How Much Memory Does a TCP Connection Really Use? Seven-Day Experiment Reveals Surprising Results

Experiment 1: ESTABLISH (Idle) Connections

The author created a large number of TCP sockets that remain in the ESTABLISH state without transmitting data, then recorded the kernel memory consumption. The results are shown in the following screenshots.

Experiment 2: Client → Server Data Transfer

In this test the client continuously sends data to the server while the kernel memory usage is monitored. Screenshots capture the memory growth and reclamation patterns.

Experiment 3: Server → Client Data Transfer

This scenario mirrors Experiment 2 but with the server sending data to the client. The captured images illustrate how the kernel allocates and frees buffers on the sending side.

Experiment 4: Non‑ESTABLISH States (e.g., TIME_WAIT)

The final set of tests examines sockets in states other than ESTABLISH, such as TIME_WAIT, to see how the kernel reclaims memory for these objects.

Summary of Findings

The collected data reveal several kernel‑level optimizations for socket memory usage:

The kernel promptly reclaims send and receive buffers; newer kernel versions perform this reclamation more aggressively.

The actual minimum size of send/receive buffers can be smaller than the configured rmem_min parameter.

In states such as TIME_WAIT, the kernel also frees auxiliary objects like socket_alloc that are no longer needed.

These mechanisms together reduce the per‑connection memory overhead, especially under high‑concurrency workloads.