I was performing an activity wherein i had to calculate the total memory used by the system, and then give the accounting for the total used memory in terms of processes and other entities.

I used /proc/meminfo to get total used memory (Total Usable Mem - Total Free Mem).
Then listed out all the processes and there individual memory usage.
But both figures didnt match which was not what I expected to be. 
Even with the total memory used by all processes I was not able to get account for 7MB to used memory.

Am I missing any piece of information here ?