to this pmap.c. This new r/w lock is used primarily to synchronize access
to the TTE lists. However, it will be used in a somewhat unconventional
way. As finer-grained TTE list locking is added to each of the pmap
functions that acquire this r/w lock, its acquisition will be changed from
write to read, enabling concurrent execution of the pmap functions with
finer-grained locking.
Reviewed by: attilio
Tested by: flo
MFC after: 10 days
2616fac7a2