RFR: 8337217: Port VirtualMemoryTracker to use VMATree [v32]

[Johan Sjölen]

On Fri, 28 Feb 2025 19:51:20 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> The `HeapReserver` and `MemoryFileTracker` classes (in different parts of the code and different PRs) also use the same syntax for it. Here the same style is used to keep similarity in Hotspot code.
>
> Right, I didn't like it before, and spoke out against it, and now it is spreading :-)
> 
> Why do we want to have more than one VMT? If we truly do, then I'm not sure there is anything that could be done here.

We want to have many because it makes unit testing easier and more reliable, there is no longer any need to access the global object which the rest of the VM is working with. There are more advantages: Each member does not have to be static and a pointer which is initialized separately, everything is under one call to malloc. That reduces the number of pointers, keeping the lifetimes of the objects trivial. I'll pay some verbosity for that any day :-).

If we find an alternative, can it wait with being implemented until this is integrated?

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PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1976500876