RFR: 8274987 G1: reuse the newly allocated G1SegmentedArrayBuffer even if current thread failed the race [v3]

[Thomas Schatzl]

On Thu, 21 Oct 2021 03:58:03 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix cransh on Mac; remove unnecessary code
>
> src/hotspot/share/gc/g1/g1SegmentedArray.inline.hpp line 144:
> 
>> 142:     next->set_next(nullptr);
>> 143:     // reuse the newly allocated or poped buffer by adding it into free buffer list.
>> 144:     _free_buffer_list->add(*next);
> 
> Should we add GlobalCounter::write_synchronize() here? If it's true, I'm a little bit concern about the performance.

I think you are right about needing `write_synchronize` here - I mixed this up with `G1CardSetAllocator` which has the intermediate `_pending_list` to avoid excessive `write_synchronize` calls.

If you think this is too expensive (it might well be!), let's just keep the `delete` for now. We can revisit this change when we have more measurements about this.

Thanks,
  Thomas

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PR: https://git.openjdk.java.net/jdk/pull/6034