After JDK-8231610 (Relocate the CDS archive if it cannot be mapped to the requested address), we will have a new "bm" region that's used only during archive loading, and will be unmapped afterwards to save memory footprint. This region will be a good place for the CDSFileMapRegion::oopmap, which is also needed only during archive loading.

http://hg.openjdk.java.net/jdk/jdk/file/13ad9a1bac18/src/hotspot/share/include/cds.h#l53