bitkeeper revision 1.1385.1.6 (426fa4d8AQ8dQHrihxXpPojuqYnL0g)

bitkeeper revision 1.1385.1.6 (426fa4d8AQ8dQHrihxXpPojuqYnL0g)

Improve multi-processor XenLinux fork/exec/destroy times. We do this
by lazily pinning page-tables for p.t. use, and aggressively unpinning
them on last use, to put as little pressure on the batched wrpt
interface as possible. Basically this means that the copy loop and
destroy loop will usually be able to directly write pagetables with no
Xen intervention at all (implicit or explicit).
Signed-off-by: Keir Fraser <keir@xensource.com>