What would be a good way to determine the current heap size (VSZ) for a process on Linux?

I always used sbrk(0) for that, which used to return the top of the heap. However recently, to my dismay, I discovered that it does not work on Linux -- I successfully malloc()-ed 1GB, could confirm it with "ps -o pid,vsz,args", and yet sbrk(0) always returns the same value as right in the beginning.

As a work around, I have to open /proc/<pid>/stat and read out the 23d field from there. However it is heavy and ugly, and I have a feeling that such a thing should be done in a more elegant way.

Please help. Any suggestions will be greatly appreciated. I even tried to play with mallinfo(), however could not figure out how to interpret results.

Thank you,