exportfs -f question

I have a server which exports 20-30 local filesystems, each with a different fsid=<decimal-ip-address> option. eth0 on the server has one additional ip address for every export. Apart from NLM issues mentioned earlier on this list, what is the best way to drop caches to be able to umount one exported mount-point on the server?

Right now I do a

ip addr del... (remove ip address to block traffic for this export) exportfs -f
umount /exported-mountpoint

but since exportfs -f does a

	time(NULL)                              = 1179165584
	open("/proc/net/rpc/auth.unix.ip/flush", O_RDWR) = 3
	write(3, "1179165584\n", 11)            = 11
	close(3)                                = 0
	open("/proc/net/rpc/nfsd.export/flush", O_RDWR) = 3
	write(3, "1179165584\n", 11)            = 11
	close(3)                                = 0
	open("/proc/net/rpc/nfsd.fh/flush", O_RDWR) = 3
	write(3, "1179165584\n", 11)            = 11
	close(3)                                = 0

I wonder if:

- can above umount fail due to a race with in-kernel operations?
- is there a more efficient way to flush cached filehandles
for a specific export or fsid?
(I have no clue about performance penalty for the other exports)

Frank

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