Index: sys/netinet/tcp_hostcache.c
===================================================================
--- sys/netinet/tcp_hostcache.c
+++ sys/netinet/tcp_hostcache.c
@@ -121,6 +121,7 @@
 static struct hc_metrics *tcp_hc_lookup(struct in_conninfo *);
 static struct hc_metrics *tcp_hc_insert(struct in_conninfo *);
 static int sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS);
+static int sysctl_tcp_hc_histo(SYSCTL_HANDLER_ARGS);
 static int sysctl_tcp_hc_purgenow(SYSCTL_HANDLER_ARGS);
 static void tcp_hc_purge_internal(int);
 static void tcp_hc_purge(void *);
@@ -168,6 +169,11 @@
     0, 0, sysctl_tcp_hc_list, "A",
     "List of all hostcache entries");
 
+SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, histo,
+    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_SKIP | CTLFLAG_MPSAFE,
+    0, 0, sysctl_tcp_hc_histo, "A",
+    "Print a histogram of hostcache hashbucket utilization");
+
 SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, purgenow,
     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
     NULL, 0, sysctl_tcp_hc_purgenow, "I",
@@ -692,6 +698,72 @@
 	return(error);
 }
 
+/*
+ * Sysctl function: prints a histogram of the hostcache hashbucket
+ * utilization.
+ */
+static int
+sysctl_tcp_hc_histo(SYSCTL_HANDLER_ARGS)
+{
+	const int linesize = 128;
+	struct sbuf sb;
+	int i, error, n;
+	int *histo_cnt, *histo_tailq;
+	int hch_length;
+	struct hc_metrics *hc_entry;
+
+	if (jailed_without_vnet(curthread->td_ucred) != 0)
+		return (EPERM);
+
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0) {
+		return(error);
+	}
+
+	histo_cnt = (int *)malloc(sizeof(int) * V_tcp_hostcache.bucket_limit, M_TEMP, M_NOWAIT|M_ZERO);
+	if (histo_cnt == NULL) {
+		return(ENOMEM);
+	}
+	histo_tailq = (int *)malloc(sizeof(int) * V_tcp_hostcache.bucket_limit, M_TEMP, M_NOWAIT|M_ZERO);
+	if (histo_tailq == NULL) {
+		return(ENOMEM);
+	}
+
+	/* Use a buffer for 16 lines */
+	sbuf_new_for_sysctl(&sb, NULL, 16 * linesize, req);
+
+	for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
+		hch_length = V_tcp_hostcache.hashbase[i].hch_length;
+		if (hch_length < V_tcp_hostcache.bucket_limit) {
+			histo_cnt[hch_length]++;
+		} else {
+			sbuf_printf(&sb, "excessive bucket length at %u: %u\n", 
+			    i, hch_length);
+		}
+		n = 0;
+		THC_LOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
+		TAILQ_FOREACH(hc_entry, &V_tcp_hostcache.hashbase[i].hch_bucket,
+			      rmx_q) {
+			n++;
+		}
+		THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
+		if (n < V_tcp_hostcache.bucket_limit) {
+			histo_tailq[n]++;
+		} else {
+			sbuf_printf(&sb, "excessive bucket length at %u: %u\n", 
+			    i, n);
+		}
+	}
+
+	sbuf_printf(&sb, "\nLength\tCount\tList\n");
+	for (i = 0; i < V_tcp_hostcache.bucket_limit; i++) {
+		sbuf_printf(&sb, "%u\t%u\t%u\n", i, histo_cnt[i], histo_tailq[i]);
+	}
+	error = sbuf_finish(&sb);
+	sbuf_delete(&sb);
+	return(error);
+}
+
 /*
  * Caller has to make sure the curvnet is set properly.
  */
@@ -714,8 +786,19 @@
 			} else
 				hc_entry->rmx_expire -= V_tcp_hostcache.prune;
 		}
+		if (all)
+			V_tcp_hostcache.hashbase[i].hch_length = 0;
 		THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
 	}
+	if (all && V_tcp_hostcache.cache_count != 0) {
+		for (i = 0; i < V_tcp_hostcache.hashsize; i++)
+			THC_LOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
+		V_tcp_hostcache.cache_count = 0;
+		for (--i; i >= 0 ; i--)
+			V_tcp_hostcache.cache_count += V_tcp_hostcache.hashbase[i].hch_length;
+		for (++i; i < V_tcp_hostcache.hashsize; i++)
+			THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
+	}
 }
 
 /*