RFR: 8337217: Port VirtualMemoryTracker to use VMATree

[Johan Sjölen]

On Mon, 5 Aug 2024 16:50:00 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

>> The bool argument is just passed along.
>> 
>> ```c++
>>   RegionsTree(bool with_storage) : VMATree(), _ncs_storage(with_storage) {
>>   }
>
> Done.
> For my curiosity, what is the advantage?

1. No malloc
2. No indirection, so no cache misses
3. A clear lifetime and clear ownership, both are bound to the `RegionsTree` object

>> Then just invert it: Have the outer class be static and the inner class be an instance. We can change the `MemoryFileTracker` to be that, as it's not as large of a change.
>
> It is still a big change. Why not another RFE?

Because we want to switch to a new way of exposing the public interface, as opposed to an under-the-hood optimization. This PR is still in draft and we're far away from next RDP1, we're not in a hurry and can afford to get this right. I do not want to repeat the same mistakes of the old codebase.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1711099968
PR Review Comment: https://git.openjdk.org/jdk/pull/20425#discussion_r1711190300