GPUDirect and RDMA
Every transfer that has to bounce through a staging buffer in host memory pays for it twice — once copying into the buffer, once out — and that cost shows up whenever a GPU needs to talk to something other than another GPU on the same NVLink fabric: a network card, an NVMe drive, storage over the network. GPUDirect is NVIDIA's umbrella name for the mechanisms that let those other devices address GPU memory directly instead.