[patch 229/262] Docs/admin-guide/mm/damon: document DAMON-based Operation Schemes

Andrew Morton
2021-11-05T20:46:42Z

From: SeongJae Park <sj@kernel.org>
Subject: Docs/admin-guide/mm/damon: document DAMON-based Operation Schemes

This commit add description of DAMON-based operation schemes in the DAMON
documents.

Link: https://lkml.kernel.org/r/20211001125604.29660-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Amit Shah <amit@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rienjes <rientjes@google.com>
Cc: David Woodhouse <dwmw@amazon.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Leonard Foerster <foersleo@amazon.de>
Cc: Marco Elver <elver@google.com>
Cc: Markus Boehme <markubo@amazon.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

Documentation/admin-guide/mm/damon/start.rst | 11 +++
Documentation/admin-guide/mm/damon/usage.rst | 51 ++++++++++++++++-
2 files changed, 60 insertions(+), 2 deletions(-)

--- a/Documentation/admin-guide/mm/damon/start.rst~docs-admin-guide-mm-damon-document-damon-based-operation-schemes
+++ a/Documentation/admin-guide/mm/damon/start.rst
@@ -108,6 +108,17 @@ the results as separate image files. ::
You can view the visualizations of this example workload at [1]_.
Visualizations of other realistic workloads are available at [2]_ [3]_ [4]_.

+
+Data Access Pattern Aware Memory Management
+===========================================
+
+Below three commands make every memory region of size >=4K that doesn't
+accessed for >=60 seconds in your workload to be swapped out. ::
+
+ $ echo "#min-size max-size min-acc max-acc min-age max-age action" > scheme
+ $ echo "4K max 0 0 60s max pageout" >> scheme
+ $ damo schemes -c my_thp_scheme <pid of your workload>
+
.. [1] https://damonitor.github.io/doc/html/v17/admin-guide/mm/damon/start.html#visualizing-recorded-patterns
.. [2] https://damonitor.github.io/test/result/visual/latest/rec.heatmap.1.png.html
.. [3] https://damonitor.github.io/test/result/visual/latest/rec.wss_sz.png.html
--- a/Documentation/admin-guide/mm/damon/usage.rst~docs-admin-guide-mm-damon-document-damon-based-operation-schemes
+++ a/Documentation/admin-guide/mm/damon/usage.rst
@@ -34,8 +34,8 @@ the reason, this document describes only
debugfs Interface
=================

-DAMON exports three files, ``attrs``, ``target_ids``, and ``monitor_on`` under
-its debugfs directory, ``<debugfs>/damon/``.
+DAMON exports four files, ``attrs``, ``target_ids``, ``schemes`` and
+``monitor_on`` under its debugfs directory, ``<debugfs>/damon/``.

Attributes
@@ -74,6 +74,53 @@ check it again::
Note that setting the target ids doesn't start the monitoring.

+Schemes
+-------
+
+For usual DAMON-based data access aware memory management optimizations, users
+would simply want the system to apply a memory management action to a memory
+region of a specific size having a specific access frequency for a specific
+time. DAMON receives such formalized operation schemes from the user and
+applies those to the target processes. It also counts the total number and
+size of regions that each scheme is applied. This statistics can be used for
+online analysis or tuning of the schemes.
+
+Users can get and set the schemes by reading from and writing to ``schemes``
+debugfs file. Reading the file also shows the statistics of each scheme. To
+the file, each of the schemes should be represented in each line in below form:
+
+ min-size max-size min-acc max-acc min-age max-age action
+
+Note that the ranges are closed interval. Bytes for the size of regions
+(``min-size`` and ``max-size``), number of monitored accesses per aggregate
+interval for access frequency (``min-acc`` and ``max-acc``), number of
+aggregate intervals for the age of regions (``min-age`` and ``max-age``), and a
+predefined integer for memory management actions should be used. The supported
+numbers and their meanings are as below.
+
+ - 0: Call ``madvise()`` for the region with ``MADV_WILLNEED``
+ - 1: Call ``madvise()`` for the region with ``MADV_COLD``
+ - 2: Call ``madvise()`` for the region with ``MADV_PAGEOUT``
+ - 3: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``
+ - 4: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``
+ - 5: Do nothing but count the statistics
+
+You can disable schemes by simply writing an empty string to the file. For
+example, below commands applies a scheme saying "If a memory region of size in
+[4KiB, 8KiB] is showing accesses per aggregate interval in [0, 5] for aggregate
+interval in [10, 20], page out the region", check the entered scheme again, and
+finally remove the scheme. ::
+
+ # cd <debugfs>/damon
+ # echo "4096 8192 0 5 10 20 2" > schemes
+ # cat schemes
+ 4096 8192 0 5 10 20 2 0 0
+ # echo > schemes
+
+The last two integers in the 4th line of above example is the total number and
+the total size of the regions that the scheme is applied.
+
+
Turning On/Off
--------------

_