RFR: 8252752: Clear card table for old regions during scan in G1 [v2]

[Thomas Schatzl]

On Fri, 25 Sep 2020 12:46:59 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Comments by ayang, kbarrett, iwalulya
>
> Marked as reviewed by ayang (Author).

@albertnetymk, @kimbarrett, @walulyai, thanks for your reviews.

Thomas

> src/hotspot/share/gc/g1/g1CollectedHeap.hpp line 787:
> 
>> 785:   // The may_do_optional_evacuation flag indicates whether some or more optional evacuation
>> 786:   // steps will follow.
>> 787:   void evacuate_initial_collection_set(G1ParScanThreadStateSet* per_thread_states,
> 
> The PR description provides a very good motivation for this patch, and I think such motivation should be reprinted here
> to explain **why** we are interested in tracking if there is an optional evac.

I added a little bit of motivation. I am planning to write up more about the card scanning and the various motivations
in a better place. I hope the text that is now there is sufficient.

Thanks for your review.

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PR: https://git.openjdk.java.net/jdk/pull/343