RFR: 8254028: G1 incorrectly updates scan_top for collection set regions during preparation of evacuation [v3]

[Kim Barrett]

On Fri, 9 Oct 2020 22:29:19 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Hi all,
>> 
>>   can I have reviews for this change that makes values of G1RemSetScanState::_scan_top for regions in the initial
>>   collection set consistent with ones in optional collection set?
>> So currently G1RemSetScanState::_scan_top is top() for regions in the initial collection set although they will never
>> be scanned as enforced when dropping the remsets onto the card table. For the optional collection set, G1 sets scan_top
>> manually to NULL when selecting the next few optional regions (using G1RemSet::exclude_region_from_scan()).  When
>> debugging this discrepancy recently posed some slight surprise for me, so I would like to change this. Also there is
>> some risk that future code that relies on that property will be surprised.  Testing: tier1-4; lots of kitchensink runs
>> with JDK-8254164.
>> Thanks,
>>   Thomas
>
> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   sjohanss review

Marked as reviewed by kbarrett (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/557