The proposed fix of JDK-8200613 causes an increase in the size of the corefile dumped with CDS on Linux. 
The typical corefile size increase with this would include the following components at a high level:
* Any NIO file mapping with MapMode.PRIVATE.
* Any file mmap()-ed by any native library with MAP_PRIVATE.
* The read only CDS regions (ro and od): Of the order of a few MB.
* The shared strings CDS region. (typically less than 1 MB).
* 2 MB per native shared library (regions with ---p permissions 
mapped by the dynamic linker for better alignment and for keeping 
libraries efficiently shareable).
* The JDK 'modules' file. (About 140 MB).

To control the increase in the corefile size, the modules file is being unmapped as a part of the proposed fix for JDK-8200613.
We need to unmap the NIO file mappings with MapMode.PRIVATE too.