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

sangheon.kim at oracle.com sangheon.kim at oracle.com
Mon Oct 29 22:18:29 UTC 2018

Hi Thomas,

On 10/2/18 8:57 AM, 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/
Looks good.
Just minor nits so okay going with current webrev. And I don't need 
extra webrev if you accept it.


4399 assert(r->rem_set()->is_empty(), "Remembered sets should be empty.");

4404 assert(r->rem_set()->is_empty(), "Remembered sets should be empty.");

- Can we differentiate newly added 2 same assert? This can be 
'Remembered sets should be empty, if the region is empty'.

- Copyright update


> Testing:
> hs-tier1-5, jdk-tier1-3, perf testing ongoing but not expecting a
> difference
> Thanks,
>    Thomas

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