Docs/admin-guide/mm/damon/usage: clarify quotas and watermarks sysfs interface

Explanation of DAMOS quotas and watermarks are not clearly explaining the
meaning and expectation of each file.  Add more clarification for those.

Link: https://lkml.kernel.org/r/20230616191742.87531-7-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>

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index ea6a5dc..9d3ebd7 100644 (file)
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -306,7 +306,8 @@ Under the ``access_pattern`` directory, three directories (``sz``,
 ``nr_accesses``, and ``age``) each having two files (``min`` and ``max``)
 exist.  You can set and get the access pattern for the given scheme by writing
 to and reading from the ``min`` and ``max`` files under ``sz``,
-``nr_accesses``, and ``age`` directories, respectively.
+``nr_accesses``, and ``age`` directories, respectively.  Note that the ``min``
+and the ``max`` form a closed interval.
 
 schemes/<N>/quotas/
 -------------------
@@ -320,7 +321,13 @@ Under ``quotas`` directory, three files (``ms``, ``bytes``,
 
 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,
-respectively.  You can also set the :ref:`prioritization weights
+respectively.  Then, DAMON tries to use only up to ``time quota`` milliseconds
+for applying the ``action`` to memory regions of the ``access_pattern``, and to
+apply the action to only up to ``bytes`` bytes of memory regions within the
+``reset_interval_ms``.  Setting both ``ms`` and ``bytes`` zero disables the
+quota limits.
+
+You can also set the :ref:`prioritization weights
 <damon_design_damos_quotas_prioritization>` for size, access frequency, and age
 in per-thousand unit by writing the values to the three files under the
 ``weights`` directory.