[RFC] ZGC proposal for aarch64 jdk11u

Per Liden per.liden at oracle.com
Thu Jan 16 08:22:33 UTC 2020


Hi,

ZGC in JDK 11 is fairly stable as it is, so there's no super compelling 
reason to spend time and resources on backporting JDK-8233506 at this 
time. However, backporting only JDK-8224675 would be a mistake, as it 
would destabilize ZGC (including the x86 port) so you would basically 
have to go all the way to JDK-8230565, or alternatively don't backport 
JDK-8224675 and adjust the aarch64 port accordingly.

Whatever path you take here, it would require significant work and 
testing, which is why I'd again recommend that you to consider using JDK 
14 (when it's GA) for these workloads.

cheers,
Per

On 1/16/20 4:01 AM, Yangfei (Felix) wrote:
> Hi,
> 
>> Hi,
>>
>> Please note that backporting JDK-8224675 "Late GC barrier insertion for ZGC"
>> is not great idea, since that patch introduced stability issues and the whole
>> approach was later superseded by JDK-8230565 "ZGC: Redesign C2 load
>> barrier to expand on the MachNode level".
>>
>> If you want to go down this path, I'd suggest that you either don't backport
>> JDK-8224675 at all, or backport everything up to JDK-8224675 + JDK-8230565.
>> Also note that if you include JDK-8230565 you want to be careful to also include
>> any followup bug fixes, like JDK-8233506.
> 
> Thanks for pointing this out.  It's helpful for our current work.
> We plan to start with the four patches and will check for other necessary ones.
> We noticed patches like JDK-8230565 are necessary for x86 zgc, but it's not there in jdk11.
> Users who want to stay with LTS versions like jdk11 will most likely come to the problems when they try zgc on the x86 platform.
> Is there a plan to incorporate these patches in jdk11?
> 
>> In general, a lot of stability and performance improvements have gone into ZGC
>> since JDK 11. If at all possible, I would strongly recommend using JDK 14
>> instead, where you already have aarch64 support and all other goodies.
> 
> Does that mean zgc in jdk11 will not be maintained by the community?
> 
> 
> Thanks,
> Felix
> 


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