RFR: Degenerate to young cycles for out of cycle allocation failures

[Kelvin Nilsen]

On Mon, 18 Oct 2021 21:47:44 GMT, William Kemper <wkemper at openjdk.org> wrote:

> ### Summary
> * Allocation failures outside of cycle degenerate to young collections (previously we ran a global cycle)
> * Added new degen point "roots" because remembered set swap during init mark is _not_ idempotent
> * There is also a change here to register old gen objects when they are allocated under a lock (this reverts a previous change)

Marked as reviewed by kdnilsen (Committer).

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PR: https://git.openjdk.java.net/shenandoah/pull/91