You can look at your process' VmSize and VmRSS in /proc/<pid>/status.
You can also look at the number of page faults occuring in your process
(this is one of the values in /proc/<pid>/stat, but I don't remember which
one OTOMH). Your process will incur a minor fault when something else
causes one of its pages to be swapped out and a major fault when the
process needs to swap it back it).