[$] Further progress toward removing the page map count

The mapcount field was created to track the number of mappings(page-table entries) that refer to the given page. Among other things, amapcount of zero means that the page has no references and can bereclaimed. Maintaining mapcount has become increasinglychallenging and expensive as the memory-management system has grown incomplexity, so Hildenbrand has been looking for ways to get rid of it.This session was, he said, maybe one of the last times he will have tobring up this topic.