CRR: 7032531: G1: enhance GC logging to include more accurate eden / survivor size transitions (S/XS)

[Tony Printezis]

Hi all,

Could I have a couple of reviews for this change?

http://cr.openjdk.java.net/~tonyp/7032531/webrev.0/

This enhances the G1 +PrintGCDetails output to include how much space 
there is in the eden and survivor regions before / after a GC. Here's an 
example of the output:

    [Eden: 18M->0B Survivors: 1024K->2048K Heap: 27M(105M)->12M(125M)]

It shows that the eden had 18MB before the GC and it's empty after it 
(as expected!), the survivors were 1MB before the GC and grew to 2MB 
after the GC, the used space in the heap fell from 27MB to 12MB, and 
finally the heap size grew from 105MB to 125MB.

Note that, currently, the eden / survivor sizes that are reported are 
not very accurate. They are currently calculated as region_num * 
region_size. It'd be better if they were calculated as the used byte 
total in the eden and survivor regions. But this would require a fair 
amount of extra changes to do (I'd rather avoid iterating over them to 
calculate that). We'll do that change when we revamp the region lists 
that keep track of the eden / survivor regions (which is currently 
work-in-progress).

Tony