linux-kernel - [RFC PATCH 6/8] Docs/mm/damon/design: document for intervals auto-tuning

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Message-Id: <20250213014438.145611-7-sj@kernel.org>
Date: Wed, 12 Feb 2025 17:44:36 -0800
From: SeongJae Park <sj@...nel.org>
To: 
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	damon@...ts.linux.dev,
	kernel-team@...a.com,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [RFC PATCH 6/8] Docs/mm/damon/design: document for intervals auto-tuning

Document DAMON sampling and aggregation intervals auto-tuning design.

Signed-off-by: SeongJae Park <sj@...nel.org>
---
 Documentation/mm/damon/design.rst | 34 +++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index e28c6a1b40ae..c8e906ac3965 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -313,6 +313,10 @@ 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::
@@ -321,6 +325,36 @@ Refer to below documents for an example tuning based on the above guide.
    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 heats to observe with DAMON within given time
+interval.  The target can be specified by the user as a ratio of access check
+samples that gave positive result to the total samples (``samples_bp``) that
+measured within a given number of aggregations (``aggrs``).  The mechanism
+calculates the ratio of access check samples for ``aggrs`` aggregations, and
+increases or decrease the ``sampleing interval`` and ``aggregation interval``
+in same ratio, if the samples 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, 20% access samples ratio target
+is recommended.
+
+
 .. _damon_design_damos:
 
 Operation Schemes
-- 
2.39.5