Page Fault

Paging
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Paging

Most virtual memory systems use a technique called paging, which we will now explain. On any computer, programs reference a set of memory addresses. When a program implements an instruction like

The WSClock Page Replacement Algorithm
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The WSClock Page Replacement Algorithm

The main working set algorithm is unwieldy, since the entire page table has to be scanned at each page fault until a suitable candidate is located. An improved algorithm, that is based on the clock algorithm but also uses the working set information, is called WSClock (Carr and

Instruction Backup
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Instruction Backup

When a program references a page that is not in memory, the instruction causing the fault is stopped partway through and a trap to the operating system takes place. After the operating system has fetched the page required, it must restart the instruction causing the trap. This

Separation of Policy and Mechanism
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Separation of Policy and Mechanism

An important tool for managing the complexity of any system is to separate policy from mechanism. This principle can be applied to memory management by having most of the memory manager run as a user-level process. Such a separation was first done in Mach (Young et al.,

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