This is some work on VM locking in order to address some lock contention
issues seen on large machines. This is an initial port to current sources
and separation of the patches from the others needed to run on the machines.

Perhaps it is valuable to be able to see my steps retraced, as the initial
writing of the patches is preserved and in turn bugfixes as I implemented
them are introduced in separate patches.

Applies against 2.4.19-pre5-ac3
(1) reverse mapping VM due to Rik van Riel
(2) radix tree pagecache due to Momchil Velikov and Christoph Hellwig
(3) finegrained LRU list locking originally due to Arjan van de Ven
(4) finegrained pte_chain locking originally due to Martin Bligh

-- wli
Mon Apr  8 17:51:49 PDT 2002