Rearchitecting Buffered I/O in the Era of High-Bandwidth SSDs

Buffered I/O via page cache has been prevalently used by applications for decades due to its user-friendliness and high performance. However, the existing buffered I/O architecture fails to effectively utilize high-bandwidth Solid-State Drives (SSDs) caused by 1) costly page caching overused for buffering all incoming writes in the critical path, 2) the limited concurrency of page management, and 3) the high read-before-write penalty for partial-page writes.

This paper rearchitects buffered I/O and proposes a write-scrap buffering approach (WSBuffer) to remove the aforementioned shackles of buffered I/O on writes to proactively exploit fast SSDs while retaining all the advantages of buffered I/O on reads. WSBuffer first presents a novel memory-page buffering structure, scrap buffer, to efficiently buffer SSD-I/O unfriendly writes and expensive partial-page writes. WSBuffer further proposes a buffer-minimized data access mechanism to partially buffer small and unaligned parts of user writes via the scrap buffer while directly sending large and aligned parts to underlying SSDs. Finally, WSBuffer devises an opportunistic two-stage dirty-data flushing mechanism and a concurrent page management mechanism to achieve fluent and fast dirty-data flushing. The experimental results show that WSBuffer outperforms Linux file systems of EXT4, F2FS, BTRFS and XFS, as well as the state-of-the-art buffered I/O optimization of ScaleCache by up to 3.91X and 82.80X in throughput and latency respectively.