RFR: 8199407: Skip Rebuild Remset Phase if there are no rebuild candidates

[Ivan Walulya]

On Mon, 12 Apr 2021 12:55:14 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Hi all,
>> 
>> Please review this change that skips the rebuild remset phase and the associated updates after rebuild, If during Remark, G1 finds that there are no remembered sets to rebuild.
>> 
>> Test: tier1-5
>
> src/hotspot/share/gc/g1/g1ConcurrentMark.cpp line 1324:
> 
>> 1322: 
>> 1323:   verify_during_pause(G1HeapVerifier::G1VerifyCleanup, VerifyOption_G1UsePrevMarking, "Cleanup before");
>> 1324:   bool has_rebuilt_remembered_sets = (total_selected_for_rebuild() > 0);
> 
> Please add a newline before.

noted, thanks

> src/hotspot/share/gc/g1/g1ConcurrentMark.hpp line 460:
> 
>> 458:   // set phase at all.
>> 459:   HeapWord* volatile* _top_at_rebuild_starts;
>> 460:   uint _total_selected_for_rebuild;
> 
> Something like `// Number of regions selected for rebuild in the Remark pause` should be added here.
> It seems unnecessary to actually store that number, but sufficient that there is any need to rebuild regions. That would simplify the conditions in two places.

Indeed, a bool has_rebuilt_remembered_sets should suffice.

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PR: https://git.openjdk.java.net/jdk/pull/3434