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80 lines
3.4 KiB
80 lines
3.4 KiB
第二次作业
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OS concept ver7课本第8章、第九章的习题：
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8.3 Given ?ve memory partitions of 100 KB, 500 KB, 200 KB, 300 KB,and
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600 KB (in order), how would each of the ?rst-?t, best-?t, and worst-?t
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algorithms place processes of 212 KB, 417 KB, 112 KB, and 426 KB (in
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order)?Which algorithm makes the most ef?cient use of memory?
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8.4 Most systems allow programs to allocate more memory to its address
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space during execution.Data allocated in the heap segments of programs
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is an example of such allocated memory. What is required to support
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dynamic memory allocation in the following schemes:
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a. contiguous-memory allocation
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b. pure segmentation
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c. pure paging
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8.12 Consider the following segment table:
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Segment Base Length
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0 219 600
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1 2300 14
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2 90 100
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3 1327 580
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4 1952 96
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What are the physical addresses for the following logical addresses?
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a. 0,430
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b. 1,10
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c. 2,500
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d. 3,400
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e. 4,112
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9.5 Assume we have a demand-paged memory. The page table is held in
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registers. It takes 8 milliseconds to service a page fault if an empty page
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is available or the replaced page is not modi?ed, and 20 milliseconds if
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the replaced page is modi?ed. Memory access time is 100 nanoseconds.
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Assume that the page to be replaced is modi?ed 70 percent of the time.
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What is the maximum acceptable page-fault rate for an effective access
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time of no more than 200 nanoseconds?
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9.13 A page-replacement algorithm should minimize the number of page
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faults. We can do this minimization by distributing heavily used pages
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evenly over all of memory, rather than having them compete for a small
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number of page frames.We can associatewith each page frame a counter
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of the number of pages that are associated with that frame. Then, to
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replace a page, we search for the page frame with the smallest counter.
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a. De?ne a page-replacement algorithmusing this basic idea. Specif-
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ically address the problems of (1) what the initial value of the
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counters is, (2) when counters are increased, (3) when counters
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are decreased, and (4) how the page to be replaced is selected.
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b. Howmany page faults occur for your algorithmfor the following
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reference string, for four page frames?
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1, 2, 3, 4, 5, 3, 4, 1, 6, 7, 8, 7, 8, 9, 7, 8, 9, 5, 4, 5, 4, 2.
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c. What is the minimumnumber of page faults for an optimal page-
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replacement strategy for the reference string in part b with four
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page frames?
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实验相关
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------------------
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1 lab1的proj1的ucore的代码中是否有使用了绝对地址（编译期间指定的绝对内存地址）？
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2 lab2 的ucore的小os的load addr和link addr分别是多少?
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3 ucore用了哪个数据结构来管理空闲内存，位于内存什么地方，占多少空间？
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4 请考虑在ucore中实现second chance/enhanced clock页替换算法的设计思路。主要描述如何利用相关x86相关硬件、如何设计数据结构，大致要实现哪些函数，函数的大致功能和整体流程。
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5 实现enhanced clock algorithm中，
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IF before clock sweep: (used,dirty) = (1,1), THEN after clock sweep: (used, dirty)=(0,1).
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如果把上述转换改为：
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IF before clock sweep: (used,dirty) = (1,1), THEN after clock sweep: (used, dirty)=(1,0).
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是否可行？
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6 在clock算法实现中，pte中的uesd bit位是否可以让os来设置1 or 0 ? 为什么？
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7 在enhanced clock算法中的dirty bit位是否可以让os来设置1 or 0 ? 为什么？
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8 如果在ucore中实现精确的LRU算法，如何设计？需要硬件和OS分别完成什么事情？
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