Publications by Yixin Luo

@inproceedings{abc,
	abstract = {NAND flash memory density continues to scale to keep up with the increasing storage demands of data-intensive applications. Unfortunately, as a result of this scaling, the lifetime of NAND flash memory has been decreasing. Each cell in NAND flash memory can endure only a limited number of writes, due to the damage caused by each program and erase operation on the cell. This damage can be partially repaired on its own during the idle time between program or erase operations (known as the dwell time), via a phenomenon known as the self-recovery effect. Prior works study the self-recovery effect for planar (i.e., 2D) NAND flash memory, and propose to exploit it to improve flash lifetime, by applying high temperature to accelerate selfrecovery. However, these findings may not be directly applicable to 3D NAND flash memory, due to significant changes in the design and manufacturing process that are required to enable practical 3D stacking for NAND flash memory. In this paper, we perform the first detailed experimental characterization of the effects of self-recovery and temperature on real, state-of-the-art 3D NAND flash memory devices. We show that these effects influence two major factors of NAND flash memory reliability: (1) retention loss speed (i.e., the speed at which a flash cell leaks charge), and (2) program variation (i.e., the difference in programming speed across flash cells). We find that self-recovery and temperature affect 3D NAND flash memory quite differently than they affect planar NAND flash memory, rendering prior models of self-recovery and temperature ineffective for 3D NAND flash memory. Using our characterization results, we develop a new model for 3D NAND flash memory reliability, which predicts how retention, wearout, self-recovery, and temperature affect raw bit error rates and cell threshold voltages. We show that our model is accurate, with an error of only 4.9\%. Based on our experimental findings and our model, we propose HeatWatch, a new mechanism to improve 3D NAND flash memory reliability. The key idea of HeatWatch is to optimize the read reference voltage, i.e., the voltage applied to the cell during a read operation, by adapting it to the dwell time of the workload and the current operating temperature. HeatWatch (1) efficiently tracks flash memory temperature and dwell time online, (2) sends this information to our reliability model to predict the current voltages of flash cells, and (3) predicts the optimal read reference voltage based on the current cell voltages. Our detailed experimental evaluations show that HeatWatch improves flash lifetime by 3.85{\texttimes} over a baseline that uses a fixed read reference voltage, averaged across 28 real storage workload traces, and comes within 0.9\% of the lifetime of an ideal read reference voltage selection mechanism.},
	author = {Yixin Luo and Saugata Ghose and Yu Cai and Erich F. Haratsch and Onur Mutlu},
	booktitle = {Proceedings of the 24th International Symposium on High-Performance Computer Architecture (HPCA)},
	title = {HeatWatch: Improving 3D NAND Flash Memory Device Reliability by Exploiting Self-Recovery and Temperature-Awareness},
	venue = {Vienna, Austria},
	year = {2018}
}

@inproceedings{abc,
	abstract = {Digital forensic investigators often need to extract data from a seized device that contains NAND flash memory. Many such devices are physically damaged, preventing investigators from using automated techniques to extract the data stored within the device. Instead, investigators turn to chip-off analysis, where they use a thermal-based procedure to physically remove the NAND flash memory chip from the device, and access the chip directly to extract the raw data stored on the chip.

We perform an analysis of the errors introduced into multi-level cell (MLC) NAND flash memory chips after the device has been seized. We make two major observations. First, between the time that a device is seized and the time digital forensic investigators perform data extraction, a large number of errors can be introduced as a result of charge leakage from the cells of the NAND flash memory (known as data retention errors). Second, when thermal-based chip removal is performed, the number of errors in the data stored within NAND flash memory can increase by two or more orders of magnitude, as the high temperature applied to the chip greatly accelerates charge leakage. We demonstrate that the chip-off analysis based forensic data recovery procedure is quite destructive, and can often render most of the data within NAND flash memory uncorrectable, and, thus, unrecoverable.

To mitigate the errors introduced during the forensic recovery process, we explore a new hardware- based approach. We exploit a fine-grained read reference voltage control mechanism implemented in modern NAND flash memory chips, called read-retry, which can compensate for the charge leakage that occurs due to (1) retention loss and (2) thermal-based chip removal. The read-retry mechanism successfully reduces the number of errors, such that the original data can be fully recovered in our tested chips as long as the chips were not heavily used prior to seizure. We conclude that the read-retry mechanism should be adopted as part of the forensic data recovery process. },
	author = {Aya Fukami and Saugata Ghose and Yixin Luo and Yu Cai and Onur Mutlu},
	booktitle = {Proceedings of the 2017 Digital Forensics Conference},
	title = {Improving the Reliability of Chip-Off Forensic Analysis of NAND Flash Memory Devices},
	venue = {{\"U}berlingen, Germany},
	year = {2017}
}

@inproceedings{abc,
	author = {Yu Cai and Saugata Ghose and Yixin Luo and Ken Mai and Onur Mutlu and Erich F. Haratsch},
	booktitle = {2017 IEEE International Symposium on High Performance Computer Architecture, HPCA 2017, Austin, TX, USA},
	title = {Vulnerabilities in MLC NAND Flash Memory Programming: Experimental Analysis, Exploits, and Mitigation Techniques.},
	url = {https://doi.org/10.1109/HPCA.2017.61},
	year = {2017}
}

@article{abc,
	author = {Yu Cai and Saugata Ghose and Erich F. Haratsch and Yixin Luo and Onur Mutlu},
	journal = {CoRR},
	title = {Error Characterization, Mitigation, and Recovery in Flash Memory Based Solid-State Drives.},
	url = {http://arxiv.org/abs/1706.08642},
	year = {2017}
}

@article{abc,
	author = {Yixin Luo and Saugata Ghose and Tianshi Li and Sriram Govindan and Bikash Sharma and Bryan Kelly and Amirali Boroumand and Onur Mutlu},
	journal = {CoRR},
	title = {Using ECC DRAM to Adaptively Increase Memory Capacity.},
	url = {http://arxiv.org/abs/1706.08870},
	year = {2017}
}

@article{abc,
	author = {Yixin Luo and Sriram Govindan and Bikash Sharma and Mark Santaniello and Justin Meza and Aman Kansal and Jie Liu and Badriddine M. Khessib and Kushagra Vaid and Onur Mutlu},
	journal = {CoRR},
	title = {Heterogeneous-Reliability Memory: Exploiting Application-Level Memory Error Tolerance.},
	url = {http://arxiv.org/abs/1602.00729},
	year = {2016}
}

@inproceedings{abc,
	author = {Yixin Luo and Saugata Ghose and Yu Cai and Erich F. Haratsch and Onur Mutlu},
	booktitle = {IEEE Journal on Selected Areas in Communications},
	title = {Enabling Accurate and Practical Online Flash Channel Modeling for Modern MLC NAND Flash Memory.},
	url = {http://dx.doi.org/10.1109/JSAC.2016.2603608},
	year = {2016}
}

@inproceedings{abc,
	author = {Yu Cai and Yixin Luo and Saugata Ghose and Onur Mutlu},
	booktitle = {45th Annual IEEE/IFIP International Conference on Dependable Systems and Networks, DSN 2015, Rio de Janeiro, Brazil},
	title = {Read Disturb Errors in MLC NAND Flash Memory: Characterization, Mitigation, and Recovery.},
	url = {http://dx.doi.org/10.1109/DSN.2015.49},
	year = {2015}
}

@inproceedings{abc,
	author = {Yixin Luo and Yu Cai and Saugata Ghose and Jongmoo Choi and Onur Mutlu},
	booktitle = {IEEE 31st Symposium on Mass Storage Systems and Technologies, MSST 2015, Santa Clara, CA, USA},
	title = {WARM: Improving NAND flash memory lifetime with write-hotness aware retention management.},
	url = {http://dx.doi.org/10.1109/MSST.2015.7208284},
	year = {2015}
}

@inproceedings{abc,
	author = {Yu Cai and Yixin Luo and Erich F. Haratsch and Ken Mai and Onur Mutlu},
	booktitle = {21st IEEE International Symposium on High Performance Computer Architecture, HPCA 2015, Burlingame, CA, USA},
	title = {Data retention in MLC NAND flash memory: Characterization, optimization, and recovery.},
	url = {http://dx.doi.org/10.1109/HPCA.2015.7056062},
	year = {2015}
}

@inproceedings{abc,
	author = {Yixin Luo and Sriram Govindan and Bikash Sharma and Mark Santaniello and Justin Meza and Aman Kansal and Jie Liu and Badriddine M. Khessib and Kushagra Vaid and Onur Mutlu},
	booktitle = {44th Annual IEEE/IFIP International Conference on Dependable Systems and Networks, DSN 2014, Atlanta, GA, USA},
	title = {Characterizing Application Memory Error Vulnerability to Optimize Datacenter Cost via Heterogeneous-Reliability Memory.},
	url = {http://dx.doi.org/10.1109/DSN.2014.50},
	year = {2014}
}

@inproceedings{abc,
	author = {Vivek Seshadri and Yoongu Kim and Chris Fallin and Donghyuk Lee and Rachata Ausavarungnirun and Gennady Pekhimenko and Yixin Luo and Onur Mutlu and Phillip B. Gibbons and Michael A. Kozuch and Todd C. Mowry},
	booktitle = {The 46th Annual IEEE/ACM International Symposium on Microarchitecture, MICRO-46, Davis, CA, USA},
	title = {RowClone: fast and energy-efficient in-DRAM bulk data copy and initialization.},
	url = {http://doi.acm.org/10.1145/2540708.2540725},
	year = {2013}
}