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

[sangheon.kim at oracle.com]

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.

-----------------------------------------
src/hotspot/share/gc/g1/g1CollectedHeap.cpp

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'.


-----------------------------------------
test/hotspot/jtreg/gc/g1/humongousObjects/objectGraphTest/TestObjectGraphAfterGC.java
- Copyright update

Thanks,
Sangheon


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

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