how to find the physical memory allocated to the kernel

[Bharma Ji]

Hi
Is there any way to determine the physical memory(not the virtual address
space) being allocated to the kernel at any instant? The overall problem is
that once I allocate say 512 MB to the kernel (virutal address space)
through the config file at compile time, I want to figure out how much of
that space is actually being used when the machine is under load.
Thanks for any answers