Running 32 bit app on a 64 bit Linux machine Are there any performance drawbacks (CPU, Memory or IO) when running a 32-bit application on a 64-bit Linux? My main concern is inefficient utilization of pointers and memory blocks.

Practically no.

Note though that 64 and 32 bit application don't share libraries, so running one instance of 32 bit application may cause loading of many shared libraries "again".