Study of Effective Valid Page Tracking Methods in Mobile Flash Storage without DRAM

Jaesun No, Jinkyu Jeong

http://doi.org/10.5626/JOK.2025.52.5.357

Mobile systems, commonly use flash-based storage devices like Universal Flash Storage (UFS). These devices are designed with a small form factor and operate under limited power and budget constraints, often lacking large internal DRAM. As a result, they rely on small SRAM to run the Flash Translation Layer (FTL). This limitation makes it difficult to manage metadata, such as address mapping tables and the Valid Page Bitmap related to garbage collection (GC), within SRAM. Managing the Valid Page Bitmap in flash memory poses challenges due to performance degradation from significant metadata I/O overhead. This paper proposes an efficient method for tracking valid pages within specific blocks by managing L2P segment bitmaps per block. This approach minimizes the metadata access overhead during valid page tracking, leading to improved performance. Evaluation results indicate up to an 83% reduction in latency for finding valid pages compared to existing methods, particularly with a 128KB I/O unit.