[PATCH 10/10] Docs/admin-guide/mm/damon/usage: document DAMOS filter 'pass' sysfs file

SeongJae Park
2025-01-07T20:18:19Z

Update DAMON usage document for the newly added 'pass' sysfs file for
DAMOS filters.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
Documentation/admin-guide/mm/damon/usage.rst | 34 ++++++++++++--------
1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index 8df3357dcfa3..77064c704bf2 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -83,7 +83,7 @@ comma (",").
│ │ │ │ │ │ │ │ │ 0/target_metric,target_value,current_value
│ │ │ │ │ │ │ :ref:`watermarks <sysfs_watermarks>`/metric,interval_us,high,mid,low
│ │ │ │ │ │ │ :ref:`filters <sysfs_filters>`/nr_filters
- │ │ │ │ │ │ │ │ 0/type,matching,memcg_id
+ │ │ │ │ │ │ │ │ 0/type,matching,memcg_id,pass
│ │ │ │ │ │ │ :ref:`stats <sysfs_schemes_stats>`/nr_tried,sz_tried,nr_applied,sz_applied,sz_ops_filter_passed,qt_exceeds
│ │ │ │ │ │ │ :ref:`tried_regions <sysfs_schemes_tried_regions>`/total_bytes
│ │ │ │ │ │ │ │ 0/start,end,nr_accesses,age,sz_filter_passed
@@ -406,13 +406,14 @@ number (``N``) to the file creates the number of child directories named ``0``
to ``N-1``. Each directory represents each filter. The filters are evaluated
in the numeric order.

-Each filter directory contains six files, namely ``type``, ``matcing``,
-``memcg_path``, ``addr_start``, ``addr_end``, and ``target_idx``. To ``type``
-file, you can write one of five special keywords: ``anon`` for anonymous pages,
-``memcg`` for specific memory cgroup, ``young`` for young pages, ``addr`` for
-specific address range (an open-ended interval), or ``target`` for specific
-DAMON monitoring target filtering. Meaning of the types are same to the
-description on the :ref:`design doc <damon_design_damos_filters>`.
+Each filter directory contains seven files, namely ``type``, ``matcing``,
+``pass``, ``memcg_path``, ``addr_start``, ``addr_end``, and ``target_idx``. To
+``type`` file, you can write one of five special keywords: ``anon`` for
+anonymous pages, ``memcg`` for specific memory cgroup, ``young`` for young
+pages, ``addr`` for specific address range (an open-ended interval), or
+``target`` for specific DAMON monitoring target filtering. Meaning of the
+types are same to the description on the :ref:`design doc
+<damon_design_damos_filters>`.

In case of the memory cgroup filtering, you can specify the memory cgroup of
the interest by writing the path of the memory cgroup from the cgroups mount
@@ -422,25 +423,30 @@ specify the start and end address of the range to ``addr_start`` and
you can specify the index of the target between the list of the DAMON context's
monitoring targets list to ``target_idx`` file.

-You can write ``Y`` or ``N`` to ``matching`` file to filter out pages that does
-or does not match to the type, respectively. Then, the scheme's action will
-not be applied to the pages that specified to be filtered out.
+You can write ``Y`` or ``N`` to ``matching`` file to specify whether the filter
+is for memory that matches the ``type``. You can write ``Y`` or ``N`` to
+``pass`` file to specify should this filter let the memory that satisfies the
+``type`` and ``matching`` pass though (allow) or be blocked by (reject) the
+filter. Allowing means the scheme's action will be applied to the memory.

For example, below restricts a DAMOS action to be applied to only non-anonymous
pages of all memory cgroups except ``/having_care_already``.::

# echo 2 > nr_filters
- # # filter out anonymous pages
+ # # block anonymous pages
echo anon > 0/type
echo Y > 0/matching
+ echo N > 0/pass
# # further filter out all cgroups except one at '/having_care_already'
echo memcg > 1/type
echo /having_care_already > 1/memcg_path
echo Y > 1/matching
+ echo N > 1/pass

Refer to the :ref:`DAMOS filters design documentation
-<damon_design_damos_filters>` for more details including when each of the
-filters are supported and differences on stats.
+<damon_design_damos_filters>` for more details including how multiple filters
+of different ``pass`` works, when each of the filters are supported, and
+differences on stats.

.. _sysfs_schemes_stats:

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