mpd5/Netgraph issues after upgrading to 7.4

[Przemyslaw Frasunek]

> Use command "vmstat -z|egrep 'ITEM|NetGraph'" and check FAILURES column.
> If you see non-zero values there, you need to increase netgraph memory limits
> net.graph.maxdata and net.graph.maxalloc using /boot/loader.conf.

Unfortunately, increasing net.graph.maxdata & net.graph.maxalloc didn't
solved EPERM problems on netgraph control sockets. It is still appearing
every few hours, but failure counters are zero:

ITEM                     SIZE     LIMIT      USED      FREE  REQUESTS
FAILURES
NetGraph items:            36,    65598,        0,     1404,    52978,
      0
NetGraph data items:       36,    65598,        0,      780,  2876420,
      0

I also tried to increase kern.ipc.nmbclusters to 262140, but after that,
mpd stopped accepting any connections - each failed with ENOBUFS.

What is the upper limit of kernel memory usage?