RFR (XS) 8245757: Shenandoah: AlwaysPreTouch should not disable heap resizing or uncommits

[Roman Kennke]

Alright, looks good!

Roman

On Mon, 2020-05-25 at 21:28 +0200, Aleksey Shipilev wrote:
> RFE:
>   https://bugs.openjdk.java.net/browse/JDK-8245757
> 
> At present, enabling -XX:+AlwaysPreTouch implicitly disables uncommit
> and sets the heap size to Xmx.
> This is not coherent with the rest of OpenJDK garbage collectors that
> only pretouch when the actual
> commit happens. Shenandoah should do the same. It would still be
> recommended to set -Xmx == -Xms for
> AlwaysPreTouch to work without excess latencies.
> 
> Webrev:
>   https://cr.openjdk.java.net/~shade/8245757/webrev.01/
> 
> Testing: hotspot_gc_shenandoah; ad-hoc perf runs
>