The chunk created by mslab may cause memory fragement and lead to fullgc

The default size of chunk is 2m, when we use G1, if heapRegionSize equals 4m, these chunks are allocated as humongous objects, exclusively allocating one region, then the remaining 2m become memory fragement.

Lots of memory fragement may lead to fullgc even if the percent of used heap not high enough.

I have tested to reduce the chunk size to 2047k(2m-1k, a bit lesser than half of heapRegionSize), there was no repeat of the above.

BTW, in G1, humongous objects are objects larger or equal the size of half a region, and the heapRegionSize is automatically calculated based on the heap size parameter if not explicitly specified.