[RFC v2 5/9] Docs/damon: Document 'initial_regions' feature

[SeongJae Park <sjpark@amazon.com>]

From: SeongJae Park <sjpark@amazon.de>

This commit documents the 'initial_regions' feature.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
 Documentation/admin-guide/mm/damon/usage.rst | 34 ++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index 18a19c35b4f3..137ed770c2d6 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -326,6 +326,40 @@ having pids 42 and 4242 as the processes to be monitored and check it again::
 Note that setting the pids doesn't start the monitoring.
 
 
+Initla Monitoring Target Regions
+--------------------------------
+
+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.::
+
+    <pid> <start address> <end address>
+
+The ``pid`` should be already in ``pids`` 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.  DAMON will
+automatically updates the boundary of the regions after one ``regions update
+interval``.  Therefore, users should set the ``regions update interval`` large
+enough.
+
+
 Record
 ------
 
-- 
2.17.1