RFR (S): 8201490: Improve concurrent mark keep alive closure performance

[Kim Barrett]

> On Apr 13, 2018, at 4:18 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> http://cr.openjdk.java.net/~tschatzl/8201490/webrev.0_to_1 (diff)
> http://cr.openjdk.java.net/~tschatzl/8201490/webrev.1 (full)
> 
> Thanks,
>  Thomas

Looks good.