RFR(XS): 8240591: G1HeapSizingPolicy attempts to compute expansion_amount even when at full capacity

[Ivan Walulya]

Hi all,

Please review a small modification for G1HeapSizingPolicy to return without  computing expansion_amount when heap is already at full capacity. 

JBS: https://bugs.openjdk.java.net/browse/JDK-8240591
Webrev: http://cr.openjdk.java.net/~iwalulya/8240591/00/


//Ivan