Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -3435,7 +3435,13 @@
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
 	TCPSTAT_INC(tcps_rttupdated);
-	tp->t_rttupdated++;
+	if (tp->t_rttupdated < UTYPE_MAX(tp->t_rttupdated)) {
+		/*
+		 * track updates to RTT in tcpcb only the initial few
+		 * rounds explicitly, to save space in tcpcb
+		 */
+		tp->t_rttupdated++;
+	}
 	if ((tp->t_srtt != 0) && (tp->t_rxtshift <= TCP_RTT_INVALIDATE)) {
 		/*
 		 * srtt is stored as fixed point with 5 bits after the
Index: sys/netinet/tcp_stacks/rack.c
===================================================================
--- sys/netinet/tcp_stacks/rack.c
+++ sys/netinet/tcp_stacks/rack.c
@@ -3680,7 +3680,13 @@
 	}
 	TCPSTAT_INC(tcps_rttupdated);
 	rack_log_rtt_upd(tp, rack, rtt, o_srtt, o_var);
-	tp->t_rttupdated++;
+	if (tp->t_rttupdated < UTYPE_MAX(tp->t_rttupdated)) {
+		/*
+		 * track updates to RTT in tcpcb only the initial few
+		 * rounds explicitly, to save space in tcpcb
+		 */
+		tp->t_rttupdated++;
+	}
 #ifdef NETFLIX_STATS
 	stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RTT, imax(0, rtt));
 #endif
Index: sys/netinet/tcp_usrreq.c
===================================================================
--- sys/netinet/tcp_usrreq.c
+++ sys/netinet/tcp_usrreq.c
@@ -2622,7 +2622,7 @@
 	    tp->t_rttbest);
 
 	db_print_indent(indent);
-	db_printf("t_rttupdated: %lu   max_sndwnd: %u   t_softerror: %d\n",
+	db_printf("t_rttupdated: %u   max_sndwnd: %u   t_softerror: %d\n",
 	    tp->t_rttupdated, tp->max_sndwnd, tp->t_softerror);
 
 	db_print_indent(indent);
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -178,9 +178,9 @@
 	uint32_t  snd_cwnd_prev;	/* cwnd prior to retransmit */
 	uint32_t  snd_ssthresh_prev;	/* ssthresh prior to retransmit */
 	tcp_seq	snd_recover_prev;	/* snd_recover prior to retransmit */
-	int	t_sndzerowin;		/* zero-window updates sent */
-	u_long	t_rttupdated;		/* number of times rtt sampled */
-	int	snd_numholes;		/* number of holes seen by sender */
+	uint32_t  t_sndzerowin;		/* zero-window updates sent (per-flow-stats only) */
+	uint8_t	  t_rttupdated;		/* number of times rtt sampled */
+	int32_t	  snd_numholes;		/* number of holes seen by sender */
 	u_int	t_badrxtwin;		/* window for retransmit recovery */
 	TAILQ_HEAD(sackhole_head, sackhole) snd_holes;
 					/* SACK scoreboard (sorted) */
@@ -192,18 +192,18 @@
 	int	t_rttlow;		/* smallest observerved RTT */
 	int	rfbuf_cnt;		/* recv buffer autoscaling byte count */
 	struct toedev	*tod;		/* toedev handling this connection */
-	int	t_sndrexmitpack;	/* retransmit packets sent */
-	int	t_rcvoopack;		/* out-of-order packets received */
+	uint32_t  t_sndrexmitpack;	/* retransmit packets sent (per-flow-stats only) */
+	uint32_t  t_rcvoopack;		/* out-of-order packets received (per-flow-stats only) */
 	void	*t_toe;			/* TOE pcb pointer */
 	struct cc_algo	*cc_algo;	/* congestion control algorithm */
 	struct cc_var	*ccv;		/* congestion control specific vars */
 	struct osd	*osd;		/* storage for Khelp module data */
-	int	t_bytes_acked;		/* # bytes acked during current RTT */
-	u_int   t_maxunacktime;
-	u_int	t_keepinit;		/* time to establish connection */
-	u_int	t_keepidle;		/* time before keepalive probes begin */
-	u_int	t_keepintvl;		/* interval between keepalives */
-	u_int	t_keepcnt;		/* number of keepalives before close */
+	uint32_t  t_bytes_acked;	/* # bytes acked during current RTT */
+	uint32_t  t_maxunacktime;
+	uint32_t  t_keepinit;		/* time to establish connection */
+	uint32_t  t_keepidle;		/* time before keepalive probes begin */
+	uint32_t  t_keepintvl;		/* interval between keepalives */
+	uint32_t  t_keepcnt;		/* number of keepalives before close */
 	int	t_dupacks;		/* consecutive dup acks recd */
 	int	t_lognum;		/* Number of log entries */
 	struct tcp_log_stailq t_logs;	/* Log buffer */
@@ -495,6 +495,14 @@
 	max((tp)->t_rttmin, (((tp)->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT))  \
 	  + (tp)->t_rttvar) >> TCP_DELTA_SHIFT)
 
+/*
+ * programmatically determine the maximum value of
+ * a signed or unsigned type, without integer overflow
+ */
+#define	UTYPE_MAX(x) \
+	((((1 << (sizeof(x)*8 - 1)) - 1) * 2) + 1)
+#define TYPE_MAX(x) \
+	((((1 << (sizeof(x)*8 - 2)) - 1) * 2) + 1)
 /*
  * TCP statistics.
  * Many of these should be kept per connection,
@@ -696,9 +704,9 @@
 	int64_t		spare64[8];
 	int32_t		t_state;		/* (s,p) */
 	uint32_t	t_flags;		/* (s,p) */
-	int32_t		t_sndzerowin;		/* (s) */
-	int32_t		t_sndrexmitpack;	/* (s) */
-	int32_t		t_rcvoopack;		/* (s) */
+	uint32_t	t_sndzerowin;		/* (s) */
+	uint32_t	t_sndrexmitpack;	/* (s) */
+	uint32_t	t_rcvoopack;		/* (s) */
 	int32_t		t_rcvtime;		/* (s) */
 	int32_t		tt_rexmt;		/* (s) */
 	int32_t		tt_persist;		/* (s) */