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.
> 
> -Aleksey
> 

The allocation interface change should be backportable and not increase
exposure very significantly (remove some here, add some there). Pulling
in the plab stuff without it would also pull in at least half of the
allocation path interface changes (everything that has to do with
virtualizing fill_with_object() ).

Roman