A client sends 1 KB TCP packets every second with a 4 KB SO_SNDBUF while the server never calls recv(), yet the observed Send‑Q grows to 14 480 bytes, revealing how the Linux kernel doubles the buffer size, uses sk_wmem_queued, and expands write queues via GSO and memory scheduling.
A Linux client that sets SO_SNDBUF to 4096 bytes and sends 1 KB packets to a non‑receiving server sees the TCP Send‑Q grow to 14480 bytes, revealing how the kernel doubles the buffer size, uses sk_wmem_queued, and expands memory via GSO‑driven size goals.
This article explains why a TCP connection's Send‑Q can exceed the user‑set SO_SNDBUF value, detailing the kernel's double‑buffer trick, sk_wmem_queued accounting, tcp_sendmsg behavior, GSO influence, and possible ways to limit the buffer growth.
A Linux client sets SO_SNDBUF to 4096 bytes, sends 1 KB packets while the server never reads, yet the TCP Send‑Q grows to 14480 bytes because the kernel doubles the buffer size, adds overhead, and expands memory via GSO and sk_wmem scheduling.
This article explains why the TCP Send‑Q can grow beyond the user‑set SO_SNDBUF value by examining the kernel’s double‑buffer accounting, sk_wmem_queued handling, and the interaction of tcp_sendmsg with GSO, supported by code excerpts and diagrams.
