diff --git a/dm/syncer/compactor.go b/dm/syncer/compactor.go
index 217fd2e7626..f4ef7627020 100644
--- a/dm/syncer/compactor.go
+++ b/dm/syncer/compactor.go
@@ -39,6 +39,8 @@ type compactor struct {
 
 // compactorWrap creates and runs a compactor instance.
 func compactorWrap(inCh chan *job, syncer *Syncer) chan *job {
+	// Actually we can use a larger compact buffer-size, but if so, when user pause-task/stop-task, they may need to wait a longer time to wait all jobs flushed.
+	// TODO: implement ping-pong buffer.
 	bufferSize := syncer.cfg.QueueSize * syncer.cfg.WorkerCount / 4
 	compactor := &compactor{
 		inCh:       inCh,
diff --git a/dm/syncer/syncer.go b/dm/syncer/syncer.go
index 44dce10c748..4327c8c82d4 100644
--- a/dm/syncer/syncer.go
+++ b/dm/syncer/syncer.go
@@ -268,6 +268,9 @@ func NewSyncer(cfg *config.SubTaskConfig, etcdClient *clientv3.Client, notifier
 
 func (s *Syncer) newJobChans() {
 	s.closeJobChans()
+	// DM originally cached s.cfg.QueueSize * s.cfg.WorkerCount dml jobs in memory in 2.0.X.
+	// Now if compact: false, dmlJobCh and dmlWorker will both cached s.cfg.QueueSize * s.cfg.WorkerCount/2 jobs. 
+	// If compact: true, dmlJobCh, compactor buffer, compactor output channel and dmlWorker will all cached s.cfg.QueueSize * s.cfg.WorkerCount/4 jobs.
 	chanSize := s.cfg.QueueSize * s.cfg.WorkerCount / 2
 	if s.cfg.Compact {
 		chanSize /= 2