- Cache the vm page in the PVO instead of looking it up on every action.
- Search pmap's ESID tree lockless
VSIDs are only created, never destroyed, during a process's lifetime.
Rather than hold the PMAP lock for the entire duration of lookup and
create-if-needed, only take the lock if the first lookup fails, and
release as necessary.
Cache the vm page in the PVO instead of looking it up on every action
Usually we have the page already on PVO insert, so keep that around to
avoid calling PHYS_TO_VM_PAGE(), which could be costly.