The patch titled
Subject: Docs/mm/damon/design: add sections for basic parts of DAMOS
has been added to the -mm mm-unstable branch. Its filename is
docs-mm-damon-design-add-sections-for-basic-parts-of-damos.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/docs-mm-damon-design-add-sections-for-basic-parts-of-damos.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: SeongJae Park <sj@xxxxxxxxxx>
Subject: Docs/mm/damon/design: add sections for basic parts of DAMOS
Date: Thu, 25 May 2023 21:43:11 +0000
DAMOS is an important part of DAMON, but the design doc is not covering
it. Add sections for covering the basic part of DAMOS.
Link: https://lkml.kernel.org/r/20230525214314.5204-8-sj@xxxxxxxxxx
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/mm/damon/design.rst | 70 ++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)
--- a/Documentation/mm/damon/design.rst~docs-mm-damon-design-add-sections-for-basic-parts-of-damos
+++ a/Documentation/mm/damon/design.rst
@@ -202,3 +202,73 @@ monitoring operations to check dynamic c
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``).
+
+
+Operation Schemes
+-----------------
+
+One common purpose of data access monitoring is access-aware system efficiency
+optimizations. For example,
+
+ paging out memory regions that are not accessed for more than two minutes
+
+or
+
+ using THP for memory regions that are larger than 2 MiB and showing a high
+ access frequency for more than one minute.
+
+One straightforward approach for such schemes would be profile-guided
+optimizations. That is, getting data access monitoring results of the
+workloads or the system using DAMON, finding memory regions of special
+characteristics by profiling the monitoring results, and making system
+operation changes for the regions. The changes could be made by modifying or
+providing advice to the software (the application and/or the kernel), or
+reconfiguring the hardware. Both offline and online approaches could be
+available.
+
+Among those, providing advice to the kernel at runtime would be flexible and
+effective, and therefore widely be used. However, implementing such schemes
+could impose unnecessary redundancy and inefficiency. The profiling could be
+redundant if the type of interest is common. Exchanging the information
+including monitoring results and operation advice between kernel and user
+spaces could be inefficient.
+
+To allow users to reduce such redundancy and inefficiencies by offloading the
+works, DAMON provides a feature called Data Access Monitoring-based Operation
+Schemes (DAMOS). It lets users specify their desired schemes at a high
+level. For such specifications, DAMON starts monitoring, finds regions having
+the access pattern of interest, and applies the user-desired operation actions
+to the regions as soon as found.
+
+
+Operation Action
+~~~~~~~~~~~~~~~~
+
+The management action that the users desire to apply to the regions of their
+interest. For example, paging out, prioritizing for next reclamation victim
+selection, advising ``khugepaged`` to collapse or split, or doing nothing but
+collecting statistics of the regions.
+
+The list of supported actions is defined in DAMOS, but the implementation of
+each action is in the DAMON operations set layer because the implementation
+normally depends on the monitoring target address space. For example, the code
+for paging specific virtual address ranges out would be different from that for
+physical address ranges. And the monitoring operations implementation sets are
+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.
+
+
+Target Access Pattern
+~~~~~~~~~~~~~~~~~~~~~
+
+The access pattern of the schemes' interest. The patterns are constructed with
+the properties that DAMON's monitoring results provide, specifically the size,
+the access frequency, and the age. Users can describe their access pattern of
+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.
_
Patches currently in -mm which might be from sj@xxxxxxxxxx are
docs-mm-damon-faq-remove-old-questions.patch
docs-mm-damon-maintainer-profile-fix-typos-and-grammar-errors.patch
docs-mm-damon-design-add-a-section-for-overall-architecture.patch
docs-mm-damon-design-update-the-layout-based-on-the-layers.patch
docs-mm-damon-design-rewrite-configurable-layers.patch
docs-mm-damon-design-add-a-section-for-the-relation-between-core-and-modules-layer.patch
docs-mm-damon-design-add-sections-for-basic-parts-of-damos.patch
docs-mm-damon-design-add-sections-for-advanced-features-of-damos.patch
docs-mm-damon-design-add-a-section-for-damon-core-api.patch
docs-mm-damon-design-add-a-section-for-the-modules-layer.patch
