Query on memory of a process

[arnab]

Hi All,
I have a basic doubt about a process memory consumption.
For a particular process when I do top -p (pid) I get the RSS size of
the process, which is nothing but the memory consumption of the
process.

Now when I do cat /proc/pid/statm
whose memory output never matches with the RSS size.What is the memory
returned by the statm file ?

Thanks in advance.
Regards
Arnab