Comparison and Review of Memory Allocation and File Access Techniques and Techniques preferred for Distributed Systems

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1 Comparison and Review of Memory and File Access Techniques and Techniques preferred for Muazzam A. Khan, Nauman Nisar, Department of Computer Engineering, College of Electrical and Mechanical Engineering, National University of Sciences and Technology,Islamabad, Pakistan. Abstract Memory is a process in which operating system manages the Primary Memory and allocates user programs in spaces in the Main Memory. File Access is a process in which the files required to execute are accessed within in the Main Memory and brought to the CPU. Memory and file access methods play an important role in optimizing the CPU performance and primary memory performance. The paper focuses on the techniques that are applied for memory allocation and file retrieval and comparison of the techniques which performs better is environment. This paper will also enlist some of the good features that should be included within techniques for memory allocation and file access within. Keywords: Memory, File Access Methods, Memory Management, Memory Techniques. 1. Introduction systems are referred to as distributed computing systems; distributed system is a set of systems that acts like a one large computer. There are a lot of distributed computing systems projects on the Internet that helps in solving complex and difficult problems by sharing their resources by using different people s computers processing and other resources [1]. Memory management is the part of an operating system which manages primary and main memory. Memory management keeps complete record of all memory location in the main memory either it is allocated to a process or it is not allocated or free. It keeps record of memory, which is to be allocated to processes an processors. It decides which process should be delivered to memory at what time. It keeps record of the memory when it is freed or unallocated and maintains its status accordingly. The main role of the memory management is to satisfy the requests made by processes in order to get executed by the processor [1].Whenever new processes in created it requests for memory or sometimes during execution some more memory is needed by the invoked processes. In both the cases the main memory should be capable to provide such memory space for the processes that made request. Main memory has two types of partitions. One is Low Memory in which the operating system is assigned and other one is Memory: User processes are kept and allocated in that part of the memory. Some systems use Pages for memory allocation and some use segments for memory allocation. Paged allocation partition the computer's main/primary memory into fixed-size frames or units called Page frames, and the program's allocated space into the pages of the one fixed

2 size [15]. Segmentation is the only memory allocation and management technique that does not entertain user's program while giving them a 'linear and contiguous address space. There are two types of memory allocation and that are Single Contiguous and Partitioned. File access is a method of accessing files within the main memory. For the purpose two registers are used commonly, a base register and a limit register. The base register holds the smallest legal physical memory address and the limit register specifies the size of the range. For example, if the base register holds and the limit register is , then the program can legally access all addresses from through [8]. Section 2 will discuss literature review and related work in the paper. Section 3 will discuss various techniques of memory allocation in OS. Section 4 will compare different techniques of memory allocation and determine which technique is better for which types of systems. Section 5 will discuss about techniques for memory allocation and file access that should be used for distributed systems, recommendations and conclusions derived from this whole research and finally section 6 has references of resources from where paper is researched. 2. Related Work This section will discuss about the search engines that were used for the research of the paper and the keywords that were used in it to make research and also will include the related work in which different techniques that were represented. The search engines used for getting the relevant data are listed as follows: Google Scholars IEEE Explorer Springer Explorer Cite Seer Explorer The keywords used to search relevant papers. All the citing is done using these keywords: and Memory Management Memory Management. Memory in Memory Management. With conventional SMP systems, multiple processors execute instructions in a single address space.. It is possible to run parts of a program in parallel, generally by using threads to specify such parallelism and using synchronization primitives to prevent race conditions. shared memory is a technique for making multicomputer easier to program by simulating a shared address space on them. Different models are discussed in these notes for shared memory [15]. The methodology and the results of Malloc function which is one of necessities of memory management in distributed environment is presented in [1]. Modern software requires and adds an increasing reliance in dynamic memory allocation but the direct management is always error-prone. So Garbage Collection (part of Memory Management) eliminates many of these bugs [3][2]. Rainbow OS needs no locks for accessing memory or shared objects during executions. It uses an optimistic synchronization, allowing transactions to proceed locally and its validation at the end of it an example of distributed virtual memory [4]. 3. Memory Techniques In this section we will discuss techniques for user process memory management techniques

3 which are of two types one internal to process and others are external to process [12]. Internal to process techniques / schemes are Segments. Process memory is divided into logical segments such as text, data, heap and stack etc. Some of them are read only, others are read-write. Some are known at compile time and some of them grow dynamically as process progress [7]. Static s. These are done at compile time and done using heaps and stacks. Dynamic. As static allocation is not enough for heaps and stacks. Dynamic storage need is necessary because user not need to know about the allocation of memory to a process when it is executed. It requires two fundamental operations: allocate dynamic storage and free it when no longer needed. Stacks are good when it is predictable when to remove process from memory and Heap is good when it is not predictable when to remove the process from the memory. Heap-based dynamic memory allocation techniques typically maintain a free list, which keeps track of all the holes. These are done using algorithms such as Best Fit, Worst Fit and First Fit [9]. Garbage Collection. Freeing memory from unused programs automatically. It can take up to 50% of time for cleaning unused programs from memory which was spent to allocate them to memory [2]. External to process techniques / schemes are Static Relocation. Puts OS in the highest memory and assign each process a segment in which it fits perfectly and add address or its link with secondary memory logged [6]. Problems with static relocation are Safety of OS as Static relocation done process cannot take more size then when it was initialized and cannot move when it starts execution. Dynamic Relocation. In dynamic relocation there are two address spaces one is physical address space and other is virtual or logical address space [5]. Virtual Address is the address which seen by user or process but physical address space is space which is visible to operating system only. Different virtual addresses can reside in one location in physical address but they are known to users as different address spaces [4]. Swapping. The process of removing or relocating a process from the main memory to disk and maintaining its complete state on the disk for further use [14]. OS can restore space in memory by swapping the blocked or ready processes from the memory. Compaction. Dynamic relocation to the memory causes external fragmentation in the memory so for removing compaction is used in memory which moves the process so that memory allocation can be contiguous. Paging. In paging memory allocation technique data is fetched from disk in fixed size blocks called pages [13]. Paging is an important part of virtual memory management. As data is fetched in fixed size block the fragmentation occurs. Paging is a vital part of virtual memory implementation in most of the operating systems; it allows them to use disk storage for data that is not in physical randomaccess memory (RAM). Fig 1: Page Address Translation

4 4. Comparison This section of paper has results of comparison of memory allocation techniques that are used in main memory management. The parameters that are used for comparison are advantage; disadvantage and best for are used. Comparison is done in tabular form. We will discuss about techniques and file systems that have higher impact on, and Standalone. It is listed below in the table 1. Techniques Computation Required Frames / Blocks Size Time Fragmentation Best For Segments Low Variable Low Internal Static Low Fixed Low External Low ---- Dynamic Fixed, Variable Internal, External Static Relocation Low Variable Low External Low ---- Dynamic Relocation Swapping Variable, Fixed Fixed, Variable, Low Internal, External Internal, External Compaction ---- Removes it Paging Fixed Internal Modern Personal

5 Techniques Computation Required Frames / Blocks Size Time Fragmentation Best For TFS (Transparent File System) Low Fixed, Variable Low Internal (Low for Ordinary files) Clouds AFS (Andrew File System) NFS (Sun Network File System) GFS (Google File System) HFS (HADOOP FILE SYSTEM ) Variable Low ---- Variable Low ---- Variable ---- Variable ---- ( ) ( ) ( & Clusters) ( & Clusters) Table 1: Memory Management & File Access and Techniques Comparison. Standalone Standalone Cloud Based & Clusters Cloud Based & Clusters 5. Conclusion It is concluded and recommended that dynamic allocation and relocation for internal process and external process respectively are better for distributed systems because in distributed systems a large number of processes can be present at a time with similar priorities in queue at different sites. So dynamic allocation and reallocation of processes in distributed memories is required. These techniques can be merged with other techniques such as swapping and compaction in removing their fragmentation and replacing them with priority. In dynamic relocation paging is one of the best method to address space in different memories with multiple paging algorithms [13]. Thus each technique has its unique pros and cons, their variations can be useful in distributed systems some of which are discussed in [1][2][3][13] and [14] 6. References [1] Sam Toueg, Unreliable failure detectors for reliable distributed systems, Journal of the ASCM, [2] Eliot J., Moss B., Richard L. Hudson, Ron Morrison and David S. Munro, Training Garbage: The DMOS Collector, [3] Viral Kapadia, Comparative Study and Implementation of Garbage collection for Environment Using Client Server Approach in Train Algorithm M.E. Thesis

6 [4] M. Wende, Communcation model of a distributed virtual memory. Ph.D. thesis, Ulm University, [11] George Coulouris, Jean Dollimore, Tim Kindberg, : Concepts and Design, 4/e, [5] Huang Xian-ying, Wang Yue, Chen Yuan. Memory management strategy in embedded realtime system, Computer Engineering and Design, [6] S. Liang, R. Noronha, and D. K. Panda,, Swapping to Remote Memory over Infinite Band: An Approach using a Network Block Device, IEEE Cluster Computing, Sept [7] Xie Yinqiao, Li Guangjun, Memory management method of an embedded system based on Micro/OSII. University of Electronic Science and Technology, 2006(In Chinese) [8] H.Midorikawa, H.Koyama, M.Kurokawa, R.Himeno The Design of Large Memory System DLM and DLM Compiler, IEICE Technical Report. Computer systems, Vol.107, No.398, pp , 2007 [9] S. Tikar, and S. Vadhiyar, Efficient reuse of replicated parallel data segments in computational grids. Future Generation Computer 24, ( ) [10] Paul Krzyzanowski, Shared Memory and Memory Consistency Models. Rutgers University CS 417: Notes [12] Stallings, Operating, Prentice Hall, 3 rd edition, [13] M onica Serrano, Salvador Petit, Julio Sahuquillo, Rafael Ubal, Houcine Hassan, and Jos e Duato, Page-Based Memory Policies of Local and Remote Memory in Cluster Computers, IEEE 18th International Conference on Parallel and [14] Shogo Saito, Shuichi Oikawa, Exploration of non-volatile memory management in the OS kernel, Third International Conference on Networking and Computing, [15] KAPADIA V.V. & THAKORE D.G., Adaptive Memory Management for System by Memory and Deallocation, Journal of Information and Communications, [16] JAMES CIPAR, MARK D. CORNER and EMERY D. BERGER. Contributing Storage using the Transparent File System, ACM Transactions on Storage, Vol. V, No. N, Month 20YY. [17] Sunita Suralkar, Ashwini Mujumdar, Gayatri Masiwal and Manasi Kulkarni Review of File : Case Studies, International Journal of Engineering Research and Applications (IJERA) 2013.