RFR: 8231552: ZGC: Refine address space reservation

[Per Liden]

Another update after Stefan found an incorrect comparison:

Full: http://cr.openjdk.java.net/~pliden/8231552/webrev.4
Diff: http://cr.openjdk.java.net/~pliden/8231552/webrev.4-diff

/Per

On 10/22/19 2:01 PM, Per Liden wrote:
> Updated webrev after off-line comments from Stefan and Erik.
> 
> Full: http://cr.openjdk.java.net/~pliden/8231552/webrev.3
> Diff: http://cr.openjdk.java.net/~pliden/8231552/webrev.3-diff
> 
> /Per
> 
> On 10/16/19 10:41 AM, Per Liden wrote:
>> Latest version of this patch, rebased on today's jdk/jdk:
>>
>> http://cr.openjdk.java.net/~pliden/8231552/webrev.2
>>
>> /Per
>>
>> On 10/3/19 11:45 AM, Per Liden wrote:
>>> We could be slightly more sophisticated and do a better job reserving 
>>> address space in situations where parts of the address space is 
>>> already occupied or when the process is running with address space 
>>> limitations.
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8231552
>>> Webrev: http://cr.openjdk.java.net/~pliden/8231552/webrev.0
>>>
>>> /Per