how to kill %SYSTEM.WorkMgr process

i use %SYSTEM.WorkMgr  to handle data by multicompile=1,but i find that,after WaitForComplete,the processes created by %SYSTEM.WorkMgr  are still stand by,

and status is evtw,after i run many times,the processes are more.and this will cause server falls into trouble.so my question is ，how to kill the processes that created by using the %SYSTEM.WorkMgr，and how to avoid  to make the server falls into trouble,why  this will cause server falls into trouble。and is there a better way to handle data by mult process？