RFR: 8262398: Shenandoah: Disable nmethod barrier and stack watermark when running with passive mode [v3]

[Aleksey Shipilev]

On Tue, 16 Mar 2021 16:58:23 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> nmethod barrier and stack watermark allow GC not to process nmethods at GC pauses, and aim to reduce GC latency, they do not benefit STW GCs, who process nmethods at pauses anyway.
>> 
>> Test:
>> 
>> - [x] hotspot_gc_shenandoah
>> - [x] tier1 with -XX:+UseShenandoahGC
>> - [x] tier1 with -XX:+UseShenandoahGC -XX:ShenandoahGCMode=passive
>> - [x]  tier1 with -XX:+UseShenandoahGC -XX:ShenandoahGCMode=passive -XX:-ShenandoahDegeneratedGC
>
> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Aleksey's comments

Marked as reviewed by shade (Reviewer).

test/hotspot/jtreg/gc/shenandoah/options/TestSelectiveBarrierFlags.java line 50:

> 48:                 new String[] { "ShenandoahCloneBarrier" },
> 49:                 new String[] { "ShenandoahNMethodBarrier"},
> 50:                 new String[] { "ShenandoahStackWatermarkBarrier"}

Note there is a space between `"` and `}`. Minor nit, fix before push.

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