Advisory pageout, task map fragmentation, and other stuff

[Sergio Lopez]

Hi,

I've described some of the work I've done the past months on the wiki:

 - http://www.bddebian.com/~hurd-web/user/Sergio_Lopez/

I also plan to publish a working version of memfs (a tmpfs variant
which replaces the default pager with a pool of anonymous memory) in
the next few days.