About netstat -m: What is "mbuf+clusters out of packet secondary zone in use" ?

[Yony Yossef]

Hi All,
 
I'm testing an Ethernet driver on FreeBSD 6.3.
 
Running netstat -m during an ethernt stress test I see that the
"mbuf+clusters out of packet secondary zone in use" number is growing
gradualy.
Problem is it never goes down after I stop the test, so it's pushing the
"mbufs in use" up until the following stress test iterations reach the OS
limit.
What does this number mean? 
 
 
506391/126009/632400 mbufs in use (current/cache/total)
141035/121109/262144/262144 mbuf clusters in use (current/cache/total/max)
131054/610 mbuf+clusters out of packet secondary zone in use (current/cache)
 
 
Thanks
Yony