Running BSD from RAM memory using zroot

[Mark Johnston]

On Sun, Aug 23, 2020 at 12:26:07PM -0600, Ian Lepore wrote:
> Note that deleting md0 will not necessarily
> make the memory it was using available for further use.  The memory
> will be in the form of a preloaded module, and it's not clear to me
> that it can be unloaded (but I'm also not sure that it can't be).

On i386 and amd64 preloaded memory can be freed, see
kmem_bootstrap_free().  On other platforms it is leaked.  It is not too
hard to fix for a given platform, the pmap needs to ensure that pages
containing preloaded data and the page table pages mapping preloaded
data are initialized properly.  See r336505 for an example.