Although RTAI is designed to run in processors with MMU, all the application tasks and the RTAI kernel run in the same address space. There is no memory protection between tasks and the RTAI kernel and also between threads themselves.
From the point of view of memory management, RTAI is the guest operating system of the Linux Kernel. The Linux kernel has the whole control of the memory.
The module rt_mem_mgr provides the functions rt_malloc() rt_free().
Some amount of memory is pre-allocated then the module in inserted, and real time tasks can allocate and free memory from this pool while executing in RTAI environment.