damos_quota_goal kerneldoc comment is not explaining when @metric is
used.  Update the comment for that.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index cae8c613c5fc..dc9c310e0e75 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -176,6 +176,9 @@ enum damos_quota_goal_metric {
  * If @metric is DAMOS_QUOTA_USER_INPUT, @current_value should be manually
  * entered by the user, probably inside the kdamond callbacks.  Otherwise,
  * DAMON sets @current_value with self-measured value of @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.
  */
 struct damos_quota_goal {
 	enum damos_quota_goal_metric metric;
-- 
2.39.5