RFR: JDK-8211270: GC abstraction to get real object and headers size

Zhengyu Gu zgu at redhat.com
Tue Oct 9 23:07:47 UTC 2018


Looks good to me.

Thanks,

-Zhengyu

On 10/09/2018 10:39 AM, Roman Kennke wrote:
> Hey Aleksey,
> 
>> On 10/05/2018 06:20 PM, Roman Kennke wrote:
>>>> Webrev:
>>>> http://cr.openjdk.java.net/~rkennke/JDK-8211270/webrev.00/
>>
>> Do we really need the abstractions for header sizes? I think all usages need the object size, and
>> header sizes can be just picked up from the usual places. No GC, including Shenandoah is changing
>> the header size?
>>
>> Trying to understand the use case, looking at Shenandoah's diff here:
>>
>> https://builds.shipilev.net/patch-openjdk-shenandoah-jdk/latest/src/hotspot/share/gc/shared/plab.cpp.sdiff.html
>>
>> ...it seems what we really want is to mix in oop_extra_words into plab.cpp accessors. Because doing
>> ShenandoahHeap::obj_header_size() { return obj_header_size + oop_extra_words; } seems wrong down the
>> line -- it would _not_ be the header size.
> 
> It seems that the PLAB stuff does indeed require a different kind of
> abstraction, and most likely something that can be shared with, e.g.,
> TLAB in the form of a virtual version of CollectedHeap::min_fill_size()
> or such. Let's take this part out of the patch:
> 
> http://cr.openjdk.java.net/~rkennke/JDK-8211270/webrev.01/
> 
> Good now?
> 
> Roman
> 


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