RFR: Use PLAB for evacuations instead of TLAB

[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.

-Aleksey