finding memory leaks in extensions

Hello, 

I'm trying to detect memory leaks in an external postgres extensions.
Since SIZE of postgres process keeps growing between function calls,
does this mean there are memory leaks in the extenal packages or
it might be the postgres itself keeping allocated memory as a buffer
for later use ? To note also that the same identical calls keeps
making SIZE grow ...

PS: I'm working with postgres-7.3.2

TIA
--strk;