As far as I know, there isn't any memory footprint profiling in Xdebug, I think there was at some point but they removed it because it was a little flaky. I like to monitor the memory usage within my scripts, and I've found this simple snippet can help.

The script defines a log_memory function that pushes the memory and time information into a session value. The register_tick_function method is used to add log_memory to the handler and its called over and over from inside his for loop.

You've probably never used it, never saw it, or never found a practical use for ticks, a underused and powerful feature of PHP that allows you to implement exceptions in PHP4, do intensive debugging and profiling, check database connections, turn PHP into an event driven language, or harness complex control over your code.

The post talks about what ticks are, how to enable them, and a few examples of how to use them. Check out more about them in this page on the PHP Manual.