RFR(M): 8000244: G1: Ergonomically set MarkStackSize and use virtual space for global marking stack

[Bengt Rutisson]

Hi John,

On 12/6/12 9:10 PM, John Cuthbertson wrote:
> Hi Bengt,
>
> Thanks for looking over the code again.
>
> I've submitted 8004669 to track the reuse enhancement and I've 
> attached the patch.

Great. Thanks!

Bengt

>
>>> To reuse the previous space we need to cache the ReservedSpace in 
>>> the CMMarkStack instance to re-initialize the _virtual_space. As a 
>>> result we need to provide a default constructor for ReservedSpace.
>>
>>
>> If we move the code in CMMarkStack::allocate() into the constructor 
>> of CMMarkStack we would not need to add a default consturctor to 
>> ReservedSpace. I kind of think it would be more natural to have the 
>> setup in the constructor anyway.
>>
>>> Another concern is that I'm not sure that re-committing the original 
>>> unexpanded space won't cause a problem on some platforms. I've 
>>> tested the code with forced re-commits and it seems to work but 
>>> would rather it was pushed as a separate change.
>>
>> Pushing it as a separate change is definitely a good idea. If 
>> re-committting does not work on a particular platform I guess we are 
>> just back to the old behaviour, right? That a failed expand of the 
>> mark stack will exit the VM.
>>
> That's the idea and the code new code in CMMarkStack::expand() should 
> do that. I've also added the above comments to the CR.
>
> Thanks,
>
> JohnC
>