RFR: 8218733: SA: CollectedHeap provides broken implementation for used() and capacity()

[Jini George]

Hi Stefan,

Looks good to me.

Thanks,
Jini.

On 2/11/2019 1:43 PM, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to remove the broken implementation of 
> CollectedHeap used() and capacity() and instead force all GCs to provide 
> their own implementations.
> 
> https://cr.openjdk.java.net/~stefank/8218733/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8218733
> 
> This was found while running 
> serviceability/sa/TestHeapDumpForLargeArray.java on an experimental 
> implementation of heap dumping in ZGC.
> 
> ZGC didn't provide a ZCollectedHeap.used() function and 
> CollectedHeap.used() was used instead at:
>          // Check weather we should dump the heap as segments
>          useSegmentedHeapDump = vm.getUniverse().heap().used() > 
> HPROF_SEGMENTED_HEAP_DUMP_THRESHOLD;
> 
> Because of this we incorrectly did not use segmented heap dumps, and 
> therefore overflowed later in the code
> 
> Aleksey and Roman,
> 
> Could you verify that the implementation for Epsilon is correct? I also 
> haven't implemented capacity for Shenandoah, as the information isn't 
> trivially available in the ShenandoahHeap SA class. Do you want to fix 
> it as part of this patch, or should I create a separate RFE for Shenandoah?
> 
> Thanks,
> StefanK