Docs/admin-guide/mm/damon/usage: document effective_bytes file

Update DAMON usage document for the effective quota file of the DAMON
sysfs interface.

Link: https://lkml.kernel.org/r/20240219194431.159606-6-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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

@@ -83,7 +83,7 @@ comma (",").
     │ │ │ │ │ │ │ │ sz/min,max
     │ │ │ │ │ │ │ │ nr_accesses/min,max
     │ │ │ │ │ │ │ │ age/min,max
-    │ │ │ │ │ │ │ :ref:`quotas <sysfs_quotas>`/ms,bytes,reset_interval_ms
+    │ │ │ │ │ │ │ :ref:`quotas <sysfs_quotas>`/ms,bytes,reset_interval_ms,effective_bytes
     │ │ │ │ │ │ │ │ weights/sz_permil,nr_accesses_permil,age_permil
     │ │ │ │ │ │ │ │ :ref:`goals <sysfs_schemes_quota_goals>`/nr_goals
     │ │ │ │ │ │ │ │ │ 0/target_value,current_value
@@ -153,6 +153,9 @@ Users can write below commands for the kdamond to the ``state`` file.
 - ``clear_schemes_tried_regions``: Clear the DAMON-based operating scheme
   action tried regions directory for each DAMON-based operation scheme of the
   kdamond.
+- ``update_schemes_effective_bytes``: Update the contents of
+  ``effective_bytes`` files for each DAMON-based operation scheme of the
+  kdamond.  For more details, refer to :ref:`quotas directory <sysfs_quotas>`.
 
 If the state is ``on``, reading ``pid`` shows the pid of the kdamond thread.
 
@@ -320,8 +323,9 @@ schemes/<N>/quotas/
 The directory for the :ref:`quotas <damon_design_damos_quotas>` of the given
 DAMON-based operation scheme.
 
-Under ``quotas`` directory, three files (``ms``, ``bytes``,
-``reset_interval_ms``) and two directores (``weights`` and ``goals``) exist.
+Under ``quotas`` directory, four files (``ms``, ``bytes``,
+``reset_interval_ms``, ``effective_bytes``) and two directores (``weights`` and
+``goals``) exist.
 
 You can set the ``time quota`` in milliseconds, ``size quota`` in bytes, and
 ``reset interval`` in milliseconds by writing the values to the three files,
@@ -332,6 +336,15 @@ apply the action to only up to ``bytes`` bytes of memory regions within the
 quota limits unless at least one :ref:`goal <sysfs_schemes_quota_goals>` is
 set.
 
+The time quota is internally transformed to a size quota.  Between the
+transformed size quota and user-specified size quota, smaller one is applied.
+Based on the user-specified :ref:`goal <sysfs_schemes_quota_goals>`, the
+effective size quota is further adjusted.  Reading ``effective_bytes`` returns
+the current effective size quota.  The file is not updated in real time, so
+users should ask DAMON sysfs interface to update the content of the file for
+the stats by writing a special keyword, ``update_schemes_effective_bytes`` to
+the relevant ``kdamonds/<N>/state`` file.
+
 Under ``weights`` directory, three files (``sz_permil``,
 ``nr_accesses_permil``, and ``age_permil``) exist.
 You can set the :ref:`prioritization weights