RFR: Protect more internal code from false sharing

[Aleksey Shipilev]

On 10/22/2018 09:14 PM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/paddings/webrev.01/
> 
> This makes more internal code resilient to false sharing. I have inspected all (?) places where we
> do multi-threaded access to contended data, and put the paddings around them. There is the
> ShenandoahSharedCounter abstraction in work, but it requires quite a bit more attention to get right.
> 
> This seems to improve final-mark performance on SPECjbb due to code root scanning improvements. I'll
> run a few other benchmarks too overnight.

Other benchmarks are largely unaffected.

-Aleksey