How ZGC allocates memory for the Java heap

For relevant upcoming changes see Automatic Heap Sizing for ZGC: https://openjdk.org/jeps/8329758

The 32x virtual memory to physical memory ratio plays into relocation and colored pointers (i.e pointers where some bits serve as flag bits).

Putting the actual data layouts in 44 bits out of 64 is a neat trick which relies on the allocator being aware of the mappings between physical and virtual addresses.

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