Consider required constraint when moving pages from active to inactive lists.

Consider required constraint when moving pages from active to inactive lists.

Make sure low pages are deactivated first when there is a shortage of inactive
pages.  Without this the system can have a ton of high pages on the active list
and never swapout anything if there's a shortage of low pages.

This prevents a deadlock on amd64 reported and tested by bluhm@.

ok kettenis@