Add a variant of DAMOS_QUOTA_NODE_MEMCG_USED_BP, for the free memory
portion.  The value of the metric is implemented as the entire memory of
the given NUMA node subtracted by the given cgroup's usage.  So from a
perspective, "unused" could be a better term than "free".  But arguably
it is not very clear what is better, so use the term "free".

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 6 ++++--
 mm/damon/core.c       | 9 +++++++--
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 0d63ceb7e6ef..0edf41d36ea1 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -148,6 +148,7 @@ enum damos_action {
  * @DAMOS_QUOTA_NODE_MEM_USED_BP:	MemUsed ratio of a node.
  * @DAMOS_QUOTA_NODE_MEM_FREE_BP:	MemFree ratio of a node.
  * @DAMOS_QUOTA_NODE_MEMCG_USED_BP:	MemUsed ratio of a node for a cgroup.
+ * @DAMOS_QUOTA_NODE_MEMCG_FREE_BP:	MemFree ratio of a node for a cgroup.
  * @NR_DAMOS_QUOTA_GOAL_METRICS:	Number of DAMOS quota goal metrics.
  *
  * Metrics equal to larger than @NR_DAMOS_QUOTA_GOAL_METRICS are unsupported.
@@ -158,6 +159,7 @@ enum damos_quota_goal_metric {
 	DAMOS_QUOTA_NODE_MEM_USED_BP,
 	DAMOS_QUOTA_NODE_MEM_FREE_BP,
 	DAMOS_QUOTA_NODE_MEMCG_USED_BP,
+	DAMOS_QUOTA_NODE_MEMCG_FREE_BP,
 	NR_DAMOS_QUOTA_GOAL_METRICS,
 };
 
@@ -183,8 +185,8 @@ enum damos_quota_goal_metric {
  * If @metric is DAMOS_QUOTA_NODE_MEM_{USED,FREE}_BP, @nid represents the node
  * id of the target node to account the used/free memory.
  *
- * If @metric is DAMOS_QUOTA_NODE_MEMCG_USED_BP, @nid and @memcg_id represents
- * the node id and the cgroup to account the used memory for.
+ * If @metric is DAMOS_QUOTA_NODE_MEMCG_{USED,FREE}_BP, @nid and @memcg_id
+ * represents the node id and the cgroup to account the used memory for.
  */
 struct damos_quota_goal {
 	enum damos_quota_goal_metric metric;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 1eacf78aa358..a31ede50906c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2039,7 +2039,7 @@ static unsigned long damos_get_node_memcg_used_bp(
 {
 	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
-	unsigned long used_pages;
+	unsigned long used_pages, numerator;
 	struct sysinfo i;
 
 	rcu_read_lock();
@@ -2059,7 +2059,11 @@ static unsigned long damos_get_node_memcg_used_bp(
 	used_pages += lruvec_page_state(lruvec, NR_INACTIVE_FILE);
 
 	si_meminfo_node(&i, goal->nid);
-	return used_pages * 10000 / i.totalram;
+	if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP)
+		numerator = used_pages;
+	else	/* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */
+		numerator = i.totalram - used_pages;
+	return numerator * 10000 / i.totalram;
 }
 #else
 static __kernel_ulong_t damos_get_node_mem_bp(
@@ -2094,6 +2098,7 @@ static void damos_set_quota_goal_current_value(struct damos_quota_goal *goal)
 		goal->current_value = damos_get_node_mem_bp(goal);
 		break;
 	case DAMOS_QUOTA_NODE_MEMCG_USED_BP:
+	case DAMOS_QUOTA_NODE_MEMCG_FREE_BP:
 		goal->current_value = damos_get_node_memcg_used_bp(goal);
 		break;
 	default:
-- 
2.39.5