That's most likely reserved virtual memory. It's not committed, meaning it's not backed by physical memory.
Required simply by ZGC to work, but still its super confusing and convoluted and our tooling is not aware of that at all.
I wouldn't say that tooling is not aware of all that. For example, top and htop display virtual memory and resident memory and shared memory. You need to look at resident memory if you want to know physical memory usage.
Best you can do is do dumps, verify, enable NMT, verify.
It gives me no value to know that my heap is 60m, but my RSS is 600mb while reserved is 40GB. Need more details and those are not always provided i.e. “Unknown” category in NMT details.
Best is that top, pmap and nmt are all showing completely different values for resident size :> and its not a unit issue.