tcp: Allocate t_tcpreq_info on demand

When TCP_REQUEST_TRK is enabled, the tcb grows by 600 bytes
to accommodate the t_tcpreq_info[MAX_TCP_TRK_REQ] array.
Even when the option is enabled, not every connection is using
this feature.  So let's allocate it on-demand, and save 600
bytes in the common case.

Sponsored by: Netflix
Reviewed by: rrs, tuexen
Differential Revision: https://reviews.freebsd.org/D56484

sys/netinet/tcp_subr.c

@@ -1133,6 +1133,9 @@ tcp_default_fb_fini(struct tcpcb *tp, int tcb_is_purged)
 
 MALLOC_DEFINE(M_TCPLOG, "tcplog", "TCP address and flags print buffers");
 MALLOC_DEFINE(M_TCPFUNCTIONS, "tcpfunc", "TCP function set memory");
+#ifdef TCP_REQUEST_TRK
+MALLOC_DEFINE(M_TCPREQTRK, "tcpreqtrk", "TCP request tracking");
+#endif
 
 static struct mtx isn_mtx;
 
@@ -2445,6 +2448,12 @@ tcp_discardcb(struct tcpcb *tp)
 #ifdef STATS
 	stats_blob_destroy(tp->t_stats);
 #endif
+#ifdef TCP_REQUEST_TRK
+	if (tp->t_tcpreq_info != NULL) {
+		free(tp->t_tcpreq_info, M_TCPREQTRK);
+		tp->t_tcpreq_info = NULL;
+	}
+#endif
 
 	CC_ALGO(tp) = NULL;
 	if ((m = STAILQ_FIRST(&tp->t_inqueue)) != NULL) {
@@ -4890,6 +4899,14 @@ tcp_req_alloc_req_full(struct tcpcb *tp, struct tcp_snd_req *req, uint64_t ts, i
 	struct tcp_sendfile_track *fil;
 	int i, allocated;
 
+	/* Allocate the request tracking array on demand */
+	if (tp->t_tcpreq_info == NULL) {
+		tp->t_tcpreq_info = malloc(
+		    sizeof(*tp->t_tcpreq_info) * MAX_TCP_TRK_REQ,
+		    M_TCPREQTRK, M_NOWAIT | M_ZERO);
+		if (tp->t_tcpreq_info == NULL)
+			return (NULL);
+	}
 	/* In case the stack does not check for completions do so now */
 	tcp_req_check_for_comp(tp, tp->snd_una);
 	/* Check for stale entries */

sys/netinet/tcp_var.h

@@ -493,7 +493,7 @@ struct tcpcb {
 	uint32_t tcp_hybrid_start;	/* Num of times we started hybrid pacing */
 	uint32_t tcp_hybrid_stop;	/* Num of times we stopped hybrid pacing */
 	uint32_t tcp_hybrid_error;	/* Num of times we failed to start hybrid pacing */
-	struct tcp_sendfile_track t_tcpreq_info[MAX_TCP_TRK_REQ];
+	struct tcp_sendfile_track *t_tcpreq_info;
 #endif
 #ifdef TCP_ACCOUNTING
 	uint64_t tcp_cnt_counters[TCP_NUM_CNT_COUNTERS];