ref:`DAMON sysfs interface +<sysfs_interface>`, refer to :ref:s`stats <sysfs_stats>` part of the +documentation. + +Regions Walking +~~~~~~~~~~~~~~~ + +DAMOS feature allowing users access each region that a DAMOS action has just +applied. Using this feature, DAMON :ref:`API <damon_design_api>` allows users +access full properties of the regions including the access monitoring results +and amount of the region's internal memory that passed the DAMOS filters. +:ref:`DAMON sysfs interface <sysfs_interface>` also allows users read the data +via special :ref:`files <sysfs_schemes_tried_regions>`. + +.. _damon_design_api: Application Programming Interface --------------------------------- @@ -443,6 +744,8 @@ interface, namely ``include/linux/damon.h``. Please refer to the API :doc:`document </mm/damon/api>` for details of the interface. +.. _damon_modules: + Modules ======= @@ -462,25 +765,22 @@ General Purpose User Interface Modules DAMON modules that provide user space ABIs for general purpose DAMON usage in runtime. -DAMON user interface modules, namely 'DAMON sysfs interface' and 'DAMON debugfs -interface' are DAMON API user kernel modules that provide ABIs to the -user-space. Please note that DAMON debugfs interface is currently deprecated. - -Like many other ABIs, the modules create files on sysfs and debugfs, allow -users to specify their requests to and get the answers from DAMON by writing to -and reading from the files. As a response to such I/O, DAMON user interface -modules control DAMON and retrieve the results as user requested via the DAMON -API, and return the results to the user-space. +Like many other ABIs, the modules create files on pseudo file systems like +'sysfs', allow users to specify their requests to and get the answers from +DAMON by writing to and reading from the files. As a response to such I/O, +DAMON user interface modules control DAMON and retrieve the results as user +requested via the DAMON API, and return the results to the user-space. The ABIs are designed to be used for user space applications development, rather than human beings' fingers. Human users are recommended to use such user space tools. One such Python-written user space tool is available at -Github (https://github.com/awslabs/damo), Pypi +Github (https://github.com/damonitor/damo), Pypi (https://pypistats.org/packages/damo), and Fedora (https://packages.fedoraproject.org/pkgs/python-damo/damo/). -Please refer to the ABI :doc:`document </admin-guide/mm/damon/usage>` for -details of the interfaces. +Currently, one module for this type, namely 'DAMON sysfs interface' is +available. Please refer to the ABI :ref:`doc <sysfs_interface>` for details of +the interfaces. Special-Purpose Access-aware Kernel Modules @@ -488,8 +788,8 @@ Special-Purpose Access-aware Kernel Modules DAMON modules that provide user space ABI for specific purpose DAMON usage. -DAMON sysfs/debugfs user interfaces are for full control of all DAMON features -in runtime. For each special-purpose system-wide data access-aware system +DAMON user interface modules are for full control of all DAMON features in +runtime. For each special-purpose system-wide data access-aware system operations such as proactive reclamation or LRU lists balancing, the interfaces could be simplified by removing unnecessary knobs for the specific purpose, and extended for boot-time and even compile time control. Default values of DAMON |