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

Jon Masamitsu jon.masamitsu at oracle.com
Fri Aug 16 07:39:22 PDT 2013


Stafan,

There is a GC flag ExplicitGCInvokesConcurrent which causes a system.GC() to
be done concurrently.  This means that the application can be allocating 
during
a GC so heap usage can go up.  This affects both CMS and G1.  Were you
aware of this option and its consequences?

Ask more questions if I missed the point here.

Jon

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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