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

[Roman Kennke]

Am 22.02.2017 um 21:03 schrieb 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?

Is there anything that prevents us from updating the counters under the
same lock?

Roman