I encountered a strange problem。
When I used "free -m" show the memory use status,It's show have used 7GB memory,but use "ps -aux" show just used 4GB memory.
As you know ,when I used "free -m" show the memory status,I had Minus "buffers" and "cached",caculated the used memory.
So I don't know remain 3GB memory is used by which program.