RFR: 8056240: Investigate increased GC remark time after class unloading changes in CRM Fuse

[Mikael Gerdin]

Stefan,

On 2014-10-14 16:42, Stefan Karlsson wrote:
> Hi,
>
> Here are the latest changes based on comments from Bertrand and Mikael:
> http://cr.openjdk.java.net/~stefank/8056240/webrev.02
> http://cr.openjdk.java.net/~stefank/8056240/webrev.02.delta

Looks good to me.
/Mikael

>
> thanks,
> StefanK
>
> On 2014-10-13 15:11, Stefan Karlsson wrote:
>> Hi again,
>>
>> Latest changes after comments from Bertrand and Coleen:
>> http://cr.openjdk.java.net/~stefank/8056240/webrev.01
>> http://cr.openjdk.java.net/~stefank/8056240/webrev.01.delta
>>
>> 1) Updated AccessFlags:set_on_stack to use a looping cmpxchg
>> implementation.
>> 2) Remove MetadataOnStackMark::_doit and restructure
>> ClassLoaderDataGraph::do_unloading instead.
>> 3) Move MetadataOnStackBuffer and make it a utility class named
>> ChunkedList.
>>
>> thanks,
>> StefanK
>>
>> On 2014-10-02 12:53, Stefan Karlsson wrote:
>>> Hi all,
>>>
>>> (The following patch changes HotSpot code in areas concerning GC, RT,
>>> and Compiler. So, it would be good to get reviews from all three teams.)
>>>
>>> Please, review this patch to optimize and parallelize the CodeCache
>>> part of MetadaOnStackMark.
>>>
>>> G1 performance measurements showed longer than expected remark times
>>> on an application using a lot of nmethods and Metadata. The cause for
>>> this performance regression was the call to
>>> CodeCache::alive_nmethods_do(nmethod::mark_on_stack); in
>>> MetadataOnStackMark. This code path is only taken when class
>>> redefinition is used. Class redefinition is typically used in
>>> monitoring and diagnostic frameworks.
>>>
>>> With this patch we now:
>>> 1) Filter out duplicate Metadata* entries instead of storing a
>>> Metadata* per visited metadata reference.
>>> 2) Collect the set of Metadata* entries in parallel. The code
>>> piggy-backs on the parallel CodeCache cleaning task.
>>>
>>> http://cr.openjdk.java.net/~stefank/8056240/webrev.00/
>>> https://bugs.openjdk.java.net/browse/JDK-8056240
>>>
>>> Functional testing:
>>> JPRT, Kitchensink, parallel_class_unloading, unit tests
>>>
>>> Performance testing:
>>> CRM Fuse - where the regression was found
>>>
>>> The patch changes HotSpot code in areas concerning GC, RT, Compiler,
>>> and Serviceability. It would be good to get some reviews from the
>>> other teams, and not only from the GC team.
>>>
>>> thanks,
>>> StefanK
>>
>