[issue1872] nfs stall (fix pushed)

[Matthew Dillon]

:I reduced vfs.nfs.maxasyncbio to 16 (from default of 64),
:and haven't seen the 'Insufficient sendspace' since.
:
:NFS stall can still be experienced, if I do 'too many' things at once,
:e.g. doing `git status' with repo and checkout on NFS mounts while
:doing `make -j3 buildworld' did stall NFS.
:
:Forced core dump avail. on request.
:
:Using x86_64 system also still stall NFS (above was i386);
:here forced core dump didn't work out, `panic' failed to generate core dump.

    Are you always getting the 'NFS: Insufficient sendspace' message
    when a stall occurs or do stalls occur sometimes without the
    message?

    The Insufficient sendspace message can only occur with UDP.  What
    happens if you use a TCP NFS mount?  Are you able to stall the mount
    with a TCP NFS mount?

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>