[8u40] RFR: 8056240: Investigate increased GC remark time after class unloading changes in CRM Fuse

[Stefan Karlsson]

Hi all,

Please, review the backport of this fix to 8u40:
http://cr.openjdk.java.net/~stefank/backports/8u40/8056240/webrev.01/

I've attached the .rej files from applying the JDK 9 patch to JDK 8u40.

Reasons for the .rej files from the failed applied patch hunks:
  metadataOnStackMark.cpp - the has_redefined_a_class parameter in 
MetadataOnStackMark(bool has_redefined_a_class) is only present in JDK 9.
  metadataOnStackMark.hpp - the same as above
  classLoaderData.cpp - has_redefined_a_class parameter and JDK-8040237 
isn't backported
  concurrentMark.cpp - JDK-8027450 isn't backported

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