knfsd: Remove NLM_HOST_MAX and associated logic.

knfsd: Remove NLM_HOST_MAX and associated logic.

Lockd caches information about hosts that have recently held locks to
expedite the taking of further locks.

It periodically discards this information for hosts that have not been
used for a few minutes.

lockd currently has a value NLM_HOST_MAX, and changes the 'garbage
collection' behaviour when the number of hosts exceeds this threshold.

However its behaviour is strange, and likely not what was intended.
When the number of hosts exceeds the max, it scans *less* often (every
2 minutes vs every minute) and allows unused host information to
remain around longer (5 minutes instead of 2).

Having this limit is of dubious value anyway, and we have not
suffered from the code not getting the limit right, so remove the
limit altogether.  We go with the larger values (discard 5 minute old
hosts every 2 minutes) as they are probably safer.

Maybe the periodic garbage collection should be replace to with
'shrinker' handler so we just respond to memory pressure....

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>