• Journal of the Korea Society of Computer and Information
• /
• v.23 no.3
• /
• pp.1-8
• /
• 2018

In this paper, we propose a new page replacement policy using recency and frequency on hybrid main memory. The proposal has two features. First, when a page fault occurs in the main memory, the proposal allocates it to DRAM, regardless of operation types such as read or write. The page allocated by the page fault is likely to be high probability of re-reference in the near future. Our allocation can reduce the frequency of write operations in PCM. Second, if the write operations are frequently performed on pages of PCM, the pages are migrated from PCM to DRAM. Otherwise, the pages are maintained in PCM, to reduce the number of unnecessary page migrations from PCM. In our experiments, the proposal reduced the number of page migrations from PCM about 32.12% on average and reduced the number of write operations in PCM about 44.64% on average, compared to CLOCK-DWF. Moreover, the proposal reduced the energy consumption about 15.61%, and 3.04%, compared to other page replacement policies.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.28 no.4
• /
• pp.919-928
• /
• 2018

Out-Of-Bounds (OOB) is one of the most powerful vulnerabilities in heap memory. The OOB vulnerability allows an attacker to exploit unauthorized access to confidential information by tricking the length of the array and reading or writing memory of that length. In this paper, we propose a method to automatically detect OOB vulnerabilities in heap memory using dynamic symbol execution and shadow memory table. First, a shadow memory table is constructed by hooking heap memory allocation and release function. Then, when a memory access occurs, it is judged whether OOB can occur by referencing the shadow memory, and a test case for causing a crash is automatically generated if there is a possibility of occurrence. Using the proposed method, if a weak block search is successful, it is possible to generate a test case that induces an OOB. In addition, unlike traditional dynamic symbol execution, exploitation of vulnerabilities is possible without setting clear target points.

• Journal of KIISE:Computing Practices and Letters
• /
• v.14 no.7
• /
• pp.708-712
• /
• 2008

Existing dynamic memory allocation schemes for general purpose operating system can not directly apply to the wireless sensor networks (WSNs). Because these schemes did not consider features of WSNs, they consume a lot of energy and waste the memory space caused by fragmentation. In this paper, we found features of WSNs applications and made the model which adapts these issues. Through this research, we suggest the slab allocator that reduces the execution time and the memory management space. Also, we evaluate the performance of our scheme by comparing to one of the previous systems.

• Journal of KIISE:Computing Practices and Letters
• /
• v.13 no.7
• /
• pp.476-487
• /
• 2007

Flash memory offers attractive features, such as non-volatile, shock resistance, fast access, and low power consumption for data storage. However, it has one main drawback of requiring an erase before updating the contents. Furthermore, flash memory can only be erased limited number of times. To overcome limitations, flash memory needs a software layer called flash translation layer (FTL). The basic function of FTL is to translate the logical address from the file system like file allocation table (FAT) to the physical address in flash memory. In this paper, a new FTL algorithm called an efficient and advanced space-management technique (EAST) is proposed. EAST improves the performance by optimizing the number of log blocks, by applying the state transition, and by using reallocation blocks. The results of experiments show that EAST outperforms FAST, which is an enhanced log block scheme, particularly when the usage of flash memory is not full.

• Journal of Computing Science and Engineering
• /
• v.6 no.4
• /
• pp.287-293
• /
• 2012

We introduce a methodology for the study of the application-level performance of time-sharing parallel jobs on a set of compute nodes in high performance clusters and report our findings. We assume that parallel jobs arriving at a cluster need to share a set of nodes with the jobs of other users, in that they must compete for processor time in a time-sharing manner and other limited resources such as memory and I/O in a space-sharing manner. Under the assumption, we developed a methodology to simulate job arrivals to a set of compute nodes, and gather and process performance data to calculate the percentage slowdown of parallel jobs. Our goal through this study is to identify a better combination of jobs that minimize performance degradations due to resource sharing and contention. Through our experiments, we found a couple of interesting behaviors for overlapped parallel jobs, which may be used to suggest alternative job allocation schemes aiming to reduce slowdowns that will inevitably result due to resource sharing on a high performance computing cluster. We suggest three job allocation strategies based on our empirical results and propose further studies of the results using a supercomputing facility at the San Diego Supercomputing Center.

• The Transactions of the Korea Information Processing Society
• /
• v.6 no.9
• /
• pp.2311-2319
• /
• 1999

We present two heuristic algorithms for the task allocation problem (NP-complete problem) in parallel computing. The problem is to find an optimal mapping of multiple communicating tasks of a parallel program onto the multiple processing nodes of a distributed-memory multicomputer. The purpose of mapping these tasks into the nodes of the target architecture is the minimization of parallel execution time without sacrificing solution quality. Many heuristic approaches have been employed to obtain satisfactory mapping. Our heuristics are based on genetic algorithms and simulated annealing. We formulate an objective function as a total computational cost for a mapping configuration, and evaluate the performance of our heuristic algorithms. We compare the quality of solutions and times derived by the random, greedy, genetic, and annealing algorithms. Our experimental findings from a simulation study of the allocation algorithms are presented.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.15 no.6
• /
• pp.49-58
• /
• 2005

In this paper, we have proposed a secure dynamic ID allocation protocol using mutual authentication on the RFID tag. Currently, there are many security protocols focused on the low-price RFID tag. The conventional low-price tags have limitation of computing power and rewritability of memory. The proposed secure dynamic ID allocation protocol targets to the high-performance RFID tags which have more powerful performance than conventional low-price tag by allocating dynamic ID to RFID using mutual authentication based on symmetric encryption algorithm. This protocol can be used as a partial solution for ID tracing and forgery.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.54 no.4
• /
• pp.217-223
• /
• 2005

In this paper, we have proposed a secure dynamic ID allocation protocol using mutual authentication on the RFID tag. Currently, there are many security protocols focused on the low-price RFID tag. The conventional low-price tags have limitation of computing power and rewritability of memory. The proposed secure dynamic ID allocation protocol targets to the high-performance RFID tags which have more powerful performance than conventional low-price tag by allocating a dynamic ID to RFID using mutual authentication based on symmetric encryption algorithm. This protocol can be used as a partial solution for ID tracing and forgery.

• Korean Journal of Cognitive Science
• /
• v.24 no.2
• /
• pp.133-171
• /
• 2013

The gist of a scene can be identified in less than 100msec, and violation in the gist can influence the way to allocate attention to the parts of a scene. In other words, people tend to allocate more attention to the object(s) inconsistent with the gist of a scene and to have better memory of them. To investigate the effects of contextual consistency on the attention allocation and object memory, two experiments were conducted. In both experiments, a $3{\times}2$ factorial design was used with scene presentation time(2s, 5s, and 10s) as a between-subject factor and object-background contextual consistency(consistent, inconsistent) as a within-subject factor. In Experiment 1, eye movements were recorded while the participants viewed line-drawing scenes. The results showed that the eye movement patterns were different according to whether the scenes were consistent or not. Context-inconsistent objects showed faster initial fixation indices, longer fixation times, more frequent returns than context-consistent ones. These results are entirely consistent with those of previous studies. If an object is identified as inconsistent with the gist of a scene, it attracts attention. Furthermore, the inconsistent objects and their locations in the scenes were recalled better than the consistent ones and their locations. Experiment 2 was the same as Experiment 1 except that a dual-task paradigm was used to reduce the amount of attention to allocate to the objects. Participants had to detect the positions of the probe occurring every second while they viewed the scenes. Nonetheless, the result patterns were the same as in Experiment 1. Even when the amount of attention to allocate to the scene contents was reduced, the same effects of contextual inconsistency were observed. These results indicate that the object-background contextual consistency has a strong influence on the way of allocating attention and the memory of objects in a scene.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.48 no.5
• /
• pp.74-82
• /
• 2011

SSD has a limitation of number of erase/write cycles and does not allow in-place update unlike the hard disk because SSD is composed of an array of NAND flash memory. Thus, FTL is used to effectively manage SSD of having different characteristics from traditional disk. FTL has page, block, log-block mapping method. Among then, when log-block mapping method such as BAST and FAST is used, the performance of SSD is degraded because frequent merge operations cause lots of pages to be copied and deleted. This paper proposes a data allocation and replacement method based on access frequency by allocating PRAM as checking area of access frequency, log blocks, storing region of hot data in SSD. The proposed method can enhance the performance and lifetime of SSD by storing cold data to flash memory and storing log blocks and frequently accessed data to PRAM and then reducing merge and erase operations. Besides, a data replacement method is used to increase utilization of PRAM which has limitation of capacity. The experimental results show that the ratio of erase operations of the proposed method is 46%, 38% smaller than those of BAST and FAST and the write performance of the proposed method is 34%, 19% higher than those of BAST and FAST, and the read performance of the proposed method is 5%, 3% higher than those of BAST and FAST, respectively.