RFR: Use PLAB for evacuations instead of TLAB

[Roman Kennke]

Am 11.05.2018 um 14:51 schrieb Aleksey Shipilev:
> On 05/10/2018 09:28 PM, Roman Kennke wrote:
>>>> Diff:
>>>> http://cr.openjdk.java.net/~rkennke/plab-gclab/webrev.03.diff/
>>>> Full:
>>>> http://cr.openjdk.java.net/~rkennke/plab-gclab/webrev.03/
>>>
>>> Looks good.
>>>
>>> -Aleksey
>>>
>>
>> I just realized that it sortof depends on the allocation refactoring
>> (see "Improve abstraction for runtime allocations"):
>>
>> http://mail.openjdk.java.net/pipermail/shenandoah-dev/2018-May/005886.html
>>
>> Re-basing it would mean to get half of that patch into this one. I think
>> it's cleaner as it is.
> 
> Since using PLABs instead of TLABs is something that we want to backport, so it should be separate
> from whatever interface changes we also do. It seems runtime allocations interface would increase
> upstream exposure in backports, and so we better these two changes.
> 


The alternative would be to add some mess similar to what we have in
TLAB now to adjust fill_with_object() and initialize the fwd pointer,
etc. I can do that -- after lunch ;-)

Roman