socketbuffers

Socket buffers are memory regions used by a computer's networking stack to hold data that is being sent or received over a socket. They help decouple application I/O from network I/O and provide buffering that smooths differences in processing speeds between the application, the transport protocol, and the network.

On most systems there are separate buffers for the send path and the receive path. In Linux, the kernel uses data structures such as the socket’s send and receive queues composed of sk_buff objects; BSD and Windows use analogous buffering concepts (mbufs and NET_BUFFER_LIST, respectively). These buffers store the data, track its length, and maintain metadata such as timestamps, protocol headers, and pointers to data buffers or memory pages.

Data flows through socket buffers during normal operation. When an application writes to a socket, data is placed into the send buffer, possibly copied or referenced from user space, and the transport layer transmits it when able. Incoming data from the network is stored in the receive buffer until the application reads it. If buffers become full, the kernel can apply backpressure, blocking or signaling the application to slow down or adjust I/O behavior.

Buffer sizes influence performance and latency. Applications and systems configure buffer sizes with options such as SO_SNDBUF and SO_RCVBUF, and kernel tunables control overall memory usage for network buffers. Features such as zero-copy sending, batching, and efficient memory management reduce copies and improve throughput, but require careful tuning to balance memory usage with latency and throughput.

Effective management of socket buffers involves aligning buffer sizes with workload characteristics, monitoring memory pressure, and applying appropriate I/O modes (blocking or non-blocking) to achieve desired performance.