RFR: 8165955: TestFullGCCount test failed with CMS and -XX:+ExplicitGCInvokesConcurrent

[Michail Chernov]

Hi Thomas,

Thanks for detailed answer. I've filed CR:
https://bugs.openjdk.java.net/browse/JDK-8169784
Thank you for reviewing this.

Michail

On 16/11/2016 16:43, Thomas Schatzl wrote:
> Hi Michail,
>
> On Mon, 2016-11-14 at 15:52 +0300, Michail Chernov wrote:
>> Hi Dima, thank you for reviewing!
>>
>> Could I have a reviewer's review on this change, please?
>    the change looks good.
>
> I looked a bit through the source to see where and how the various
> collectors use TraceMemoryManagerStats, and actually it seems to me the
> reason that G1 can run this test with ExplicitGCInvokesConcurrent is
> that unlike the other collectors it really only uses the
> TraceMemoryManagerStats during a non-marking related pause, while the
> others (particularly CMS) post these statistics at every STW pause.
>
> I can imagine that this means that GC statistics for all tools that use
> these do not get any relevant notifications with G1 for marking related
> STW pauses (remark, cleanup).
>
> This seems to be something that may need to be fixed. Can you file an
> enhancement?
>
> Thanks,
>    Thomas
>
>