RFR: Allow young collection to suspend marking in old generation [v3]

[Roman Kennke]

On Fri, 26 Feb 2021 20:16:57 GMT, earthling-amzn <github.com+71722661+earthling-amzn at openjdk.org> wrote:

>> You should enable GitHub actions in your fork under Settings->Actions->Allow all actions. Then you'll get presubmit-tests which runs a whole bunch of stuff on various platforms. A great sanity check.
>
> Yes, it's looking much more stable now. Hmm, I have actions enabled and I see it running builds on different platforms. I've been abusing this branch/pull request to fix windows and aarch64 builds.

It seems that 'RegisterReferences' is a develop flag and does not exist in release build, which means it cannot be changed by the generational mode (it results in crash). If reference processing really is a concern, then the way out would be to introduce our own flag, e.g. ShenandoahReferenceProcessing, and use that (and set RegisterReferences accordingly in non-release builds). OR, maybe even better, put a method should_process_references() in ShenandoahHeurisitics and override that to return false. OTOH, I just tried a bunch of SPECjvm workloads, and they seem to run fine without disabling reference processing (until they attempt a full-GC which is not yet supported).

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PR: https://git.openjdk.java.net/shenandoah/pull/19