Throughput problems with NFS

[David Rhodus]

I have been able to duplicate the problems Richard Sharpe was
having while using Linux as a client. This seems to have a limiting
factor of throttling the throughput to around 5MB/s.  This is caused
from the segment remaining un-acked so adding a reserve of 2048
bytes will work around for this. I've added a sysctl to allow finer 
grain
control over this option.

You can obtain the patch from:
http://machdep.com/drhodus/nfs_sack.diff
-DR