RFR: 8262398: Shenandoah: Disable nmethod barrier and stack watermark when running with passive mode [v2]

[Aleksey Shipilev]

On Tue, 16 Mar 2021 15:14:05 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Zhengyu Gu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
>> 
>>  - Uses flags instead of mode
>>  - Merge branch 'master' into JDK-8262398-disable-barriers-stw-gc
>>  - JDK-8262398
>>  - init
>
> Yes, thank you. A few minor nits below.

Forgot one thing. These tests might also need modification to test that we never disable this for true heuristics, etc.

./test/hotspot/jtreg/gc/shenandoah/options/TestSelectiveBarrierFlags.java
./test/hotspot/jtreg/gc/shenandoah/options/TestWrongBarrierEnable.java
./test/hotspot/jtreg/gc/shenandoah/options/TestWrongBarrierDisable.java

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PR: https://git.openjdk.java.net/jdk/pull/2727