Add a knob to allow reclaim of the directory vnodes that are source of the namecache records. The reclamation is not enabled by default because for typical workload it would make namecache unusable, but large nested directory tree easily puts any process that accesses filesystem into 1 second wait for vlru.
Add a knob to allow reclaim of the directory vnodes that are source of
the namecache records. The reclamation is not enabled by default because
for typical workload it would make namecache unusable, but large nested
directory tree easily puts any process that accesses filesystem into 1
second wait for vlru.

Reported by:	yar (long time ago)
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase