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

[Thomas Schatzl]

Hi,

On 10.10.20 00:29, Thomas Schatzl 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

   after some chat with Stefan we agreed on above version.

Since this revision has been created in direct conversation with Stefan, 
and Kim already approved it, I'll integrate it.

Thanks for your reviews.

Thanks,
   Thomas