diff --git a/internal/datacoord/segment_manager.go b/internal/datacoord/segment_manager.go
index fb9cb58332..9671b92ad4 100644
--- a/internal/datacoord/segment_manager.go
+++ b/internal/datacoord/segment_manager.go
@@ -67,15 +67,15 @@ const segmentMaxLifetime = 24 * time.Hour
 
 // Manager manage segment related operations.
 type Manager interface {
-	// AllocSegment allocate rows and record the allocation.
+	// AllocSegment allocates rows and record the allocation.
 	AllocSegment(ctx context.Context, collectionID, partitionID UniqueID, channelName string, requestRows int64) ([]*Allocation, error)
-	// DropSegment drop the segment from allocator.
+	// DropSegment drops the segment from manager.
 	DropSegment(ctx context.Context, segmentID UniqueID)
-	// SealAllSegments sealed all segmetns of collection with collectionID and return sealed segments
+	// SealAllSegments seals all segments of collection with collectionID and return sealed segments
 	SealAllSegments(ctx context.Context, collectionID UniqueID) ([]UniqueID, error)
-	// GetFlushableSegments return flushable segment ids
+	// GetFlushableSegments returns flushable segment ids
 	GetFlushableSegments(ctx context.Context, channel string, ts Timestamp) ([]UniqueID, error)
-	// ExpireAllocations notify segment status to expire old allocations
+	// ExpireAllocations notifies segment status to expire old allocations
 	ExpireAllocations(channel string, ts Timestamp) error
 }
 
@@ -341,7 +341,7 @@ func (s *SegmentManager) estimateMaxNumOfRows(collectionID UniqueID) (int, error
 	return s.estimatePolicy(collMeta.Schema)
 }
 
-// DropSegment puts back all the allocation of provided segment
+// DropSegment drop the segment from manager.
 func (s *SegmentManager) DropSegment(ctx context.Context, segmentID UniqueID) {
 	sp, _ := trace.StartSpanFromContext(ctx)
 	defer sp.Finish()
@@ -356,6 +356,7 @@ func (s *SegmentManager) DropSegment(ctx context.Context, segmentID UniqueID) {
 	segment := s.meta.GetSegment(segmentID)
 	if segment == nil {
 		log.Warn("failed to get segment", zap.Int64("id", segmentID))
+		return
 	}
 	s.meta.SetAllocations(segmentID, []*Allocation{})
 	for _, allocation := range segment.allocations {
@@ -363,7 +364,7 @@ func (s *SegmentManager) DropSegment(ctx context.Context, segmentID UniqueID) {
 	}
 }
 
-// SealAllSegments seals all segments of provided collectionID
+// SealAllSegments seals all segmetns of collection with collectionID and return sealed segments
 func (s *SegmentManager) SealAllSegments(ctx context.Context, collectionID UniqueID) ([]UniqueID, error) {
 	sp, _ := trace.StartSpanFromContext(ctx)
 	defer sp.Finish()