From e308c20039e04106694a4d2d9fee7d78ff581c36 Mon Sep 17 00:00:00 2001 From: chyyuu Date: Sat, 12 Oct 2013 09:08:26 +0800 Subject: [PATCH] release homework 2 --- homework/hw2.txt | 69 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) create mode 100644 homework/hw2.txt diff --git a/homework/hw2.txt b/homework/hw2.txt new file mode 100644 index 0000000..5d7c973 --- /dev/null +++ b/homework/hw2.txt @@ -0,0 +1,69 @@ +第二次作业 + +OS concept ver7课本第8章、第九章的习题: + +8.3 Given ?ve memory partitions of 100 KB, 500 KB, 200 KB, 300 KB,and +600 KB (in order), how would each of the ?rst-?t, best-?t, and worst-?t +algorithms place processes of 212 KB, 417 KB, 112 KB, and 426 KB (in +order)?Which algorithm makes the most ef?cient use of memory? + +8.4 Most systems allow programs to allocate more memory to its address +space during execution.Data allocated in the heap segments of programs +is an example of such allocated memory. What is required to support +dynamic memory allocation in the following schemes: +a. contiguous-memory allocation +b. pure segmentation +c. pure paging + +8.12 Consider the following segment table: +Segment Base Length +0 219 600 +1 2300 14 +2 90 100 +3 1327 580 +4 1952 96 +What are the physical addresses for the following logical addresses? +a. 0,430 +b. 1,10 +c. 2,500 +d. 3,400 +e. 4,112 + +9.5 Assume we have a demand-paged memory. The page table is held in +registers. It takes 8 milliseconds to service a page fault if an empty page +is available or the replaced page is not modi?ed, and 20 milliseconds if +the replaced page is modi?ed. Memory access time is 100 nanoseconds. +Assume that the page to be replaced is modi?ed 70 percent of the time. +What is the maximum acceptable page-fault rate for an effective access +time of no more than 200 nanoseconds? + + +9.13 A page-replacement algorithm should minimize the number of page +faults. We can do this minimization by distributing heavily used pages +evenly over all of memory, rather than having them compete for a small +number of page frames.We can associatewith each page frame a counter +of the number of pages that are associated with that frame. Then, to +replace a page, we search for the page frame with the smallest counter. +a. De?ne a page-replacement algorithmusing this basic idea. Specif- +ically address the problems of (1) what the initial value of the +counters is, (2) when counters are increased, (3) when counters +are decreased, and (4) how the page to be replaced is selected. +b. Howmany page faults occur for your algorithmfor the following +reference string, for four page frames? +1, 2, 3, 4, 5, 3, 4, 1, 6, 7, 8, 7, 8, 9, 7, 8, 9, 5, 4, 5, 4, 2. +c. What is the minimumnumber of page faults for an optimal page- +replacement strategy for the reference string in part b with four +page frames? + +实验相关 +------------------ + +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)? + +2 lab2 的ucore的小os的load addr和link addr分别是多少? + +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? + +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。 + +5 实现enhanced clock algorithm 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 ?