RFR: 8256181: Remove Allocation of old generation on alternate memory devices functionality [v2]

[Ioi Lam]

On Wed, 11 Nov 2020 15:19:05 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   ayang review
>
> A general comment for future PRs: I think it's best to isolate mechanical changes into their own commits; e.g. `HeapRegionManager* _hrm;` -> `HeapRegionManager _hrm;`. Otherwise, a real change, buried in the immense size of diff, might slip through.

This is a good fix. It removes the dependency on the problematic API `ReservedSpace::first_part(..., split=true)`, which cannot be implemented correctly on Windows (see [JDK-8256079](https://bugs.openjdk.java.net/browse/JDK-8256079)). This API is used only by CDS (to be removed in [JDK-8255917](https://bugs.openjdk.java.net/browse/JDK-8255917)) and heterogenous heap. So hopefully we can remove this problematic API soon.

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PR: https://git.openjdk.java.net/jdk/pull/1162