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How Unix implements virtual memory?


 
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Homework and Emergencies Homework & Coursework Questions How Unix implements virtual memory?
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Old 09-03-2009
Computer How Unix implements virtual memory?

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1. The problem statement, all variables and given/known data:
The key to using memory most efficiently is virtual memory management. Consider both Windows and UNIX operating systems. Compare and contrast how each implements virtual memory. Describe how each one handles page faults, working sets, and page sizes, and how it reconciles thrashing issues. Cite your sources.


2. Relevant commands, code, scripts, algorithms:
there are no commands required.


3. The attempts at a solution (include all code and scripts):
no solution.


4. School (University) and Course Number:
Mapua Institute of Technology - Information Technology

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svatophys(9r)															     svatophys(9r)

NAME
svatophys - General: Converts a system virtual address to a physical address SYNOPSIS
kern_return_t svatophys( vm_offset_t kern_addr, vm_offset_t *phys_addr ); ARGUMENTS
Specifies the kernel virtual address. Specifies a pointer to the physical address to be filled in. DESCRIPTION
The svatophys routine converts a system virtual address to the corresponding physical address. All address and data structure manipulation done within the kernel is performed using system virtual addresses. Typically, system virtual addresses are a means of mapping physical memory and I/O space, which often consists of device registers and DMA buffers. In contrast to this, devices are usually unaware of any virtual addressing and for this reason use physical addresses. You use the svatophys routine to perform this address translation. As an example of where you can use this address translation, a disk device driver can use DMA buffers to transfer blocks of data to the disk (for the case of a write operation). The data to be written to disk is present in system memory at a system virtual address known to the driver. To initiate the DMA operation, the disk driver can set up a command packet to specify a write operation to the underlying disk controller hardware. This write command packet contains (among other things) the location of the DMA buffer as a physical address and the length of the buffer. Here, the driver calls the svatophys routine to translate the system virtual address of the DMA buffer to a physical address in the command packet issued to the disk driver. RETURN VALUES
The svatophys routine returns the following: The address translation has been completed successfully. Unable to perform address transla- tion. This value indicates that the address specified by the kern_addr argument is not a valid kernel or system virtual address. svatophys(9r)

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