[RFC PATCH 1/5] mm/damon/core: introduce damos_quota_goal_tuner

[SeongJae Park <sj@kernel.org>]

Currently DAMOS quota goal feature utilizes a single feedback loop based
algorithm for automatic tuning of the effective quota.  It is proven to
be useful on dynamic environments that operate systems with only
kernels.  But, no one fits all, and we got multiple reports [1,2] of
cases that the algorithm is not optimum.

Introduce a new field of 'struct damos_quotas', namely 'goal_tuner'.  It
specifies what tuning algorithm the given scheme should use, and allows
DAMON API callers to set it as they want.  Nonetheless, this commit does
not introduce a new tuning algorithm but only the interface.  This
commit hence makes no behavioral change.  A new algorithm will be added
by the following commit.

[1] https://lore.kernel.org/CALa+Y17__d=ZsM1yX+MXx0ozVdsXnFqF4p0g+kATEitrWyZFfg@mail.gmail.com
[2] https://lore.kernel.org/20260204022537.814-1-yunjeong.mun@sk.com

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 9 +++++++++
 mm/damon/core.c       | 4 +++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index a4fea23da8576..25345b5f821b9 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -213,6 +213,14 @@ struct damos_quota_goal {
 	struct list_head list;
 };
 
+/**
+ * enum damos_quota_goal_tuner - Goal-based quota tuning logic.
+ * @DAMOS_QUOTA_GOAL_TUNER_CONSIST:	Aim long term consistent quota.
+ */
+enum damos_quota_goal_tuner {
+	DAMOS_QUOTA_GOAL_TUNER_CONSIST,
+};
+
 /**
  * struct damos_quota - Controls the aggressiveness of the given scheme.
  * @reset_interval:	Charge reset interval in milliseconds.
@@ -260,6 +268,7 @@ struct damos_quota {
 	unsigned long ms;
 	unsigned long sz;
 	struct list_head goals;
+	enum damos_quota_goal_tuner goal_tuner;
 	unsigned long esz;
 
 	unsigned int weight_sz;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 0ff190ed8a599..1c126d910fe62 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -405,8 +405,9 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 	INIT_LIST_HEAD(&scheme->list);
 
 	scheme->quota = *(damos_quota_init(quota));
-	/* quota.goals should be separately set by caller */
+	/* quota.goals and .goal_tuner should be separately set by caller */
 	INIT_LIST_HEAD(&scheme->quota.goals);
+	scheme->quota.goal_tuner = DAMOS_QUOTA_GOAL_TUNER_CONSIST;
 
 	scheme->wmarks = *wmarks;
 	scheme->wmarks.activated = true;
@@ -860,6 +861,7 @@ static int damos_commit_quota(struct damos_quota *dst, struct damos_quota *src)
 	err = damos_commit_quota_goals(dst, src);
 	if (err)
 		return err;
+	dst->goal_tuner = src->goal_tuner;
 	dst->weight_sz = src->weight_sz;
 	dst->weight_nr_accesses = src->weight_nr_accesses;
 	dst->weight_age = src->weight_age;
-- 
2.47.3