Nonvolatile Memory Garbage Collection for Write Amplification Balance
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Solution Overview
Problem
Existing memory systems face issues with write amplification leading to shortened lifetime due to excessive or insufficient garbage collection operations, affecting performance and resource utilization in nonvolatile memory systems.
Innovation Solution
A memory system and control method that dynamically adjusts a write amplification threshold based on the number of active blocks, selectively identifying blocks with low valid data ratios for garbage collection, and optimizing data storage between SLC and TLC modes to balance resource utilization and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the frequency of garbage collection operation is increased to maintain more free blocks, then the availability of free blocks is improved, but the write amplification increases and lifetime is shortened
Solution Approach 1:
The patent implements dynamic adjustment of the garbage collection threshold based on the current number of free blocks. When free blocks fall below the threshold, garbage collection is triggered to restore free block availability. This dynamic mechanism adapts to changing system conditions, ensuring free blocks are maintained without excessive garbage collection operations that would increase write amplification.
Solution Approach 2:
The system changes the operational parameter (threshold for triggering garbage collection) based on the current state of the memory system. By adjusting when garbage collection is initiated based on the number of free blocks, the system optimizes the balance between maintaining free block availability and minimizing unnecessary write operations that contribute to write amplification.
2Duration of action of stationary object
If the frequency of garbage collection operation is decreased to reduce write amplification, then the lifetime is extended, but the number of free blocks becomes insufficient and performance deteriorates
Solution Approach 1:
The patent employs a dynamic threshold mechanism that adjusts the trigger point for garbage collection based on the current number of free blocks. This ensures garbage collection is performed only when necessary, avoiding both excessive operations that shorten lifetime and insufficient operations that degrade performance. The dynamic adaptation optimizes the balance between extending lifetime and maintaining productivity.
Solution Approach 2:
The system continuously monitors the number of free blocks and uses this feedback to determine when to initiate garbage collection. This feedback mechanism ensures that garbage collection is triggered only when free blocks fall below the threshold, preventing both over-collection (which would harm lifetime) and under-collection (which would harm performance).
3Quantity of substance
If blocks with high valid data ratio are selected for garbage collection, then the number of free blocks is restored, but the write amplification increases due to copying large amounts of valid data
Solution Approach 1:
The patent changes the selection criterion parameter from simply identifying any active block to specifically identifying blocks with valid data ratio below the threshold. This parameter change ensures that only blocks where garbage collection is beneficial (i.e., where not much valid data needs to be copied) are selected, thereby restoring free blocks while minimizing write amplification from data copying.
Solution Approach 2:
The system applies different selection criteria to different blocks based on their individual valid data ratios. Instead of uniformly selecting blocks for garbage collection, the system identifies specific blocks where the valid data ratio is below the threshold, making the garbage collection operation locally optimal for each selected block and minimizing unnecessary data copying.
4Loss of energy
If blocks with low valid data ratio are selected for garbage collection, then the write amplification is reduced, but the number of free blocks restored is insufficient
Solution Approach 1:
The patent implements a dynamic threshold mechanism that adapts to system conditions. When the number of free blocks falls below the threshold, garbage collection is triggered. By combining this dynamic triggering mechanism with selection of blocks having valid data ratio below the threshold, the system ensures sufficient free blocks are restored while minimizing write amplification, achieving a dynamic balance between these two objectives.
Data Source
AI summary
A controller is configured to execute a garbage collection operation on a nonvolatile memory including blocks, which includes calculating a write amplification; calculating a first threshold changing as a number of first blocks changes based on a number of first blocks storing valid data; increasing the first threshold when the calculated write amplification is less than a target value of the write amplification, decreasing the first threshold when the calculated write amplification is greater than the target value; specifying a valid data ratio indicating a ratio of a total amount of valid data to a total amount of data able to be stored in one block for each of the first blocks; selecting each block with the corresponding valid data ratio less than the first threshold from the first blocks; and setting each selected block to a free block by copying valid data stored therein to a copy destination block.