nearzerocopy

Near-zero-copy is a set of techniques aimed at reducing the amount of data copying between memory regions or software layers in input/output paths, especially between user space and kernel space or between different subsystems. The objective is to lower CPU overhead and memory bandwidth usage while maintaining data integrity and correctness.

Key techniques associated with near-zero-copy include memory mapping (mmap) to share buffers between components, and scatter/gather I/O (readv/writev) to assemble or disassemble data without duplicating it in user space. Other common methods are zero-copy APIs such as sendfile and splice, which transfer data within the kernel or between devices with minimal or no user-space copies. Memory pinning or direct I/O can keep buffers resident in RAM, and DMA-capable hardware or kernel-bypass frameworks can further reduce copying by moving data directly between devices and memory. In software, using pre-allocated, reusable buffers and producer-consumer ring buffers helps avoid repeated allocations and copies.

Typical use cases include high-performance networking servers, real-time streaming, large-scale data processing pipelines, and IPC in multi-process environments. Benefits include lower CPU utilization, higher throughput, and reduced latency, especially on systems with fast storage or network hardware.

Trade-offs and considerations include increased complexity, reduced portability across platforms, and careful memory management to avoid leaks or premature deallocation. Some unavoidable copies may remain due to data formatting, synchronization, or safety checks. Near-zero-copy is thus a practical compromise: it aims for near-zero overhead in common paths while acknowledging that exact zero-copy is not always achievable everywhere. Technologies and libraries in this space include user-space networking stacks, direct buffers, DMA-enabled I/O, and kernel-bypass I/O frameworks.