mm/damon/design.rst

32   overhead/accuracy control and access-aware system operations on top of the
46 For data access monitoring and additional low level work, DAMON needs a set of
48 the given target address space.  For example, below two operations for access
52 2. Access check of specific address range in the target space.
67 Also, if some architectures or devices support special optimized access check
121 PTE Accessed-bit Based Access Check
125 Accessed-bit for basic access checks.  Only one difference is the way of
159 Access Frequency Monitoring
163 duration.  The resolution of the access frequency is controlled by setting
165 access to each page per ``sampling interval`` and aggregates the results.  In
192 that assumed to have the same access frequencies into a region.  As long as the
193 assumption (pages in a region have the same access frequencies) is kept, only
197 increases the access frequency counter of the region if so.  The counter is
210 fulfill the assumption (pages in same region have similar access frequencies),
211 the data access pattern can be dynamically changed.  This will result in low
213 adaptively merges and splits each region based on their access frequency.
215 For each ``aggregation interval``, it compares the access frequencies
220 regions``, it repeats the merging with increasing access frequenceis difference
224 aggregated access frequency of each region, it splits each region into two or
238 access pattern of a region has maintained.  That could be used for good
239 understanding of the access pattern.  For example, page placement algorithm
241 To make such access pattern maintained period analysis easier, DAMON maintains
243 interval``, DAMON checks if the region's size and access frequency
272 One common purpose of data access monitoring is access-aware system efficiency
280     access frequency for more than one minute.
283 optimizations.  That is, getting data access monitoring results of the
299 works, DAMON provides a feature called Data Access Monitoring-based Operation
302 the access pattern of interest, and applies the user-desired operation actions
365 Target Access Pattern
368 The access pattern of the schemes' interest.  The patterns are constructed with
370 the access frequency, and the age.  Users can describe their access pattern of
375 To know how user-space can set the access pattern via :ref:`DAMON sysfs
386 the target access pattern is not properly tuned.  For example, if a huge memory
387 region having the access pattern of interest is found, applying the scheme's
389 resources.  Preventing such issues by tuning the access pattern could be
390 challenging, especially if the access patterns of the workloads are highly
420 to calculate the priority using the access pattern properties of the regions.
423 (``age``) more than the access frequency (``nr_accesses``).  DAMOS allows users
424 to specify the weight of each access pattern property and passes the
498 Non-access pattern-based target memory regions filtering.  If users run
500 more than the kernel, such as future access patterns or some special
528     - Applied to pages that are accessed after the last access check from the
546 The programming interface for kernel space data access-aware applications.
549 access-aware applications using DAMON's core features.  For this, DAMON exposes
564 for general purpose DAMON control and special purpose data access-aware system
566 user space.  The user space can build their efficient data access-aware
597 Special-Purpose Access-aware Kernel Modules
603 in runtime.  For each special-purpose system-wide data access-aware system