Where is the linux mem gone?

#/bin/bash for PROC in `ls /proc/|grep "^[0-9]"` do if [ -f /proc/$PROC/statm ]; then TEP=`cat /proc/$PROC/statm | awk '{print ($2)}'` RSS=`expr $RSS + $TEP` fi done RSS=`expr $RSS \* 4` PageTable=`grep PageTables /proc/meminfo | awk '{print $2}'` SlabInfo=`cat /proc/slabinfo |awk 'BEGIN{sum=0;}{sum=sum+$3*$4;}END{print sum/1024/1024}'`

echo $RSS"KB", $PageTable"KB", $SlabInfo"MB" printf "rss+pagetable+slabinfo=%sMB\n" `echo $RSS/1024 + $PageTable/1024 + $SlabInfo|bc` free -m

I use the shell sum my mem is shows

rss+pagetable+slabinfo=19422.716MB

and use free -m total used free shared buff/cache available Mem: 64150 60728 1955 61 1465 2866 Swap: 16383 3490 12893

It shows mem used 60728m where is the other mem gone? somebody konws ? thanks