RFR: 8200228: Change default value of HeapSizePerGCThread

[Stefan Johansson]

Hi,

Please review this change of the default value for HeapSizePerGCThread.

Links
JBS: https://bugs.openjdk.java.net/browse/JDK-8200228
Webrev: http://cr.openjdk.java.net/~sjohanss/8200228/00/

Summary
My testing shows that for DaCapo, SpecJVM98 and GCBasher (gc intensive 
stress test) with small heaps we get better pause times with the flag 
set to 32M. There might be other arguments, such as not using to much 
resources on small systems that might also be important so please let me 
know if you have reasons why the flag should be left unchanged.

Thanks,
Stefan