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Linux memory management. Linux uses demand paging where the virtual pages are only loaded into physical memory when needed by the process. Swapping occurs when a process needs to bring data from the virtual memory to the physical memory,

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Introduction

Linux Memory Management

Memory management is an important part of a computers operating system, even from the early days a program will require more and more memory than actually exists. A strategy to overcome this is to use a virtual memory, virtual memory make a system appear that it has more memory as it shares it with other processes. The memory management sub system in Linux provides

  • Large address spaces
  • Protection
  • Memory Mapping
  • Fair physical memory allocation
  • Shared virtual memory

 In a virtual memory system all of the addresses are virtual and not physical. The page table converts virtual to physical addresses. Each of the physical and virtual memory is split up into pages, usually the same size .On alpha AXP the page sizes are 8 Kbytes and on Intel x86 systems the pages are 4kbytes.

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Middle

technique to efficiently choose pages which are to be removed from the system. This scheme requires every page in the system having an age which changes as the page is accessed. The more frequently that a page is accessed, the younger it is; the less that it is accessed the older it becomes. Old pages are good candidates for swapping. The Linux kernel is not run in the virtual address space instead it is solely allocated space in the physical memory address. The page table in Linux also controls access to the code as well as mapping, e.g. the processor has two modes user and kernel, you won’t allow access of kernel code to users and vice versa to protect your system.
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Conclusion

Dis – Advantages:

  • The drawback of using caches, hardware or otherwise, is that in order to save effort Linux must use more time and space maintaining these caches and, if the caches become corrupted, the system will crash.

Advantages:

  • Page tables are so successful that Linux uses the same page table manipulation code for the Alpha processor, which has three levels of page tables and for Intel x86 processors, which have two levels of page tables.
  • Linux memory management is better for older computers as it can sometimes require less processing power than other operating systems.

Resources:

  • http://tldp.org/LDP/tlk/mm/memory.html
  • http://www.inf.fu-berlin.de/lehre/SS01/OS/Lectures/Lecture14.pdf
  • Ehttp://www.makelinux.com/ldd3/chp-15-sect-1

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