L2P Table Caching for Asynchronous Power Loss Recovery
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Solution Overview
Problem
Existing memory sub-systems face challenges in asynchronous power loss recovery, particularly when the logical-to-physical (L2P) table is partially cached, leading to high recovery times and write amplification rates due to inadequate strategies for managing cache misses and journaling operations.
Innovation Solution
Implementing an L2P dumping strategy based on a combination of data page write count and L2P table cache miss count, using a weighted sum to determine the dump rate, which balances recovery times and write amplification rates by maintaining counters for page writes and cache misses and dumping cached regions accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the L2P table is partially cached in volatile memory, then access speed is improved, but recovery time increases after power loss
Solution Approach 1:
The patent implements preliminary action by maintaining a journal of L2P table updates in non-volatile memory before power loss occurs. This journal contains incremental changes that can be rapidly applied during recovery, eliminating the need to reconstruct the entire L2P table from scratch. The journaling mechanism prepares the system in advance for potential power failures, enabling fast recovery by simply replaying the journal entries.
Solution Approach 2:
The patent uses copying by maintaining a volatile memory cache as a copy of the L2P table for fast access, while the authoritative version resides in non-volatile memory. During normal operation, the volatile cache provides rapid access. Upon power loss, the system recovers by replaying journals and reconstructing the cache copy, combining the speed benefits of volatile memory with the persistence of non-volatile storage.
2Productivity
If the L2P table is partially cached, then access performance is improved, but write amplification rate increases
Solution Approach 1:
The patent extracts the journaling function from the main L2P table update path. Instead of writing every L2P update directly to non-volatile memory, the system extracts incremental changes into a separate journal structure. This allows the main L2P table to be updated in the volatile cache without immediately persisting to storage, reducing write amplification while maintaining data integrity through the journal.
Solution Approach 2:
The patent implements discarding and recovering by allowing the volatile L2P cache to be discarded (lost) upon power failure, while the essential update information is preserved in the non-volatile journal. During recovery, the system recovers the L2P table by replaying the journal, efficiently reconstructing only the necessary data without requiring protective writes of the entire cache contents.
Data Source
AI summary
An example memory sub-system includes a memory device and a processing device, operatively coupled to the memory device. The processing device is configured to maintain a logical-to-physical (L2P) table, wherein a region of the L2P table is cached in a volatile memory; maintain a write count reflecting a number of bytes written to the memory device; maintain a cache miss count reflecting a number of cache misses with respect to a cache of the L2P table; responsive to determining that a value of a predetermined function of the write count and the cache miss count exceeds a threshold value, copy the region of the L2P table to a non-volatile memory.