virtual memory management in multi processor mach os
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Virtual memory management in multi-processor Mach OS allows processes to access more memory than is physically installed by using virtual addresses. The Mach kernel provides basic services like tasks, threads, messages, and ports to enable parallel and distributed applications. Tasks have their own virtual address spaces that are divided into pages which are allocated to physical frames. The virtual memory system provides protection at the page level by using protection codes in page table entries to control read, write, and execute permissions.
virtual memory management in multi processor mach os
- 1. Virtual Memory Management in Multi Processor MACH OS By- Ajay Kharat ID: 2019H1030011G
- 2. • Mach OS is designed for multiprocessor, parallel and distributed environments. • Mach OS itself run in parallel and supports:- -All algorithm are designed to run in parallel. -All Data structure can access in parallel. • Virtual memory system:- A computer can address more memory than the amount physically installed on the system. Overview
- 3. Topics • Design Issues • Mach Kernel • Task Address Space • Memory Protection Abbrevation: VMS- Virtual Memory system
- 4. Design Issues • Portability: Ability of OS to run on several machine with different architecture. For wide spread of any OS, portability is important consideration in design of VMS. • Data Sharing: In Multiprocessor system, application run as collection of processes that run on different processor.
- 5. • Protection: Multiple programs in main memory, OS must protect address space of each process from unauthorized access. • Efficiency Virtual memory system can become a bottleneck and limit the performance of multiprocessor OS because of address translation, page table lookup, page replacement, etc…
- 6. Mach Kernel • Mach Kernel provides only basic primitive for building parallel and distributed applications. Other OS services, which are useful to end users are built on top of Mach kernel.
- 7. Mach Kernel provides only a small no. of simple services, it has some benefits: - • More reliable (less code is running in Kernel mode) • Easier to extend micro kernel • Easier to port Mach OS to new architecture (Portable) Mach Kernel support some abstraction: - Task & Thread: - A Task is collection of threads and thread is smallest unit of execution. Threads has it’s own PC and set of register.
- 8. • Message: Message is collection of data used by threads for communication/synchronization on multiprocessor system while this threads are running in parallel on different processor. • Port: It is uni-directional channel associated with each process/thread that queue up message for that object. Process and Thread communicate with each other by performing send() and receive() operation on their ports.
- 9. Task Address Space • Size of any address space (RAM) is limited by no. of bits in Memory Address Register(MAR). • Mach OS follows non contiguous memory allocation, where virtual address space of process is divided into pages and this process pages are allocated in hardware paged (frame) in physical memory. • Process page size may be multiple of hardware page size.
- 10. Virtual Memory system • Virtual address issued by a process is valid only if , it falls in allocated region of that process virtual address space. • But Mach Virtual memory system supports some operations needed in advance application: - • Normally, thread can only access address space of task in which it executes but sometime it is necessary for a task to read or write in address space of other task. • E.g. Debugger needs to examine and modify the address space of the task it is debugging • Mach virtual memory system provides primitive to perform this operation.
- 11. Memory Protection • In Mach virtual memory system, memory protection is implemented at page level. • Each allocated page has two protection codes associated with it: - 1. Current protection code:- This protection code in Page table, specify whether page can be reference or not. 2. Maximum protection code:- This protection code in Page table, specify the limit value for current protection.
- 12. Cont. Page table entry for protection: Every time a page is referred, maximum protection code value is decremented. Also it maintain Read, write and execute permission in page table for memory protection.
- 13. THE END