Improving AppCDS for Custom Loaders

[Volker Simonis]

yumin qi <yumin.qi at gmail.com> schrieb am Do. 10. Mai 2018 um 22:20:

> Hi, Jiangli
>
>   Thanks for the info.
>
> On Thu, May 10, 2018 at 11:39 AM, Jiangli Zhou <jiangli.zhou at oracle.com>
> wrote:
>
>> Hi Yumin and Volker,
>>
>> I’ve create an umbrella RFE JDK-8202854 to keep track this effort. New
>> sub-RFEs will be created and targeted for specific JDK releases when each
>> sub-item matures. Please refer to JDK-8202854 for future progress.
>>
>> Yumin, please see below for comments/questions.
>>
>> > Agree not including objects in java heap at now --- thanks Jiangli for
>> answering my question in other thread.
>>
> I conclude from above that you are not using java heap object archiving
>> due to different GC algorithm being used(?).  I would like to understand
>> more about your GC choices. Could you please provide more information on
>> that? G1 GC is the default GC in JDK. Thanks to our GC team, the
>> performance of G1 has been consistently improving over the recent JDK
>> releases, especially in JDK 9 and 10. I strongly encourage you to do
>> performance measurement/comparison and reevaluate your GC choice if G1 is
>> not used.
>>
>
> Most of our applications still using CMS, we  are pushing to switch to
> G1GC at this time but still most of them still with CMS. I know CMS will be
> removed so it will not be your focus.
>
>>
>> >   I think for #1, it does not conflict with the two layer archive
>> solution. We can skip the classes from base CDS archive, only dump the
>> non-base loaded classes into second archive, this gives one more option for
>> user to choose. Also it will be good after dump archive to let the
>> application continue to run.
>> >
>> >   Can we do a Full GC before dump at exit? it may unload not referenced
>> classes, or it is not necessary since CDS wants to resolve the startup
>> performance for all loaded classes?
>>
>> For classes loaded by the builtin loaders, they can be kept alive when
>> archiving phase start. For classes loaded by user defined class loaders, we
>> also need to prevent them from being unloaded before archiving. I have a
>> preliminary idea for how to do that. I can share more information on that
>> when it matures.
>>
>>
> Yes, if classes with custom class loader cleaned, the class loader itself
> will be purged. Full GC before exit may not be a good idea, but we can skip
> unloading classes --- in case dump objects in java heap.
>
>
Why not dump the classes iteratively, while they are loaded. Class loading
time would be the most natural time for dumping a class, and it‘s the time
when we know the most about a class (i.e. full class bytes).


> Thanks
> Yumin
>
>>
>>