RFR (S): 8023101 java/lang/management/MemoryMXBean/ResetPeakMemoryUsage.java fails

Mandy Chung mandy.chung at oracle.com
Fri Aug 16 08:30:24 PDT 2013


There isn't a guarantee for Runtime.gc() to reclaim any space.  On the 
other hand, the test relies on the knowledge of our implementation (at 
least serial, parallel, concurrent collectors) does collect the large 
object array that is allocated in the old gen.  With G1, the behavior is 
probably different.  Perhaps another way to fix the test is to attempt 
GC a few times?

Mandy

On 8/16/2013 12:00 AM, Staffan Larsen wrote:
> It maybe only happens with G1, but I don't think there is a guarantee that mbean.gc() will always cause all "freed" objects to be reclaimed. By allowing for the heap usage to be the same both before and after mbean.gc() I was hoping to make the test more stable.
>
> But perhaps someone from the GC side can comment on what the guarantees are for mbean.gc() (which calls Runtime.gc() which calls JVM_GC() which does Universe::heap()->collect(GCCause::_java_lang_system_gc)) ?
>
> Thanks,
> /Staffan
>
> On 15 aug 2013, at 21:41, Mandy Chung <mandy.chung at oracle.com> wrote:
>
>> Hi Staffan,
>>
>> Is this issue specific to G1 such as mbean.gc() doesn't collect the "freed" obj?  The test wants to verify the peak usage won't change when GC frees up some space.
>>
>> Mandy
>>
>> On 8/15/2013 12:05 PM, Staffan Larsen wrote:
>>> Please review this small update to the test. The fix allows for no change in heap usage to happen during a GC.
>>>
>>> webrev: http://cr.openjdk.java.net/~sla/8023101/webrev.00/
>>> bug: http://bugs.sun.com/view_bug.do?bug_id=8023101 (not available yet)
>>> jbs: https://jbs.oracle.com/bugs/browse/JDK-8023101
>>>
>>> Thanks,
>>> /Staffan



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