[RFC PATCH 15/17] Docs/mm/damon/design: document probe preps

[SJ Park]

Update DAMON design document for the newly added DAMN probe preps
feature.

Signed-off-by: SJ Park <sj@xxxxxxxxxx>
---
 Documentation/mm/damon/design.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index 12a2c3f81a262..5ce777c6b3f30 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -311,6 +311,13 @@ Users can therefore know how much of a given DAMON region has a specific data
 attribute by reading the per-region per-probe probe hits counter after each
 aggregation interval.
 
+Users can optionally register probing preparation actions per probe.  If such
+actions are registered, DAMON applies the actions to each region's sampling
+memory before starting the next sampling interval.  Currently only one action,
+``set_pgidle`` is supported.  The action marks the page for the probing target
+memory as access-idle.  This can be useful to be used together with
+``pgidle_unset`` probe filter.
+
 This is a sampling based mechanism.  Hence, it is lightweight but the output
 may include some measurement errors.  The output should be used with good
 understanding of statistics.
-- 
2.47.3