The inner workings of TCP zero-copy
Hacker News
March 2, 2026
AI-Generated Deep Dive Summary
TCP zero-copy is a feature of the Linux kernel that eliminates unnecessary data copying between kernel memory and user space, significantly improving network performance for high-bandwidth applications. By directly referencing userspace buffers, it reduces overhead, making it particularly valuable for systems requiring efficient data transfer. This feature was introduced in 2017 with the MSG_ZEROCOPY flag in sendmsg(), allowing asynchronous sends without data duplication. However, its effectiveness depends on hardware support for scatter-gather DMA operations.
On the receive side, zero-copy is more complex due to the need for processing TCP headers while directing payload data directly to user space buffers. This requires memory registration and careful handling of kernel resources. The process involves the kernel generating headers in separate buffers while the payload is sent to the destination buffer, ensuring minimal copying and efficient use of system resources.
The introduction of io_uring in 2022 further enhanced zero-copy functionality by providing a streamlined asynchronous API for TCP transfers. This advancement simplifies the implementation of zero-copy operations, offering better performance and scalability compared to traditional methods. Developers can now leverage io_uring's send_zc() operation for efficient data transmission, with notifications ensuring proper buffer management.
For developers, understanding TCP zero-copy is crucial for optimizing high-performance networking applications. Its benefits include reduced latency, improved throughput, and lower CPU usage, making it essential for tech startups and enterprises aiming to maximize network efficiency. As modern applications demand faster and more reliable data transfers, mastering zero-copy techniques can provide a competitive edge in delivering scalable solutions.
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Originally published on Hacker News on 3/2/2026