Comment 38 for bug 543617

I can report that the proposed kernel resolves what is either this issue or a closely related
issue. On our Ubuntu 10.04 machines, unmounting an NFS filesystem takes a significant
amount of time, on the order of several seconds to tens of seconds; my test machine runs
between 15 seconds and 25 seconds per filesystem. This happens even with a 'sync' run
immediately before the unmount.

(This happens on both 2.6.32-24-generic-pae i686 and 2.6.32-24-server x86_64. One
unpleasant consequence is that shutting down a machine takes a very long time, as we
have more than 200 NFS mounts and the shutdown scripts do the unmounts serially.)

The proposed kernel solves the problem on at least x86_64; unmounting a NFS
filesystem is almost instant (time says 0.16 seconds real) and the machine shuts
down or reboots immediately when requested.