kmalloc is the normal method of allocating memory in the kernel.
The flags argument may be one of:
GFP_USER - Allocate memory on behalf of user. May sleep.
GFP_KERNEL - Allocate normal kernel ram. May sleep.
GFP_ATOMIC - Allocation will not sleep. Use inside interrupt handlers.
Additionally, the GFP_DMA flag may be set to indicate the memory must be suitable for DMA. This can mean different things on different platforms. For example, on i386, it means that the memory must come from the first 16MB.