RFR (S): 6490394: G1: Allow heap shrinking / memory unmapping after reclaiming regions during Remark

[Thomas Schatzl]

Hi,

  ping for a second review..

Thomas

On Tue, 2018-10-02 at 17:57 +0200, Thomas Schatzl wrote:
> Hi all,
> 
>   allow me to provide a fix for the oldest g1-specific open issue on
> the bug tracker (from 2006 :)): resize the heap (eg. uncommit)
> according to existing sizing policies at remark time.
> 
> It does exactly what the subject of the CR says.
> 
> The feature is enabled by default - I did not see any reason to
> disable
> it as the functionality seems to actually be what would be expected
> of
> the concurrent cycle (as it mirrors the functionality of a full gc).
> 
> Needs the change for JDK-8071913 currently out for review applied to
> work (i.e. not crash after uncommit).
> 
> The current work for "JDK-8204089: Timely Reducing Unused Committed
> Memory" also depends on this change.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-6490394
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/6490394/webrev/
> Testing:
> hs-tier1-5, jdk-tier1-3, perf testing ongoing but not expecting a
> difference
> 
> Thanks,
>   Thomas
> 
> 
>