RFR: 8276887: G1: Move precleaning to Concurrent Mark From Roots subphase [v5]

[Kim Barrett]

On Sun, 14 Nov 2021 23:08:09 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Simple change of moving the "Preclean" subphase into "Mark from roots" subphase so that precleaning becomes parallel automatically. Evaluation using a contrived java program shows that multiple GC threads do precleaning. More detailed testing results are available in the JBS ticket.
>> 
>> Test: hotspot_gc
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

Looks good.

-------------

Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6327