mm/damon/design.rst

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
23 DAMON subsystem is configured with three layers including
25 - Operations Set: Implements fundamental operations for DAMON that depends on
26   the given monitoring target address-space and available set of
28 - Core: Implements core logics including monitoring overhead/accurach control
29   and access-aware system operations on top of the operations set layer, and
30 - Modules: Implements kernel modules for various purposes that provides
34 Configurable Operations Set
35 ---------------------------
41 space.  DAMON separates the two parts in different layers, namely DAMON
42 Operations Set and DAMON Core Logics Layers, respectively.  It further defines
43 the interface between the layers to allow various operations sets to be
53 check primitives, those will be easily configurable.
57 --------------------
78 VMA-based Target Address Range Construction
79 -------------------------------------------
85 Only small parts in the super-huge virtual address space of the processes are
97 heap and the uppermost mmap()-ed region, and the gap between the lowermost
98 mmap()-ed region and the stack in most of the cases.  Because these gaps are
100 to make a reasonable trade-off.  Below shows this in detail::
104     <uppermost mmap()-ed region>
105     (small mmap()-ed regions and munmap()-ed regions)
106     <lowermost mmap()-ed region>
111 PTE Accessed-bit Based Access Check
112 -----------------------------------
115 Accessed-bit for basic access checks.  Only one difference is the way of
134 ----------
152 clears the results.  This can be described in below simple pseudo-code::
183 minimum and the maximum number of regions for the trade-off.
202 will not exceed the user-specified maximum number of regions after the split.
204 In this way, DAMON provides its best-effort quality and minimal overhead while
205 keeping the bounds users set for their trade-off.
229 be hot-plugged.
233 and applies it to monitoring operations-related data structures such as the
234 abstracted monitoring target memory area only for each of a user-specified time
241 -----------------
243 One common purpose of data access monitoring is access-aware system efficiency
253 One straightforward approach for such schemes would be profile-guided
270 works, DAMON provides a feature called Data Access Monitoring-based Operation
273 the access pattern of interest, and applies the user-desired operation actions
274 to the regions, for every user-specified time interval called
320 DAMOS upper-bound overhead control feature.  DAMOS could incur high overhead if
328 To mitigate that situation, DAMOS provides an upper-bound overhead control
331 the action can be applied within a user-specified time duration.
345 rarely accessed (colder) memory regions would be prioritized for page-out
363 Aim-oriented Feedback-driven Auto-tuning
366 Automatic feedback-driven quota tuning.  Instead of setting the absolute quota
401 Non-access pattern-based target memory regions filtering.  If users run
402 self-written programs or have good profiling tools, they could know something
406 have a list of latency-critical processes.
411 memory, and whether it should exclude the memory of the type (filter-out), or
412 all except the memory of the type (filter-in).
421 non-anonymous pages, pages of specific cgroups, all pages excluding those of
427 operations set.  If a memory region is filtered by a core layer-handled filter,
429 memory regions is filtered by an operations set layer-handled filter, it is
435 ---------------------------------
437 The programming interface for kernel space data access-aware applications.
440 access-aware applications using DAMON's core features.  For this, DAMON exposes
453 for general purpose DAMON control and special purpose data access-aware system
455 user space.  The user space can build their efficient data access-aware
460 --------------------------------------
467 user-space.  Please note that DAMON debugfs interface is currently deprecated.
473 API, and return the results to the user-space.
477 user space tools.  One such Python-written user space tool is available at
480 (https://packages.fedoraproject.org/pkgs/python-damo/damo/).
482 Please refer to the ABI :doc:`document </admin-guide/mm/damon/usage>` for
486 Special-Purpose Access-aware Kernel Modules
487 -------------------------------------------
492 in runtime.  For each special-purpose system-wide data access-aware system
495 extended for boot-time and even compile time control.  Default values of DAMON
503 (:doc:`/admin-guide/mm/damon/reclaim` and
504 :doc:`/admin-guide/mm/damon/lru_sort`).