address-space is a non-recursive data structure, which contains a flat list of vm_areas representing
mapped vm-objects.
userspace programs can no longer create sub-address-spaces. instead, they can reserve portions of
the address space, and use that reserved space to create mappings.
the rules around acquiring locks have been strictly defined and
implemented, and general lock usage has been improved, to fix and
prevent several different issues.
a vm-region is now destroyed in two separate steps:
1. it is "killed": all mappings are unmapped and deleted, the
region is removed from its parent, and the region and all of
its sub-regions are marked as "dead", preventing any
further actions from being performed with the region.
2. it is "destroyed": the vm-region object is de-allocated when
the last reference/handle is closed. the references that this
region holds to any sub-regions are also released, meaning
these regions may also be de-allocated too.
