RFR: More efficient next bitmap resetting for traversal

[Aleksey Shipilev]

On 07/16/2018 05:33 PM, Roman Kennke wrote:
> The resetting of next bitmap for traversal is a bit inefficient:
> - It's iterating *all* regions, but then only picks traversal-set
> regions. We can iterate traversal-set to begin with instead.
> - It grabs the heap-lock for each region. Which basically serializes the
> whole process for no good reason.
> 
> http://cr.openjdk.java.net/~rkennke/better-traversal-reset-bitmaps/webrev.00/

Looks good, except:

 *) You don't need this iterator now?

 511     ShenandoahHeapRegionSetIterator iter(traversal_set);

Thanks,
-Aleksey