RFR: Handle old, pinned regions [v7]

[William Kemper]

On Fri, 5 Aug 2022 07:00:01 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> William Kemper has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 21 commits:
>> 
>>  - Merge branch 'shenandoah-master' into fill-old-pinned
>>  - Do not drop abbreviated argument when recording success concurrent cycle
>>  - Fix whitespace
>>  - Prepare for review
>>  - Merge branch 'shenandoah-master' into fill-old-pinned
>>  - Validate old gen state transitions
>>  - Make use of old generation without down casting
>>  - Make verifier aware of changes to old generation state machine
>>  - Make rset scan aware of changes to old generation state machine
>>  - Fix use of index as count and over-counting of garbage
>>  - ... and 11 more: https://git.openjdk.org/shenandoah/compare/60e43d04...bdda91d6
>
> src/hotspot/share/gc/shenandoah/heuristics/shenandoahOldHeuristics.cpp line 212:
> 
>> 210:     if (region->is_regular() || region->is_pinned()) {
>> 211:       if (!region->has_live()) {
>> 212:         assert(!region->is_pinned(), "Pinned region should have live (pinned) objects.");
> 
> This comment pertains to lines 231-234 below for the case where the immediate_regions and immediate_garbage for the humongous regions are being counted. I think while it correctly counts the contribution of the Humongous Continuations, I believe because of the "else if" it misses the contribution of the first Humongous Starts region. 
> 
> This isn't a serious issue, however, since it's just a value that is logged rather than being used in guiding any steps/heuristics in the collection. Not your change, but thought I'd mention it.

That's a good catch! Eventually we could have a threshold for the amount of `immediate_garbage` above which we would _not_ continue with the old collection (i.e., we found enough immediate garbage to skip mixed collections). I will open a separate PR to fix this.

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PR: https://git.openjdk.org/shenandoah/pull/149