一句话：提出 BypassD，一种利用虚拟地址与 IOMMU 硬件翻译、让应用无需修改即可快速用户态访问共享 SSD 的 I/O 架构。
现代 NVMe SSD（如 Optane）提供微秒级延迟和数 GB/s 带宽，使内核 I/O 栈成为显著开销。现有用户态方案虽绕过内核，却难以在不大改文件系统、OS 或硬件的前提下支持共享存储。BypassD 借鉴虚拟内存：内核为文件内容在页表中建立映射，用户态 I/O 请求用虚拟地址指定文件与偏移；并通过扩展 IOMMU 将文件偏移翻译为设备逻辑块地址，同时提供硬件保护。应用无需修改即可使用。评估显示，相比标准 Linux 内核，BypassD 将 4KB 访问延迟降低 42%，性能接近不支持设备共享的 SPDK；消除软件开销后，WiredTiger 存储引擎等真实负载性能提升约 20%。
Modern storage devices, such as Optane NVMe SSDs, offer ultra-low latency of a few microseconds and high bandwidth of multiple gigabytes per second. At these speeds, the kernel software I/O stack is a substantial source of overhead. Userspace approaches avoid kernel software overheads but face challenges in supporting shared storage without major changes to file systems, the OS or the hardware. We propose a new I/O architecture, BypassD, for fast, userspace access to shared storage devices. BypassD takes inspiration from virtual memory: it uses virtual addresses to access a device and relies on hardware for translation and protection. Like memory-mapping a file, the OS kernel constructs a mapping for file contents in the page table. Userspace I/O requests then use virtual addresses from these mappings to specify which file and file offset to access. BypassD extends the IOMMU hardware to translate file offsets into device Logical Block Addresses. Existing applications require no modifications to use BypassD. Our evaluation shows that BypassD reduces latency for 4KB accesses by 42% compared to standard Linux kernel and performs close to userspace techniques like SPDK that do not support device sharing. By eliminating software overheads, BypassD improves performance of real workloads, such as the WiredTiger storage engine, by ~20%.
@inproceedings{YadalamAKGS24,
title = {BypassD: Enabling fast userspace access to shared SSDs},
author = {Sujay Yadalam and Chloe Alverti and Vasileios Karakostas and Jayneel Gandhi and Michael Swift},
booktitle = {ASPLOS},
year = {2024},
doi = {10.1145/3617232.3624854}
}