Hybrid-LRU Caching Scheme for PDRAM Hybrid
Memory Architecture in Cloud Computing
Hongtianchen Xie
1
, Gangyong Jia
1,2
, Guangjie Han
3
, Jian Wan
4
, Yongjian Ren
1
, Jie Huang
1
, Xindong You
1
1
Department of Computer Science and Technology, Hangzhou Dianzi University
Hangzhou, 310018, China
2
Key Laboratory of Complex Systems Modeling and Simulation, Ministry of Education
Hangzhou, 310018, China
3
Department of Information & Communication Systems, Hohai University
Changzhou, 213022, China
4
School of Information and Electronic Engineering, Zhejiang University of Science and Technology
Hangzhou, 310023
gangyong@hdu.edu.cn; hanguangjie@gmail.com
Abstract—In recent years, the mixed memory (PDRAM)
which is consisted of the phase-change memory (PRAM) and the
conventional memory (DRAM) has drawn a lot of attention from
both industry and academia. It is a promising alternative to
replace the traditional memory architecture. PDRAM has good
characteristics as large capacity, good stability and non-volatile,
while PRAM has disadvantages of a limited life and large access
latency. Traditional policies are not sufficient to be directly
applied to the PDRAM memory architecture. They cannot adapt
to the new features of the hybrid architecture because of their
undifferentiated operation, extensive use of PRAM can cause
performance degradation and shorten the life of PDRAM
memory. This paper proposed Hybrid-LRU caching scheme to
address these problems. Our scheme mainly uses the cache
consistency address resolution mode to distinguish between
different physical mediums in PDRAM, and then take different
actions depending on different physical mediums. We have taken
a variety of tradition policies like LRU, FIFO, RANDOM,
CFLRU to make experimental comparisons. The experimental
results have shown that our scheme can reduce the PRAM
utilization rate of 11.8% and improve the performance by 4.6%,
energy consumption of write and read operation can be reduced
up to 88.2%.
Keywords: phase change memory;hybrid memory architecture;
cache policy;performance; energy.
I. INTRODUCTION
With the rapid development of technology, the topic of big
data storage and processing capability is widespread concern.
But as we know, DRAM memory is the traditional memory
medium which has almost reached the limit of integration (1).
We have to reconsider the memory architecture in the face of
increasing storage and high performance requirements. Phase
change memory (PRAM) is one of the most popular new
storage medium, which has virtues of its high-density storage,
byte addressable, non-volatile and many other advantages to
win the favor of both industry and academia. Samsung
Electronics tried to use PRAM in mobile phones in 2010 (2)
and present a 20nm 1.8V 8G PRAM at the 2012 International
Solid State Circuits Symposium (3).
PRAM (4, 5) is a kind of chalcogenide material storage
medium, which is changing the phase state to change the data
state. Read and write process can be divided into three parts:
Set (write “1”), Reset (write “0”) and Read. PRAM needs to
take more time to write than read because of its higher
temperature. But the way of storing data is stable enough
because PRAM would not change its state even the power is
off. We can summarize PRAM’s properties and the differences
with DRAM just like below:
a) High-density storage (6)
Phase change material can change its resistance value with
different voltage. This property can be used to packing more
bytes in the same size block because different resistance values
can store different combinations of bytes. It means PRAM
would have larger storage on the same size memory as DRAM.
b) Non-volatile
Phase change material can change its status with controlling
internal temperature. Its storage capability is much stable than
DRAM because data storage would not be effected by power
supply (7).
c) Byte-addressable
DRAM is byte-addressable storage material. Flash memory
has the same attributes as Non-volatile just like PRAM. But
flash memory cannot apply to the hybrid memory with DRAM
because it's a kind of block-addressable storage material.
TABLE I. COMPARISON BETWWEN PRAM AND DRAM
d) Lower energy consumption
DRAM need to constantly refreshed to keep data while
PRAM does not. And voltage of 0.2~0.4V is enough to get
PRAM to work. As shown in TABLE1, although PRAM’s
operation energy is 3 times as much as DRAM’s, but PRAM