RFR (M): 8212657: Implementation of JDK-8204089 Promptly Return Unused Committed Memory from G1 [Was: RFR (M): 8212657: Implementation of JDK-8204089 Timely Reduce Unused Committed Memory]

[sangheon.kim at oracle.com]

Hi Thomas,

On 12/6/18 5:54 AM, Thomas Schatzl wrote:
> Hi all,
>
> On Tue, 2018-12-04 at 10:32 +0100, Stefan Johansson wrote:
>> On 2018-12-03 15:30, Thomas Schatzl wrote:
>>> Hi Sangheon,
>>>
> [...]
>>> All fixed.
>>>
>>> http://cr.openjdk.java.net/~tschatzl/8212657/webrev.1_to_2/ (diff)
>>> http://cr.openjdk.java.net/~tschatzl/8212657/webrev.2/ (full)
>> Still good,
>> StefanJ
>    while doing testing of other changes (where I included this change) I
> found that very rarely the test fails.
>
> This happens if the test machine is loaded, and additional heap
> resizing happens due to gctimeratio being too high while we are waiting
> for a periodic gc.
>
> E.g.
>
> - <create garbage>
> - some gcs happen
> - concurrent mark starts
> - g1 finds out that gc time ratio is too high -> expands the heap by
> itself
> - concurrent mark finds that we recently expanded too much, shrinks the
> heap
> - periodic gc finds no more opportunity to shrink -> test fails
>
> I trimmed the test to never do any GC (not allocating anything) by
> setting appropriate startup options but still find opportunity to
> shrink with periodic gcs.
>
> This makes the test much shorter in code and execution time, and much
> more robust. :)
>
> http://cr.openjdk.java.net/~tschatzl/8212657/webrev.2_to_3/ (diff)
> http://cr.openjdk.java.net/~tschatzl/8212657/webrev.3/ (full)
Looks good!

Thanks,
Sangheon


>
> Thanks,
>    Thomas
>
>