If NMT is enabled with gtests (which only can be done with the upcoming JDK-8256844 "Make NMT late-initializable", for which I have a working prototype) we run into new problems with NMT.

One of which is that NMT assumes that we only release regions or parts of regions, but not multiple regions.

Which is perfectly possible, e.g. we can reserve several adjacent regions and release them in one go. Which is done e.g. in the context of NUMA-aware allocation.

To test such a multi-map release, I added a gtest: os_release_multi_mappings_vm. This one runs into an NMT assert with NMT enabled:

# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/shared/projects/openjdk/jdk-jdk/source/src/hotspot/share/services/virtualMemoryTracker.cpp:533), pid=264733, tid=264733
# assert(reserved_rgn->contain_region(addr, size)) failed: Not completely contained

which highlights NMTs inability to deal with that.

This surfaces as an assert in a gtest but is of course not limited to gtests.