RFR: Use PLAB for evacuations instead of TLAB

[Aleksey Shipilev]

On 05/11/2018 03:29 PM, Roman Kennke wrote:
> 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 ;-)

Yes, please. I think it would be cleaner for all codebases. This PLAB change should be independent,
and *then* we can clean it up with saner allocation path for sh/jdk and upstream.

-Aleksey