RFR: 8366363: MemBaseline accesses VMT without using lock [v2]

[Afshin Zafari]

On Mon, 1 Sep 2025 13:22:03 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Hi,
>> 
>> The `MemBaseline` used to access the VMT instance directly without a lock. We fix that, and we switch from using a `LinkedList` to a copied `RegionsTree` instead.
>
> Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Static assert copy-constructible

Thank you @jdksjolen for taking this issue. 
I have only one concern when we copy a RBTree to a new one. We do a `visit_in_order` on the source tree and `upsert` the key-value to the destination tree. We do a sorted access on both trees. We can avoid one, by  a new function like: `visit_all()` for the source tree, or for the destination tree use the `hint_node` somehow (that I don't know how, ping @caspernorrbin) in `RBTree::upsert(K, V, Node* hint_node)`

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PR Review: https://git.openjdk.org/jdk/pull/27003#pullrequestreview-3175564256