RFR: JDK-8297796 GenShen: instrument the remembered set scan [v15]

[Kelvin Nilsen]

On Tue, 27 Dec 2022 21:53:12 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> Y. Srinivas Ramakrishna has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 68 commits:
>> 
>>  - Merge branch 'master' into JVM-1264
>>  - A couple of changes based on review feedback.
>>  - Reword some code comments for greater clarity.
>>  - Merge branch 'master' into JVM-1264-dependent
>>  - Add a previously missed ticket#. Doing it here rather than in parent to
>>    avoid an otherwise unnecessary re-review touchpoint.
>>  - Merge branch 'stats_merge' into JVM-1264-dependent
>>  - Merge branch 'master' into stats_merge
>>  - jcheck space fix
>>  - Fix compiler error on windows.
>>  - Fix some tier1 tests.
>>  - ... and 58 more: https://git.openjdk.org/shenandoah/compare/d793fd16...4e5ad4ca
>
> src/hotspot/share/gc/shenandoah/shenandoahScanRemembered.cpp line 83:
> 
>> 81:   _rp->set_mark_closure(worker_id, &cl);
>> 82:   struct ShenandoahRegionChunk assignment;
>> 83:   while (_work_list->next(&assignment)) {
> 
> No need for a code change here, but just want to make clear that we may want to enable cancellation of rem-set scanning at some future time.  The primary benefit would be to allow quicker transition to Full GC in the case that we have to degenerate.

This would also accelerate the transition to degenerated mode, so we can get ourselves out of the STW pause more quickly.

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PR: https://git.openjdk.org/shenandoah/pull/176