垃圾收集比较

	YoungGC/MinorGc	OldGC/MajorGC
Serial	{STW} copy	{STW}mark&compact
Parallel Scavenge	{STW} copy	{STW}mark&compact
CMS		{STW}initMark => {Conc}Mark =>{STW}FinishMark=>{Conc}Sweep
G1		{STW}initMark=>{Conc}Mark=>
ZGC