RFR: 8157153: TestStressRSetCoarsening fails with OOM

[Stefan Johansson]

On 2016-05-27 13:33, Mikael Gerdin wrote:
> Hi Stefan,
>
> On 2016-05-26 17:20, Stefan Johansson wrote:
>> Hi,
>>
>> Please review this testfix for:
>> https://bugs.openjdk.java.net/browse/JDK-8157153
>>
>> Webrev:
>> http://cr.openjdk.java.net/~sjohanss/8157153/hotspot.00/
>
> Would it be possible to encapsulate the storage[] so that you don't 
> have to put the "% storageUsedCount" all over the place?
> This seems a bit fragile to me.
Thanks for taking a look Mikael. I agree, that my initial fix might 
cause problems and I like how your idea turned out:
Full: http://cr.openjdk.java.net/~sjohanss/8157153/hotspot.01/
Inc: http://cr.openjdk.java.net/~sjohanss/8157153/hotspot.00-01/

Thanks,
Stefan

>
> /Mikael
>
>>
>> Summary:
>> The test sometimes fail due to running out of memory and the reason is
>> that the test expects to be able to fit 2 objects of the size
>> HeapRegionSize/2 into one heap region. This assumption is ok in theory,
>> but if any object at all is allocated between the two allocations the
>> second one will end up in a different region. The test calculates how
>> many regions it should fill to get 90% of the heap used and then
>> allocated twice this number of objects. In many cases this will work
>> since nothing else is going on, but in some cases some other subsystem
>> might start allocating objects, and this destroys the assumptions
>> leading to hitting an OOME.
>>
>> The fix simply adds a second check to the allocation loop to stop as
>> soon as the free memory drops below 10% of the heap, this also requires
>> some extra limiting of the indexes used.
>>
>> Testing:
>> * Local testing as well as runs through RBT.
>>
>> Thanks,
>> Stefan