// 150 already in use (MSG_OSD_RECOVERY_RESERVE)
-#define MSG_MDS_RESOLVE 0x200
+#define MSG_MDS_RESOLVE 0x200 // 0x2xx are for mdcache of mds
#define MSG_MDS_RESOLVEACK 0x201
#define MSG_MDS_CACHEREJOIN 0x202
#define MSG_MDS_DISCOVER 0x203
#define MSG_MDS_OPENINOREPLY 0x210
#define MSG_MDS_SNAPUPDATE 0x211
#define MSG_MDS_FRAGMENTNOTIFYACK 0x212
-#define MSG_MDS_LOCK 0x300
+#define MSG_MDS_LOCK 0x300 // 0x3xx are for locker of mds
#define MSG_MDS_INODEFILECAPS 0x301
-#define MSG_MDS_METRICS 0x302
-#define MSG_MDS_PING 0x303
-#define MSG_MDS_EXPORTDIRDISCOVER 0x449
+#define MSG_MDS_EXPORTDIRDISCOVER 0x449 // 0x4xx are for migrator of mds
#define MSG_MDS_EXPORTDIRDISCOVERACK 0x450
#define MSG_MDS_EXPORTDIRCANCEL 0x451
#define MSG_MDS_EXPORTDIRPREP 0x452
#define MSG_MDS_GATHERCAPS 0x472
#define MSG_MDS_HEARTBEAT 0x500 // for mds load balancer
+#define MSG_MDS_METRICS 0x501 // for mds metric aggregator
+#define MSG_MDS_PING 0x502 // for mds pinger
// *** generic ***
#define MSG_TIMECHECK 0x600