RFR: 8272138: ZGC: Adopt relaxed ordering for self-healing [v5]

[Albert Mingkun Yang]

On Wed, 11 Aug 2021 03:47:59 GMT, Hao Tang <github.com+7947546+tanghaoth90 at openjdk.org> wrote:

>> Xiaowei Lu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   replace release() to a single place in insert()
>
> src/hotspot/share/gc/z/zForwarding.inline.hpp line 141:
> 
>> 139:   // Make sure that object copy is finished
>> 140:   // before forwarding table installation
>> 141:   OrderAccess::release();
> 
> Can we replace it by `OrderAccess::storestore()`? I think LoadStore constraint in `OrderAccess::release()` is not required here.
> Furthermore, is it possible to relax `Atomic::load_acquire` in `ZForwarding::at`?

I believe further relaxing is possible, but it's unclear whether there will be observable perf improvement. Could be interesting to see some numbers before drawing any conclusion.

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PR: https://git.openjdk.java.net/jdk/pull/5046