RFR (XXS): 8133456: HeapRegionManager::shrink_by() iterates suboptimally across regions

[Bengt Rutisson]

Hi Thomas,

On 2015-08-21 10:05, Thomas Schatzl wrote:
> Hi all,
>
>    can I have reviews for this one-line change that improves efficiency
> during heap shrinking?
>
> The problem was that the increment to skip over already scanned regions
> has been too conservative. In some cases it would mean that regions in
> the region table would be scanned twice.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8133456
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8133456/webrev/

The fix looks good, but do we really need both cur and idx_last_found? 
After your fix we just set them to the same value. Technically it would 
be enough that find_empty_from_idx_reverse() takes one parameter that is 
both the in and out value. But it may be cleaner to have the two separated.

I'll leave it up to you if you want to change it. I'm fine with the 
proposed patch too.

Thanks,
Bengt

> Testing:
> jprt, vm.gc
>
> Thanks,
>    Thomas
>