RFR(XS): 8232533: G1 uses only a single thread for pretouching the java heap

[sangheon.kim at oracle.com]

Hi all,

Can I have some reviews for this small patch?

G1 initiates only 1 GC thread for faster start-up and then initialize 
more when we need more GC threads.
This is also same when we enable +AlwaysPreTouch option, so 1 thread 
touching all heap situation happens as the CR described.

The proposed patch is trying to cap the total worker thread count 
instead of active worker thread count. And this will make faster 
start-up as well.

CR: https://bugs.openjdk.java.net/browse/JDK-8232533
Webrev: http://cr.openjdk.java.net/~sangheki/8232533/webrev.0/
Testing: hs-tier1

Thanks,
Sangheon