RFR: 8031686: G1: assert(_hrs.max_length() == _expansion_regions) failed

[Stefan Johansson]

Hi,

I've got some comments offline about the test and my initial assumption 
that more than one GC would be tested the way the test was written might 
have been wrong. I've now made the test a G1 only regression test, to 
specifically test the issue reported in this bug.

New webrev:
http://cr.openjdk.java.net/~sjohanss/8031686/webrev.02/

Thanks,
Stefan

On 2014-01-17 15:23, Stefan Johansson wrote:
> Hi again,
>
> I've added a regression test for the issue. See the updated review at:
> http://cr.openjdk.java.net/~sjohanss/8031686/webrev.01/
>
> The test is naive and just tries to run -version with a heap size of 
> 2g. I don't explicitly set G1 as GC but make sure I will use the 
> arguments given to jtreg, this will ensure testing more than one GC 
> and also that we do not run with G1 on unsupported platforms.
>
> Please have a look at the test and let me know if you have any 
> questions or suggestions.
>
> Thanks,
> Stefan
>
> On 2014-01-16 14:43, Stefan Johansson wrote:
>> Hi,
>>
>> Please review this small fix for:
>> https://bugs.openjdk.java.net/browse/JDK-8031686
>>
>> Webrev:
>> http://cr.openjdk.java.net/~sjohanss/8031686/webrev.00/
>>
>> Summary:
>> The failing assertion is caused by an erroneous calculation done when 
>> setting up the regions array in HeapRegionSeq. When using a large 
>> heap a pointer calculation will overflow (since ptrdiff_t is signed) 
>> and this will in turn lead to the regions array being created longer 
>> that it should be. For non debug builds this will lead to increased 
>> memory usage and jmap will report a faulty value for the number of 
>> regions. The fix is to use the pointer_delta-function to do the 
>> calculation.
>>
>> Note: The bug is currently targeted for 8 but is defer-requested and 
>> should be moved to 9 shortly. I plan to fix it in 9 and backport it 
>> to 8u20.
>>
>> Testing:
>> * Manually verified that we are able to start 32-bit VMs with more 
>> than 2g of heap using a debug build.
>>
>> Thanks,
>> Stefan
>