Commit 10418f26 authored by SeongJae Park's avatar SeongJae Park Committed by Andrew Morton
Browse files

Docs/mm/damon/design: add 'statistics' section 

DAMOS stats are important feature for tuning of DAMOS-based access-aware
system operation, and efficient access pattern monitoring.  But not well
documented on the design document.  Add a section on the document.

Link: https://lkml.kernel.org/r/20250106193401.109161-3-sj@kernel.org


Signed-off-by: default avatarSeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 626ffabe

Documentation/mm/damon/design.rst

+38 −0
Original line number Diff line number Diff line
@@ -539,6 +539,44 @@ To know how user-space can set the watermarks via :ref:`DAMON sysfs interface 
<sysfs_interface>`, refer to :ref:`filters <sysfs_filters>` part of the

documentation.



Statistics

~~~~~~~~~~



The statistics of DAMOS behaviors that designed to help monitoring, tuning and

debugging of DAMOS.



DAMOS accounts below statistics for each scheme, from the beginning of the

scheme's execution.



- ``nr_tried``: Total number of regions that the scheme is tried to be applied.

- ``sz_trtied``: Total size of regions that the scheme is tried to be applied.

- ``nr_applied``: Total number of regions that the scheme is applied.

- ``sz_applied``: Total size of regions that the scheme is applied.

- ``qt_exceeds``: Total number of times the quota of the scheme has exceeded.



"A scheme is tried to be applied to a region" means DAMOS core logic determined

the region is eligible to apply the scheme's :ref:`action

<damon_design_damos_action>`.  The :ref:`access pattern

<damon_design_damos_access_pattern>`, :ref:`quotas

<damon_design_damos_quotas>`, :ref:`watermarks

<damon_design_damos_watermarks>`, and :ref:`filters

<damon_design_damos_filters>` that handled on core logic could affect this.

The core logic will only ask the underlying :ref:`operation set

<damon_operations_set>` to do apply the action to the region, so whether the

action is really applied or not is unclear.  That's why it is called "tried".



"A scheme is applied to a region" means the :ref:`operation set

<damon_operations_set>` has applied the action to at least a part of the

region.  The :ref:`filters <damon_design_damos_filters>` that handled by the

operation set, and the types of the :ref:`action <damon_design_damos_action>`

and the pages of the region can affect this.  For example, if a filter is set

to exclude anonymous pages and the region has only anonymous pages, or if the

action is ``pageout`` while all pages of the region are unreclaimable, applying

the action to the region will fail.



To know how user-space can read the stats via :ref:`DAMON sysfs interface

<sysfs_interface>`, refer to :ref:s`stats <sysfs_stats>` part of the

documentation.



Regions Walking

~~~~~~~~~~~~~~~