A ring buffer is a fixed-length data structure where the first element follows the last. In computer vision, such buffers are used to store sequences of matrices for recurrent neural networks. Standard implementations using lists or flat arrays often require expensive memory reallocation or redundant data copying to maintain sequence order.
The 'magic ring buffer' technique leverages virtual memory to avoid these overheads. By mapping two adjacent virtual memory blocks to the same physical memory, the system ensures that any write to the first block is automatically reflected in the second. This allows the buffer to wrap around without modular arithmetic or data movement.
This approach requires the buffer size to be a multiple of the system's memory page size, typically 4KB on x86-64 architectures. Because manual virtual memory management is platform-specific, developers must implement separate solutions for Linux and Windows to handle memory mapping and file-backed sections.
On Linux, the implementation uses memfd_create to generate an anonymous file and mmap to map two virtual blocks to the same physical space. Windows requires a similar process using pagefile-backed sections, VirtualAlloc2, and MapViewOfFile3 to manage memory placeholders and ensure correct address alignment.
