dm_mod module

Hi, I recently compiled my own kernel to enable ACPI suspend to RAM (which is working great now btw). The kernel version I used was 2.6.8.1. Now. when I boot I get a message saying device mapper could not be started and that module dm_mod could not be loaded. I tried to figure out what options I must enable in the .config file to compile dm_mod module but could not figure it out. Can someone help me? How serious is this error? and, what am I missing because of lack of device mapper? thanks, Osho