RFR 8020467: Inconsistency between usage.getUsed() and isUsageThresholdExceeded() with CMS Old Gen pool

[Jaroslav Bachorik]

On 22.10.2013 22:04, Mandy Chung wrote:
> Hi Jaroslav,
>
> On 10/22/13 6:47 AM, Jaroslav Bachorik wrote:
>> Please, review the following test fix:
>>
>> Issue:  https://bugs.openjdk.java.net/browse/JDK-8020467
>> Webrev: http://cr.openjdk.java.net/~jbachorik/8020467/webrev.01
>>
>
> Have you considered to force GC when getUsed() == 0 regardless of which
> memory pool it is?  This will avoid special casing for CMS old gen in
> the test and will handle similar issue in the future for a different
> collector implementation.  To make the test reliable, the test should
> still pass if the memory pool has no object in it (G1 survivor space
> case?).

Hi Mandy,

I don't know whether GC will help for other pools - but I can enable it 
for all pools - it should not hurt.

The test should pass even with on object in the monitored pool since the 
pool should not report an exceeded threshold.

-JB-

>
> Mandy
>
>> The test tries to make sure that the "pool usage threshold" trigger
>> and the reported pool memory usage are not contradicting each other.
>> The problem is that it is not possible to get the "pool usage
>> threshold exceeded" flag and the pool memory usage atomicly in regard
>> to the GC. Specifically, when "CMS Old Gen" pool is examined and the
>> usage is retrieved before a GC promotes some objects to the old gen
>> but the usage threshold is checked after the GC has promoted some
>> instance into the old gen the test will fail.
>>
>> The patch makes sure that there are some instances promoted in "CMS
>> Old Gen" before checking the "pool usage threshold" to get
>> semi-consistent view.
>>
>> Thanks,
>>
>> -JB-
>