umem

UMEM is an acronym used in information technology with multiple meanings depending on context. In networking software, UMEM most commonly denotes a memory region used by user-space packet processing to exchange data with the kernel without extra copying. The Linux AF_XDP framework uses UMEM as a shared memory pool that holds the actual packet payloads. Applications allocate and map an UMEM region, decide frame size and number of frames, and then populate ring buffers for transmitting and receiving packets. The kernel and user-space threads access the same UMEM region, enabling zero-copy packet paths and lower latency.

Within AF_XDP, the typical arrangement includes an UMEM buffer pool presented to user space as memory, plus several rings: a fill queue to supply free frames, a completion queue to release transmitted frames, and separate RX/TX rings for packet descriptors. Managing UMEM efficiently involves aligning frame sizes to hardware constraints, handling memory fragmentation, and ensuring synchronization between kernel and user space.

Other uses of the term UMEM appear in general software documentation as short for “user memory” or, in certain GPU or computing contexts, as a reference to memory managed by software rather than devices. In these cases, UMEM is not a formal standard and definitions vary by project.

See also: XDP, AF_XDP, zero-copy, DMA, memory management, packet processing.