RFR(XS): Heap memory usage counting not longer needs to be atomic

[Aleksey Shipilev]

On 02/22/2017 09:00 PM, Zhengyu Gu wrote:
> On 02/22/2017 02:53 PM, Aleksey Shipilev wrote:
> 
>> On 02/22/2017 08:45 PM, Zhengyu Gu wrote:
>>> After guarding memory allocation with heap lock, memory usage counting also
>>> under heap lock
>>> or executed by VM thread during a safepoint.
>>>
>>> http://cr.openjdk.java.net/~zgu/shenandoah/memory_counting/webrev.00/
>> Not sure.
>>
>> There is ShenandoahMonitoringSupport::update_counters() that polls these outside
>> safepoint. Tried with -XX:+UsePerfData -XX:+ShenandoahRegionSampling? I am
>> pretty sure that some JMX/JvmStat counters would eventually do this too.
> 
> Yes, I did. There is only a read, not updates.

Ok!

I am uneasy about naked reads without any sort of barrier. Is there a compiler
barrier at least?

Thanks,
-Aleksey