spark structured stream with kafka don't really delete temp files in spark standalone cluster

the folder in  Driver

/tmp/temporary-xxxxxxxx

 takes up all the space in /tmp after runing spark structured stream job a long time.

it is mainly under the offsets and commits folders.but when I watch it by us command

du -sh offsets     du -sh commits

it got more than 600M,but when We  use command

ll -h offsets       ll -h commits

it got 400K.

I think it is because when the file is deleted,it is still used in job.

It wasn't released only if the job is stopped.

How can I solve it?

We use 

df.writeStream.trigger(ProcessingTime("1 seconds"))

not

df.writeStream.trigger(Continuous("1 seconds"))

Is there something wrong here?