RFR: Humongous top() should be correct for iteration

[Zhengyu Gu]

Looks good.

-Zhengyu

On 09/12/2017 08:38 AM, Aleksey Shipilev wrote:
> Setting ShenandoahHumongousThreshold=90 starts to crash VM during object iteration. This happens
> because we set "top" to "end" in humongous allocation path, and iteration uses that as the scanning
> boundary. This is incorrect with non-full humongous start region, which does not have anything past
> the actual object. While fixing that, we can also make humongous regions report their true use
> (because we put correct "top") and liveness.
> 
> Fix:
>    http://cr.openjdk.java.net/~shade/shenandoah/humongous-use/webrev.02/
> 
> Testing: hotspot_gc_shenandoah + added failing config to the test
> 
> Thanks,
> -Aleksey
>