Umount nfs strangely slow

[Jonathan Ryshpan]

I am mounting a few filesystems from one F10 machine to another.  Mount
works rapidly but umount of each of the filesystems takes about 20
seconds.  Is this normal?  Could I have the systems misconfigured in any
obvious way?  Both machines have x86_64 processors.

Here is the file /etc/exports on the server machine:
        /                              amito(ro,sync,no_root_squash)
and here is the corresponding mount command on the client machine:
        # mount -t nfs claremont:/        /mnt/claremont
Here is a typical umount command on the client machine:
        # time umount /mnt/claremont/
        real	0m21.029s
        user	0m0.001s
        sys	0m0.004s

Any ideas?  Thanks - jon