RFR: 8221786: ZGC: Increase max heap size to 16TB

[Per Liden]

Updated webrev after StefanK spotted errors in the ASCII diagrams.

http://cr.openjdk.java.net/~pliden/8221786/webrev.1

/Per

On 4/1/19 10:14 PM, Per Liden wrote:
> Increase max heap size to 16TB. We could just bump 
> ZPlatformAddressOffsetBits to 44, but we should take the opportunity to 
> make this slightly more dynamic and set ZPlatformAddressOffsetBits at 
> runtime. As a start, I propose that we limit the dynamic behavior to an 
> address space reservation of 4TB, 8TB or 16TB (per heap view), depending 
> on what -Xmx is set to. In the future we could have a more elaborate 
> scheme if we find a need for that.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8221786
> Webrev: http://cr.openjdk.java.net/~pliden/8221786/webrev.0
> 
> /Per