LBM: A Low-power Buffer Management Policy for Heterogeneous Storage in Mobile Consumer Devices

Transcription

1 LBM: A Low-power Buffer Management Policy for Heterogeneous Storage in Mobile Consumer Devices Hyojung Kang Department of Computer Science, Ewha University, Seoul, Korea Junseok Park Semiconductor Business, Samsung Electronics Co., Ltd., Gyeonggi-do, Korea Hyokyung Bahn Department of Computer Science, Ewha University, Seoul, Korea IEEE Transactions on Consumer Electronics, 2010

2 Outline Introduction Related Works Proposed Scheme Performance Evaluation Conclusions

3 Introduction (1/2) desirable properties of NAND flash memory Small size Lightweight Shock resistance Low-power consumption Using mobile disk and NAND flash memory together as secondary storage is an alternative solution to provide large storage capacity with reasonable cost

4 Introduction (2/2) LBM (Low-power Buffer Management) considers Different energy consumption rate of each storage device I/O operation type (read and write) The reference potential of blocks in terms of both recency and frequency

5 Two architectures Related Works use flash memory as a nonvolatile cache of disks, making the spin-down time of disk longer equally uses both mobile disk and flash memory as secondary storage Two different ways of buffer management in heterogeneous storage architecture to partition the buffer cache space to different storage devices, and then each partitioned space is managed separately to use the buffer cache space as a pool and does not partition the cache space for each storage device

6 when Hit SEQ DAC (Device-Aware Cache replacement )scheme RAN LRU Hard Disk MRU LRU flash memory MRU when Miss (set C_SEQ=1, C_RAND=3 ) RAN SEQ RAN LRU Hard Disk MRU LRU flash memory miss count = 10 2 miss count = 01 after every W references, adjusting partitions.. delta = 2 1 = 1 MRU

7 Proposed Scheme (1/6) Aim to design a buffer management policy specially focusing on the minimization of power consumption Device power-consumption Operation type In NAND flash, servicing a write requires about eight times larger cost than servicing a read Reference potential Power consumption can be reduced when blocks in the buffer hit Estimate the re-reference likelihood of buffered blocks

8 Proposed Scheme (2/6) Estimate the re-reference likelihood of a buffered blocked based on previous reference behaviors Assume that a block referenced recently or frequently in the past is likely to be re-referenced soon Extend the CRF (combined recenecy/frequency) concept of the LRFU policy Distinguish read and write references in contributing to CRF in order to consider the asymmetric read/write cost of flash memory

9 Proposed Scheme (3/6) weight function F(δ) = μ δ (0<μ<1) δ: the time span from the reference in the past to the current time t c CRF(i) = r(i) F(δ 1 )+r(i) F(δ 2 )+w(i) F(δ 3 ) δ 1 = tc t1, δ 2 = tc t2, δ 3 = tc t3 considering both recency and frequency F(δ) δ

10 time A A B C A C D : read : write t = R*0.9^2+W*0.9 R*0.9^6+W*0.9^5+R*0.9^0 R*0.9^4+W*0.9^3 R*0.9^9+W*0.9^7+R*0.9^3 = 10.8 = = Block i A B C CRF( i ) cache is full, need to evict a block weight function F(δ) = μ δ (0<μ<1) in this example, set u = 0.9, R=1, W=10 Value(i) = Weight dv (i) * CRF(i) Weight dv denotes the basic power consumption of the device needed to access block i block from disk is given more weight replace the smallest-value block

11 Proposed Scheme (5/6) the applicability of a buffer management policy depends heavily on the time and space efficiency in LBM policy, computing the Value of each block requires all of the past reference times impractical as space overhead for maintaining this information LBM does not need to maintain the full reference history of a block

12 Value of non-referenced block i can be computed directly from a recently computed Value the relative ordering of the non-referenced blocks in the buffer cache does not changed maintained by a min heap data structure where the time complexity of all operations on this DS is O(log n)

13 Performance Evaluation (1/4) Trace-driven simulations with MTRON MSD-SATA flash SSD Hitachi Travelstar 5K100 mobile disk

14 Performance Evaluation (2/4) Three file I/O traces collected by executing various applications on the FreeBSD Files are allocated to flash memory and mobile disk by the ratio of 2:8 μ is set to by empirical analysis

15 Performance Evaluation (3/4) Traces 1 and 2 contain significant number of frequently referenced blocks with long reference interval, LBM outperform LRU and LRFU Trace 2 and 3, LRFU sometimes performs worse than LRU, LRFU may cache blocks from less expensive storage in terms of power consumptions if the blocks have larger CRF values

16 Performance Evaluation (4/4) LBM performs worse than LRU and LRFU in some cases weights of LBM are mainly set to reduce power consumption rather than I/O time

17 Conclusions Propose a new buffer cache management policy for heterogeneous storage Aim at reducing power consumption By considering different energy-consumption rate of each device and I/O type, the reference potential of blocks (recency & frequency) Reduces power consumption by 18% on average and up to 58.9%, and also improves the total I/O time Future Work Using volatile RAM as buffer cache may not guarantee the consistency of file system Use nonvolatile memory to cache dirty blocks