[RFC v2 9/9] Docs/damon: Document physical memory monitoring support

[SeongJae Park <sjpark@amazon.com>]

From: SeongJae Park <sjpark@amazon.de>

This commit adds description for the physical memory monitoring usage in
the DAMON document.

Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
 Documentation/admin-guide/mm/damon/usage.rst | 42 ++++++++++++++------
 1 file changed, 29 insertions(+), 13 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index 137ed770c2d6..359745f0dbfb 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -314,27 +314,42 @@ check it again::
 Target PIDs
 -----------
 
-Users can get and set the pids of monitoring target processes by reading from
-and writing to the ``pids`` file.  For example, below commands set processes
-having pids 42 and 4242 as the processes to be monitored and check it again::
+To monitor the virtual memory address spaces of specific processes, users can
+get and set the pids of monitoring target processes by reading from and writing
+to the ``pids`` file.  For example, below commands set processes having pids 42
+and 4242 as the processes to be monitored and check it again::
 
     # cd <debugfs>/damon
     # echo 42 4242 > pids
     # cat pids
     42 4242
 
+Users can also monitor the physical memory address space of the system by
+writing a special keyword, "``paddr\n``" to the file.  In this case, reading the
+file will show ``-1``, as below::
+
+    # cd <debugfs>/damon
+    # echo paddr > pids
+    # cat pids
+    -1
+
 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 case of the virtual memory 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 contrast, DAMON do not automatically sets and updates the monitoring target
+regions in case of physical memory monitoring.  Therefore, users should set the
+monitoring target regions by themselves.
 
 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
@@ -354,10 +369,11 @@ region of process 42, and another couple of address ranges, ``20-40`` and
             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.
+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