RFR: Move ShHeap::used increment out of locked allocation path

[Roman Kennke]

Am 06.04.2018 um 18:40 schrieb Aleksey Shipilev:
> On 04/06/2018 06:25 PM, Roman Kennke wrote:
>> Am 06.04.2018 um 17:31 schrieb Aleksey Shipilev:
>>> http://cr.openjdk.java.net/~shade/shenandoah/alloc-move-used/webrev.01/
>>>
>>> Slowly moving more things out of the locked allocation path, to make contention less painful, and to
>>> shrink locked region to ultimately eliminate it. This moves the ShHeap::used() handling to lock-free
>>> path.
>>>
>>> Thanks,
>>> -Aleksey
>>>
>>
>> Good!
>>
>> I believe there's Atomic::sub() for stuff like Atomic::add(-bytes, &_used).
> 
> Alas, not in backports, so we have to use Atomic::add. I have a todo item to make add proper counter
> to shenandoahSharedVariables to avoid these things.

Right. Good then!

Thanks,
Roman