RFR: Marking and evacuation constrained to young gen in generational mode.

[Roman Kennke]

On Wed, 9 Dec 2020 16:40:42 GMT, Bernd Mathiske <bmathiske at openjdk.org> wrote:

> These restrictions will change when we have multiple generations at work. For GenShen milestone 1 we want to operate entirely in the young generation, to prove our changes function thus far.
> 
> The second commit adds the missing generation affiliation for contiguous allocations, i.e. humongous object regions.
> 
> This step still runs normally when in any non-generational mode, and it runs at reduced heap capacity in generational mode. Only the young generation is populated in the latter case.

Looks good. Thanks!

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Marked as reviewed by rkennke (Reviewer).

PR: https://git.openjdk.java.net/shenandoah/pull/9