RFR (S): 8037344: Use the "next" field to iterate over fine remembered instead of using the hash table

[Thomas Schatzl]

Hi all,

  I have been notified that the webrev does not apply to the jdk9/hs-gc
repository any more.

Here is an updated version:
http://cr.openjdk.java.net/~tschatzl/8037344/webrev.1/

On Fri, 2014-03-14 at 17:41 +0100, Thomas Schatzl wrote:
> Hi all,
> 
>   could I have reviews for this small change that cleans up the
> HeapRegionRemSet-iterator?
> 
> The reason for this change is that in JDK-7182260 linked together all
> PerRegionTable data structure (representing parts of the fine remembered
> set) of a fine remembered set for a particular region. However the iterator still walks the hash table.
> 
> I took the opportunity to try to slightly improve the documentation of
> the HeapRegionRemSetIterator (comments) as the change changes the
> HeapRegionRemSetIterator interface already anyway.
> 
> A micro-benchmark that does nothing for every card indicates that
> iterating of the PRTs got a lot faster (mainly due to the less
> complicated check in HeapRegionRemSetIterator::fine_has_next() I assume) and is only a side-effect of the change.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8037344
> 
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8037344/webrev/
> 
> Testing:
> jprt, specjbb*, specjvm2008*, dacapo and other benchmarks having large
> remembered sets.
> 

Thanks,
  Thomas