计算机架构 资料 501W15_slideset06

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ENCM 501 W15 Lectures Slide Set 6
ቤተ መጻሕፍቲ ባይዱ
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Pages
The basic unit of virtual memory is called a page.
The size of a page in bytes must be a power of two. Different systems have different page sizes, and some instances a single system will support two or more different page sizes at the same time.
Suppose you enter the command gcc foo.c bar.c
A flurry of processes will come and go—one for the driver program gcc, two invocations of the compiler cc1, two invocations of the assembler as, and one invocation of the linker.
ENCM 501 W15 Lectures Slide Set 6
How VM provides memory protection
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The kernel gives a virtual address space to each process.
Suppose P is a process. P can use its own virtual address space with
The kernel is a vital piece of software—once it is running, it controls hardware—memory, file systems, network interfaces, etc.—and schedules the access of other running programs to processor cores.
VM preliminaries: Examples of processes
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Suppose you are typing a command into a terminal window on Linux system. Two processes are directly involved: the terminal and a shell—the shell is the program that interprets your commands and launches other programs in response to your commands.
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ENCM 501 W15 Lectures Slide Set 6
Caches and Virtual Memory
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(This slide is a repeat from Set 5.)
Both are essential systems to support applications running on modern operating systems. As mentioned two weeks ago, it really helps to keep in mind what problems are solved by caches and what very different problems are solved by virtual memory.
Then if you enter the command ./a.out, a process will be created from the executable you just built.
ENCM 501 W15 Lectures Slide Set 6
#1 problem solved by VM: protection
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ENCM 501 W15 Lectures Slide Set 6
Outline of Slide Set 6
Virtual memory: Introduction and preliminaries Pages, Translation, Page Tables and TLBs VM example: 64-bit Linux on x86-64 Notes about TLB operation TLBs and page tables for x86-64 Virtual memory and file systems Context switches Memory systems: Closing remarks (for a while . . . )
ENCM 501 W15 Lectures Slide Set 6
VM preliminaries: Processes
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A process can be defined as an instance of a program in execution.
Because the kernel has special behaviour and special powers not available to other running programs, the kernel is usually not considered to be a process.
ENCM 501 W15 Lectures Slide Set 6
VM preliminaries: The O/S kernel
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When a computer with an operating system is powered up or reset, instructions in ROM begin the job of copying a special program called the kernel from the file system into memory.
Processes never know the physical DRAM addresses of the memory they use. The addresses used by processes are virtual addresses, which get translated into physical addresses for access to memory circuits. Translations are managed by the kernel.
Slide Set 6
for ENCM 369 Winter 2015 Lecture Section 01
Steve Norman, PhD, PEng
Electrical & Computer Engineering Schulich School of Engineering University of Calgary
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Processes need to be able to access memory quickly but safely.
It would be disastrous if a process could accidentally or maliciously access memory in use for kernel instructions or kernel data.
ENCM 501 W15 Lectures Slide Set 6
Outline of Slide Set 6
Virtual memory: Introduction and preliminaries Pages, Translation, Page Tables and TLBs VM example: 64-bit Linux on x86-64 Notes about TLB operation TLBs and page tables for x86-64 Virtual memory and file systems Context switches Memory systems: Closing remarks (for a while . . . )
A very common page size is 4 KB. How many 4 KB pages are available in a system with 8 GB of memory?
Winter Term, 2015
ENCM 501 W15 Lectures Slide Set 6
Contents
Virtual memory: Introduction and preliminaries Pages, Translation, Page Tables and TLBs VM example: 64-bit Linux on x86-64 Notes about TLB operation TLBs and page tables for x86-64 Virtual memory and file systems Context switches Memory systems: Closing remarks (for a while . . . )
no risk that P will access other processes’ memory; no risk other processes will access P’s memory. (That is a slight oversimplification—modern OSes allow intentional sharing of memory by cooperating processes.)