predictive garbage collection for flash memories
TRANSCRIPT
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Sai – 9th March’08
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NAND flash becoming more and more ubiquitous with promising features such as: very low power consumption compactness affordability, and so on
Flash memory management is quite involved and decides the effective bandwidth available to an application
Garbage Collection is a very time consuming process occurs only at a very less frequency, but determines worst-case
performance
Evening out garbage collection over idle periods in flash access can be very lucrative
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Mp3 player was run Occasional writes were issued to the device in parallel Bottom line: if the prescribed performance 128 kbps is maintained
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Greedy Approach:◦ Wu, M., Zwaenepoel, W., “eNVy: A Non-Volatile, Main Memory Storage
System,” 1994.
Cost-benefit policy:◦ Kawaguchi, A., Nishioka, S., and Motoda, H., “A Flash-Memory Based File
System,”, 1995.
Cost-Age-Time policy:◦ Mei-Ling Chiang, Paul C. H. Lee, Ruei-Chuan Chang, “Cleaning policies in
mobile computers using flash, 1999.
Real-Time Garbage Collection: Li-Pin Chang, Tei-Wei Kuo, Shi-Wu Lo, “Real-timegarbage collection for flash-
memory storage systems of realtimeembedded systems,” ,2004.
The Challenge:◦ addressing orthogonal requirements of wear-leveling, garbage
collection and utilization!!
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The device is used up to the full extent , so, a new allocation will call for the “clean-up” operation
The PROBLEM:◦ Very time consuming◦ Need to merge a huge amount of data, copy and
erase blocks for making space
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write_sect
Block First time being written?
· find_free_block
· write_page
· Update OOB
· Update Block Status
find_free_block
YES FAILURE
SUCCESS
DONE
· Complete GC
· write_sect
Page First time being written?
NO
· write_page
· Update OOB
· Update Page StatusYES
Free block exists?
Replacement Block Exists ?
NO
Replacement Block Free?
· fold
· write_sect
NO
YES
YES
NO
NO
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Is there an efficient prediction algorithm that can work for a variety of workloads for application-adaptive management of flash memory?
How to dynamically optimize orthogonal metrics of power and bandwidth of NAND flash?
Implement the above two on a flash simulator and demonstrate gains