RFR: Add remaining unused free space to 'used' counter in free list

[Aleksey Shipilev]

On 12/13/2016 06:03 PM, Roman Kennke wrote:
> I noticed that when a program allocates many objects that are slightly
> larger than half a region, we would continuously run into full GC. The
> reason is that when we skip to next region for allocation, we did not
> count the remaining unused free space as 'used', and thus barely
> reported half of heap remaining when running OOM. Oops.
> 
> Fixed in ShenandoahFreeList by adding last-current-region's remaining
> free() to the free-lists used.
> 
> Ok?
> 
> http://cr.openjdk.java.net/~rkennke/fixused/webrev.00/

I don't see how it matches with the reverse operation, which decrements based on
region used size only, not its free size?

See:
       heap->decrease_used(region->used());
      _heap->decrease_used(r->used());

Thanks,
-Aleksey