RFR: 8218746: SA: Implement discontiguous bitmap for ZGC

[Erik Österlund]

Hi Stefan,

At ZExternalBitMap line 22:
* Maybe add a bounds check for offsets < 0 as well.

At ZExternalBitMap line 45:
* Remove weird whitespace in argument list.
* Consider inverting the condition to early exit. Don't mind if you 
choose to do that or not.

Otherwise looks good. Don't need another webrev.

Thanks,
/Erik

On 2019-02-11 14:55, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to implement a discontiuous bitmap for ZGC in 
> the SA.
> 
> http://cr.openjdk.java.net/~stefank/8218746/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8218746
> 
> ZGC uses a 16TB virtual memory address range, so the normal scheme to 
> map a bitmap over the entire address range uses too much memory. This 
> patch lazily creates smaller bitmaps per ZPage, when at() or atPut() is 
> called.
> 
> This patch builds upon JDK-8218743.
> 
> Tested with serviceability/sa and manually running Reverse Object 
> Analysis in the SA.
> 
> Thanks,
> StefanK