NAND Flash L2P Table Region Tracking via Bitmap Filtering
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Solution Overview
Problem
Traditional flash memory devices face inefficiencies in garbage collection due to the need to load and search large logical-to-physical (L2P) translation tables, leading to high latencies and increased processing time, especially when tables are larger than the working memory capacity.
Innovation Solution
Implementing a table region data structure that uses a bitmap to indicate relevant L2P table regions for a block, allowing only pertinent regions to be loaded into working memory, and filtering stale data by resetting indications when pages are rewritten or erased, thereby reducing the need for unnecessary searches during garbage collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the complete L2P translation table is loaded into working memory for garbage collection, then all logical page mappings can be searched, but the working memory capacity is exceeded and processing time increases
Solution Approach 1:
The L2P translation table is divided into multiple regions, and a bitmap data structure is used to indicate which regions contain valid mappings for a given physical block. During garbage collection, only the indicated regions are loaded into working memory and searched, rather than loading the entire table. This segmentation approach maintains search completeness while reducing memory usage and processing time.
2Reliability
If all L2P table regions are loaded into working memory, then no valid pages are missed, but the working memory requirement exceeds available capacity
Solution Approach 1:
The bitmap data structure extracts and identifies only the relevant L2P table regions that contain mappings for a specific physical block. By using the bitmap to indicate which regions to load, the system extracts only the necessary portions of the L2P table into working memory, maintaining valid page identification accuracy while reducing memory consumption to fit within available capacity.
3Device complexity
If the bitmap indications are not updated when pages are rewritten or erased, then the bitmap remains simple to maintain, but stale indications cause unnecessary searches and reduce garbage collection efficiency
Solution Approach 1:
The system implements feedback mechanisms where the bitmap is dynamically updated when logical pages are rewritten or erased. When a page rewrite or erase operation occurs, the corresponding bitmap indication is cleared to reflect that the mapping is no longer valid. This feedback ensures the bitmap remains accurate, preventing stale indications from causing unnecessary searches, while maintaining garbage collection efficiency.
Data Source
AI summary
Devices and techniques for synchronizing NAND logical-to-physical table region tracking are described herein. Table region data structures for physical blocks are maintained. These structures include logical-to-physical (L2P) mapping table portions that point to the respective physical blocks. When garbage collection is performed on a block, table region structures for that block, and another (e.g., the next block to be garbage collected) are read to avoid loading L2P table regions that do not point to the block. If any of the read portions of the L2P table region fail to point to either the block or the other block, these L2P table portions are removed from the loaded table region data structures.