6.1 Registering / Unregistering Memory for RDMA

The interface provides functions to register(pin) and unregister(unpin) memory on the NIC hardware. The emulated version of these operations do not do anything.

int CmiRegisterMemory(void *addr, unsigned int size);
This function takes an allocated memory at starting address addr of length size and registers it with the hardware NIC, thus making this memory DMAable. This is also called pinning memory on the NIC hardware, making remote DMA operations on this memory possible. This directly calls the hardware driver function for registering the memory region and is usually an expensive operation, so should be used sparingly.

int CmiUnRegisterMemory(void *addr, unsigned int size);
This function unregisters the memory at starting address addr of length size, making it no longer DMAable. This operation corresponds to unpinning memory from the NIC hardware. This is also an expensive operation and should be sparingly used.

For certain machine layers which support a DMA, we support the function void *CmiDMAAlloc(int size);
This operation allocates a memory region of length size from the DMAable region on the NIC hardware. The memory region returned is pinned to the NIC hardware. This is an alternative to CmiRegisterMemory and is implemented only for hardwares that support this.