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

[Stefan Karlsson]

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