vnlru proc is extremely inefficient, potentially iteration over tens of
thousands of vnodes without blocking. Droping Giant allows other threads
to preempt us although we should revisit the algorithm to fix the runtime
problems especially since this may hold up all vnode allocations.
- Remove the LK_NOWAIT from the VOP_LOCK in vlrureclaim. This provides
a natural blocking point to help alleviate the situation described above
although it may not technically be desirable.
- yield after we make a pass on all mount points to prevent us from
blocking other threads which require Giant.
MFC after: 2 weeks
39b2406838