RFR: 8222145: Add -XX:SoftMaxHeapSize flag

[Thomas Schatzl]

Hi,

On Wed, 2019-04-10 at 14:06 +0200, Per Liden wrote:
> Introduce a manageable SoftMaxHeapSize flag. When set, the GC should 
> strive to not grow heap size beyond the specified size. But as the
> flag name suggests, this is a soft limit. In other words, the GC is
> allowed to grow the heap size beyond SoftMaxHeapSize if needed.
> 
> There are a few different use cases where this flag could be useful.
> For example, when you want to keep the heap footprint down, while
> retaining the capability to deal with a temporary increase in heap
> space requirement. Or when you want to play it safe, with lots of
> margin, to increase confidence that you will not run into an
> allocation stall because of an unforeseen increase in allocation
> rate.
> 
> The SoftMaxHeapSize should not be allowed to be set to a value
> smaller than min heap size (-Xms) or greater than max heap size (-
> Xmx). When not set on the command-line, this flag should default to
> the max heap size.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8222145
> CSR: https://bugs.openjdk.java.net/browse/JDK-8222181
> Webrev: http://cr.openjdk.java.net/~pliden/8222145/webrev.1
> 

  looks good to me.

Thomas