Doing DAMOS_LRU_[DE]PRIO with DAMOS_QUOTA_[IN]ACTIVE_MEM_BP based quota
auto-tuning can be useful.  For example, users can ask DAMON to "find
hot/cold pages and activate/deactivate those aiming 50:50
active:inactive memory size."  But DAMON_LRU_SORT has no interface to do
that.  Add a module parameter for setting the target ratio.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/lru_sort.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
index 3ccde23a8566..99c5a22cf3f2 100644
--- a/mm/damon/lru_sort.c
+++ b/mm/damon/lru_sort.c
@@ -41,6 +41,20 @@ static bool enabled __read_mostly;
 static bool commit_inputs __read_mostly;
 module_param(commit_inputs, bool, 0600);
 
+/*
+ * Desired active to [in]active memory ratio in bp (1/10,000).
+ *
+ * While keeping the caps that set by other quotas, DAMON_LRU_SORT
+ * automatically increases and decreases the effective level of the quota
+ * aiming the LRU [de]prioritizations of the hot and cold memory resulting in
+ * this active to [in]active memory ratio.  Value zero means disabling this
+ * auto-tuning feature.
+ *
+ * Disabled by default.
+ */
+static unsigned long active_mem_bp __read_mostly;
+module_param(active_mem_bp, ulong, 0600);
+
 /*
  * Filter [none-]young pages accordingly for LRU [de]prioritizations.
  *
@@ -201,6 +215,26 @@ static struct damos *damon_lru_sort_new_cold_scheme(unsigned int cold_thres)
 	return damon_lru_sort_new_scheme(&pattern, DAMOS_LRU_DEPRIO);
 }
 
+static int damon_lru_sort_add_quota_goals(struct damos *hot_scheme,
+		struct damos *cold_scheme)
+{
+	struct damos_quota_goal *goal;
+
+	if (!active_mem_bp)
+		return 0;
+	goal = damos_new_quota_goal(DAMOS_QUOTA_ACTIVE_MEM_BP, active_mem_bp);
+	if (!goal)
+		return -ENOMEM;
+	damos_add_quota_goal(&hot_scheme->quota, goal);
+	/* aim 0.2 % goal conflict, to keep little ping pong */
+	goal = damos_new_quota_goal(DAMOS_QUOTA_INACTIVE_MEM_BP,
+			10000 - active_mem_bp + 2);
+	if (!goal)
+		return -ENOMEM;
+	damos_add_quota_goal(&hot_scheme->quota, goal);
+	return 0;
+}
+
 static int damon_lru_sort_add_filters(struct damos *hot_scheme,
 		struct damos *cold_scheme)
 {
@@ -256,6 +290,9 @@ static int damon_lru_sort_apply_parameters(void)
 	damon_set_schemes(param_ctx, &hot_scheme, 1);
 	damon_add_scheme(param_ctx, cold_scheme);
 
+	err = damon_lru_sort_add_quota_goals(hot_scheme, cold_scheme);
+	if (err)
+		goto out;
 	err = damon_lru_sort_add_filters(hot_scheme, cold_scheme);
 	if (err)
 		goto out;
-- 
2.39.5