"nfsd server cache flooded"

[Ryan Stone]

Earlier in the week I tried running a buildworld on a 11.1-RELEASE
system that had /usr/obj mounted via nfsv4 from a 12-CURRENT server.
After some time, the build hung I saw this message start repeating in
/var/log/messages:

May 15 08:23:03 rstone-server kernel: nfsd server cache flooded, try
increasing vfs.nfsd.tcphighwater

In 12-CURRENT, sysctl vfs.nfsd.tcphighwater defaults to 0, so I have
no idea what a reasonable value to set would be.  Any advice?