collectgarbage (opt [, arg]) 
This function is a generic interface to the garbage collector. 
It performs different functions according to its first argument, opt: 


"stop": stops the garbage collector.  禁用垃圾收集器 

"restart": restarts the garbage collector. 重启垃圾收集器

"collect": performs a full garbage-collection cycle. 完全垃圾收集

"count": returns the total memory in use by Lua (in Kbytes). 查询内存占用(Kb)

"step": performs a garbage-collection step. 

The step "size" is controlled by arg 
(larger values mean more steps) in a non-specified way. 
If you want to control the step size you 
must experimentally tune the value of arg. 
Returns true if the step finished a collection cycle. 

"setpause": sets arg/100 as the new value for the pause of the collector.  垃圾收集中断量

"setstepmul": sets arg/100 as the new value for the step multiplier of the collector. 垃圾收集工作量