Keeping data from memory mapped files

[Alexibu via Digitalmars-d-learn]

Why do I need to copy data out of memory mapped files to avoid 
seg faults.
This defeats the purpose of memory mapped files.
Shouldn't the GC be able to manage it if I keep a pointer into it.
I am closing them because the OS has a limit in how many it can 
open, either way the memory is still there isn't it ?