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Docs/mm/damon/design: add a section for the modules layer 

Add a section for covering DAMON modules layer to the design document.

Link: https://lkml.kernel.org/r/20230525214314.5204-11-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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SeongJae Park 2023-05-25 21:43:14 +00:00 committed by Andrew Morton
parent f508a0fbd3
commit da9698105c
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Documentation/mm/damon/design.rst
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@ -370,3 +370,64 @@ access-aware applications using DAMON's core features. For this, DAMON exposes
its all features to other kernel components via its application programming
interface, namely ``include/linux/damon.h``. Please refer to the API
:doc:`document </mm/damon/api>` for details of the interface.
Modules
=======
Because the core of DAMON is a framework for kernel components, it doesn't
provide any direct interface for the user space. Such interfaces should be
implemented by each DAMON API user kernel components, instead. DAMON subsystem
itself implements such DAMON API user modules, which are supposed to be used
for general purpose DAMON control and special purpose data access-aware system
operations, and provides stable application binary interfaces (ABI) for the
user space. The user space can build their efficient data access-aware
applications using the interfaces.
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.
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
(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.
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
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
control parameters for the usage would also need to be optimized for the
purpose.
To support such cases, yet more DAMON API user kernel modules that provide more
simple and optimized user space interfaces are available. Currently, two
modules for proactive reclamation and LRU lists manipulation are provided. For
more detail, please read the usage documents for those
(:doc:`/admin-guide/mm/damon/reclaim` and
:doc:`/admin-guide/mm/damon/lru_sort`).