Docs/admin-guide/mm/damon/usage: update for {core,ops}_filters directories

Document {core,ops}_filters directories on usage document.

Link: https://lkml.kernel.org/r/20250305222733.59089-9-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>

Author: sjp38

Documentation/admin-guide/mm/damon/usage.rst

@@ -83,7 +83,7 @@ comma (",").
     │ │ │ │ │ │ │ │ :ref:`goals <sysfs_schemes_quota_goals>`/nr_goals
     │ │ │ │ │ │ │ │ │ 0/target_metric,target_value,current_value
     │ │ │ │ │ │ │ :ref:`watermarks <sysfs_watermarks>`/metric,interval_us,high,mid,low
-    │ │ │ │ │ │ │ :ref:`filters <sysfs_filters>`/nr_filters
+    │ │ │ │ │ │ │ :ref:`{core_,ops_,}filters <sysfs_filters>`/nr_filters
     │ │ │ │ │ │ │ │ 0/type,matching,allow,memcg_path,addr_start,addr_end,target_idx,min,max
     │ │ │ │ │ │ │ :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
@@ -307,9 +307,10 @@ to ``N-1``.  Each directory represents each DAMON-based operation scheme.
 schemes/<N>/
 ------------
 
-In each scheme directory, five directories (``access_pattern``, ``quotas``,
-``watermarks``, ``filters``, ``stats``, and ``tried_regions``) and three files
-(``action``, ``target_nid`` and ``apply_interval``) exist.
+In each scheme directory, seven directories (``access_pattern``, ``quotas``,
+``watermarks``, ``core_filters``, ``ops_filters``, ``filters``, ``stats``, and
+``tried_regions``) and three files (``action``, ``target_nid`` and
+``apply_interval``) exist.
 
 The ``action`` file is for setting and getting the scheme's :ref:`action
 <damon_design_damos_action>`.  The keywords that can be written to and read
@@ -420,13 +421,24 @@ The ``interval`` should written in microseconds unit.
 
 .. _sysfs_filters:
 
-schemes/<N>/filters/
---------------------
+schemes/<N>/{core\_,ops\_,}filters/
+-----------------------------------
 
-The directory for the :ref:`filters <damon_design_damos_filters>` of the given
+Directories for :ref:`filters <damon_design_damos_filters>` of the given
 DAMON-based operation scheme.
 
-In the beginning, this directory has only one file, ``nr_filters``.  Writing a
+``core_filters`` and ``ops_filters`` directories are for the filters handled by
+the DAMON core layer and operations set layer, respectively.  ``filters``
+directory can be used for installing filters regardless of their handled
+layers.  Filters that requested by ``core_filters`` and ``ops_filters`` will be
+installed before those of ``filters``.  All three directories have same files.
+
+Use of ``filters`` directory can make expecting evaluation orders of given
+filters with the files under directory bit confusing.  Users are hence
+recommended to use ``core_filters`` and ``ops_filters`` directories.  The
+``filters`` directory could be deprecated in future.
+
+In the beginning, the directory has only one file, ``nr_filters``.  Writing a
 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.
@@ -435,7 +447,7 @@ Each filter directory contains nine files, namely ``type``, ``matching``,
 ``allow``, ``memcg_path``, ``addr_start``, ``addr_end``, ``min``, ``max``
 and ``target_idx``.  To ``type`` file, you can write the type of the filter.
 Refer to :ref:`the design doc <damon_design_damos_filters>` for available type
-names and their meanings.
+names, their meaning and on what layer those are handled.
 
 For ``memcg`` type, you can specify the memory cgroup of the interest by
 writing the path of the memory cgroup from the cgroups mount point to
@@ -455,6 +467,7 @@ the ``type`` and ``matching`` should be allowed or not.
 For example, below restricts a DAMOS action to be applied to only non-anonymous
 pages of all memory cgroups except ``/having_care_already``.::
 
+    # cd ops_filters/0/
     # echo 2 > nr_filters
     # # disallow anonymous pages
     echo anon > 0/type