GC configuration docs

[Dan Olson via Digitalmars-d-learn]

I haven't played with any of the new GC configuration options introduced
in 2.067, but now need to.  An application on watchOS currently has
about 30 MB of RAM.  Is there any more documentation than the web page
https://dlang.org/spec/garbage.html or should I just browse druntime
code?

Also pointers (pun maybe) on finding who has the references keeping memory from
being collected.
-- 
Dan