RFR(s): 8145312: CMS: There is insufficient memory with CMSSamplingGrain=1

[sangheon]

Hi all,

Could I have some reviews for CMSSamplingGrain flag?

The flag is used to calculate points at which the young gen should be 
partitioned for doing parallel work, so it only makes sense to partition 
at a granularity equal to or larger than the object size.

I am proposing to change the minimum value of CMSSamplingGrain from '1' 
to 'ObjectAlignmentInBytes'.  (ObjectAlignmentInBytes has a range of [8, 
256]).

In addition, I added a constraint function to avoid an arithmetic 
overflow by its maximum value.

CR: https://bugs.openjdk.java.net/browse/JDK-8145312
Webrev: http://cr.openjdk.java.net/~sangheki/8145312/webrev.00/
Testing: JPRT, RBT for all platforms including embedded

Thanks,
Sangheon