RFR(S): 8011724: G1: Stack allocate instances of HeapRegionRemSetIterator

[Bengt Rutisson]

Hi John,

Thanks for doing this cleanup! It really looks much better!

Changes look good.

One minor request if you feel like it:

Since you anyway updated a comment in the class 
HeapRegionRemSetIterator. Could you also update (or just remove) this 
comment?

   // If true we're iterating over the coarse table; if false the fine
   // table.
   enum IterState {
     Sparse,
     Fine,
     Coarse
   };

Also, have you measured any performance impact of this? I'm not 
suggesting that you should put any extra work into doing that. Just, in 
case you have some numbers, have you seen any improvements? I could 
imagine that there was a fair amount of false sharing going on with the 
old array of iterators, so I'm guess that we might see some perf 
improvements with this change. Just curious.

Thanks,
Bengt

On 4/8/13 8:49 PM, John Cuthbertson wrote:
> Hi Everyone,
>
> Can I have a couple of reviews of these changes: 
> http://cr.openjdk.java.net/~johnc/8011724/webrev.0 ?
>
> Summary:
> I've changed RSet scanning to stack allocate instances of the 
> HeapRegionRemSet iterator and removed the pre-allocated instances 
> (created during heap initialization).
>
> Testing:
> GC test suite with MaxTenuringThreshold=0, IHOP=1, and VerifyAfterGC 
> to create a lot of old data.; jprt.
>
> Thanks,
>
> JohnC