DerekChiou_EE360N_Spring2010_Lecture12

DerekChiou_EE360N_Spring2010_Lecture12 - Lecture 12:...

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Unformatted text preview: Lecture 12: Virtual Memory Finale Lecture 12: Virtual Memory Finale and Interrupts/Exceptions Prof. Derek Chiou University of Texas at Austin Derek Chiou 1 Test of size Announcements Announcements z Exam this coming Wednesday z To be held in normal classroom z To be held in normal classroom z Seating will be assigned and your picture will be taken z Be sure to get here on time z Exam will end promptly at 6:15PM z Any paper is allowed, nothing else z We will not provide _any_ documentation, so bring yours z LC-3b ISA manual, etc. z Saving paper! z Will not be here tomorrow z Office hours extended by one hour tonight (6:30PM-8:30PM) z Can ask questions by Blackboard z Make appointments with TAs 3/1/2010 2 Test of size Recap/Outline Recap/Outline z Recap z VAX translation z VAX translation z Outline z Finish up virtual memory z Demand paging z Virtual memory and caching z Interrupts and Exceptions 3/1/2010 3 Test of size Demand Paging 3/1/2010 4 Test of size Demand Paging and Virtual Memory Demand Paging and Virtual Memory z Translation determines if page is in memory and an address z ( cache access ) z On page fault (page not valid), bring page into memory z ( cache replacement ) z OS finds empty page in memory (free list) z OS finds page on disk (if touched before) z OS reads page into memory z Write backs of modified pages? z ( cache writeback ) z When done? z When done? z Free page lists 3/1/2010 5 z FIFO or LIFO? Test of size Support for Paging the Page Table Support for Paging the Page Table z Page table entries (PTEs) only contain physical addresses z PTEs in primary memory contain primary or secondary memory addresses z PTEs in secondary memory contains only secondary memory addresses z Page table page cannot be thrown out before all its pages in primary memory thrown out z Special untranslated addressing mode required if page tables are traversed in software z Sparc: Translation disabled processor state z Alpha: Special kseg segment whose addresses are not translated. PTs mapped to kseg z Protection mode in processor necessary to maintain integrity of translation process 3/1/2010 6 translation process z Dont let a user process modify the page table, only trusted code Test of size Replacement Policy Replacement Policy z When referenced page not in primary memory, must be brought in brought in z If no free page available, page needs to be thrown back to secondary memory z which page should be replaced? z Generally Least Recently Used (LRU) policy used z replacement policy in software 3/1/2010 7 Test of size Implementing Pseudo-LRU Implementing Pseudo LRU Field in PTE maintained by software 1 - not a candidate for replacement i.e., recently referenced a candidate for replacemen 1 1 0 - a candidate for replacement i.e., not recently referenced How is table updated when there is a 1 1 How is table updated when there is a page fault or a TLB miss?...
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This note was uploaded on 09/23/2010 for the course EE 360n taught by Professor Staff during the Spring '08 term at University of Texas at Austin.

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DerekChiou_EE360N_Spring2010_Lecture12 - Lecture 12:...

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