[RFC v7 05/10] Docs/admin-guide/mm/damon: Document 'init_regions' feature

[SeongJae Park <sjpark@amazon.com>]

From: SeongJae Park <sjpark@amazon.de>

This commit adds description of the 'init_regions' feature in the DAMON
usage document.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
 Documentation/admin-guide/mm/damon/usage.rst | 41 +++++++++++++++++++-
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index 96278227f925..cf0d44ce0ac9 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -281,8 +281,9 @@ for at least 100 milliseconds using below commands::
 debugfs Interface
 =================
 
-DAMON exports five files, ``attrs``, ``target_ids``, ``record``, ``schemes``
-and ``monitor_on`` under its debugfs directory, ``<debugfs>/damon/``.
+DAMON exports six files, ``attrs``, ``target_ids``, ``init_regions``,
+``record``, ``schemes`` and ``monitor_on`` under its debugfs directory,
+``<debugfs>/damon/``.
 
 
 Attributes
@@ -321,6 +322,42 @@ check it again::
 Note that setting the target ids doesn't start the monitoring.
 
 
+Initial Monitoring Target Regions
+---------------------------------
+
+In case of the debugfs based monitoring, DAMON automatically sets and updates
+the monitoring target regions so that entire memory mappings of target
+processes can be covered. However, users might want to limit the monitoring
+region to specific address ranges, such as the heap, the stack, or specific
+file-mapped area.  Or, some users might know the initial access pattern of
+their workloads and therefore want to set optimal initial regions for the
+'adaptive regions adjustment'.
+
+In such cases, users can explicitly set the initial monitoring target regions
+as they want, by writing proper values to the ``init_regions`` file.  Each line
+of the input should represent one region in below form.::
+
+    <target id> <start address> <end address>
+
+The ``target id`` should already in ``target_ids`` file, and the regions should
+be passed in address order.  For example, below commands will set a couple of
+address ranges, ``1-100`` and ``100-200`` as the initial monitoring target
+region of process 42, and another couple of address ranges, ``20-40`` and
+``50-100`` as that of process 4242.::
+
+    # cd <debugfs>/damon
+    # echo "42   1       100
+            42   100     200
+            4242 20      40
+            4242 50      100" > init_regions
+
+Note that this sets the initial monitoring target regions only.  In case of
+virtual memory monitoring, DAMON will automatically updates the boundary of the
+regions after one ``regions update interval``.  Therefore, users should set the
+``regions update interval`` large enough in this case, if they don't want the
+update.
+
+
 Record
 ------
 
-- 
2.17.1