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

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

[Liew Rui Yan]

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

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

[SJ Park]

On Thu, 10 Sep 2026 19:22:31 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> 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.

Thank you for this patch.

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

Reviewed-by: SJ Park <sj@kernel.org>

This patch is applied to damon/next [1] tree.  If this patch is not added to
mm.git in short term (~1 week?), I will ask mm.git maintainer (Andrew Morton)
to pick this.  So, no action from your side is needed for now.  If it seems I
also forgot doing that or you cannot wait for my action, please feel free to
directly ask that to Andrew.

[1] https://origin.kernel.org/doc/html/latest/mm/damon/maintainer-profile.html#scm-trees


Thanks,
SJ

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