core.thread.Fiber --- runtime stack overflow unlike goroutines

[Sean Kelly via Digitalmars-d-learn]

At least on OSX, it appears that mapping memory is constant time 
regardless of size, but there is some max total memory I'm 
allowed to map, presumably based on the size of a vmm lookup 
tabe.  The max block size I can allocate is 1 GB, and I can 
allocate roughly 131,000 of these blocks before getting an out of 
memory error.  If I reduce the block size to 4 MB I can allocate 
more than 10M blocks without error.  I think some default stack 
size around 4 MB seems about right.  Increasing the size to 16 MB 
failed after about 800,000 allocations, which isn't enough 
(potential) fibers.