Many journaling file systems currently use non-volatile memory-express (NVMe) solid-state drives (SSDs) as external journal devices to improve the input and output (I/O) performance. However, when facing microwrite workloads, which are typical of many applications, they suffer from severe I/O fluctuations and the NVMe SSD utilization is extremely low. The experimental results indicate that this phenomenon arises mainly because writing back data to backend file systems on hard disk drives is much slower than journal writing, causing journal writing to frequently freeze because of the two-phase mechanism. We, therefore, propose a merging-in-memory (MIM) acceleration architecture to stabilize and boost the I/O performance for such journaling file systems. MIM employs an efficient data structure of hash-table-based multiple linked lists in memory, which not only merges random microwrites into sequential large blocks to speed up writebacks but also provides additional gains in terms of reducing the frequency of write addressing and object opening and closing. Using a prototype implementation in Ceph FileStore, we experimentally show that MIM not only eliminates severe fluctuations but also improves the I/O operations per second by roughly 1×–12× and reduces the write latency by 75%–98%.

当前，许多日记文件系统都使用非易失性内存表达（NVMe）固态驱动器（SSD）作为外部日记设备，以提高输入和输出（I / O）性能。但是，当面对许多应用程序中常见的微写工作负载时，它们会遭受严重的I / O波动，并且NVMe SSD利用率极低。实验结果表明，出现这种现象的主要原因是，将数据写回到硬盘驱动器上的后端文件系统比日记写慢得多，由于两阶段机制，导致日记写频繁冻结。因此，我们提出了一种内存合并（MIM）加速体系结构，以稳定和提高此类日记文件系统的I / O性能。MIM在内存中采用了基于哈希表的多个链表的高效数据结构，它不仅可以将随机微写合并到连续的大块中，以加快写回速度，而且还可以减少写寻址和对象打开和关闭的频率，从而提供额外的收益。通过使用Ceph FileStore中的原型实现，我们通过实验证明MIM不仅消除了严重的波动，而且还将每秒的I / O操作提高了大约1×–12×，并减少了75％–98％的写入延迟。