[PATCH] Docs/mm/damon/design: clarify when qt_exceeds increases

[Liew Rui Yan <aethernet65535@gmail.com>]

qt_exceeds counts how many times a scheme's quota has been exceeded.

When using the temporal auto-tuning algorithm, the effective size quota
becomes zero once the goal is [over-]achieved.  In this case, the quotas
are still set, so qt_exceeds keeps increasing once per quota reset
interval while the goal stays achieved.

Clarify this behavior in the design document.

Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
---

Changes from RFC v1:
- RFC v1: https://lore.kernel.org/damon/20260908175105.42558-2-aethernet65535@gmail.com
- Simplify the explanation.  Do not provide a complete definition of
  qt_exceeds, but rather explain only the increment condition when using
  temporal auto-tuning algorithm, simply to prevent users from becoming
  confused and being unable to find any explanation.

---
 Documentation/mm/damon/design.rst | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index d036340dae8a..3f38a3cf68e4 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -695,7 +695,9 @@ There are two such tuning algorithms that users can select as they need.
   fast as possible, using maximum allowed quota, but only for a temporal short
   time.  When the quota is under-achieved, this algorithm keeps tuning quota to
   a maximum allowed one.  Once the quota is [over]-achieved, this sets the
-  quota zero.  Useful for deterministic control required environments.
+  quota zero.  Useful for deterministic control required environments.  Note
+  that the zero quota is a valid quota, and therefore ``qt_exceeds`` :ref:`stat
+  <damon_design_damos_stat>` will keep increasing in this case.
 
 The goal can be specified with five parameters, namely ``target_metric``,
 ``target_value``, ``current_value``, ``nid`` and ``path``.  The auto-tuning
-- 
2.55.0