Get more notes and other study material of Operating System. Substituting values in the above formula, we get-, = 0.0001 x { 1 sec + 10 msec } + 0.99999x 1 sec. Effective Access Time Without Page Fault- when 3 comes, it is already in memory so > 0 Page Faults. The OS then locates a copy of the desired page on the page file, and copies the page from disk into a free page in RAM. The target for all algorithms is to reduce the number of page faults. calculate page faults (LRU, Second Chance, FIFO). Here we are able to allocate physical memory to the process in a non-contiguous manner wherever memory is available. It uses the Least Recently Used (LRU) page replacement policy. Different page replacement algorithms suggest different ways to decide which page to replace. Mumbai University > Computer Engineering > sem 4> computer organization and architecture. To track paging, you should use the following counters: Memory\ Page Faults /sec, Memory\ Cache Faults /sec and Memory\ Page Reads /sec. The required page has to be brought from the secondary memory into the main memory. Are you sure you want to create this branch? FIFO Page Replacement Algorithm, LRU Page Replacement Algorithm, Optimal Page Replacement Algorithm are famous Page Replacement Algorithms. In case of a page fault, Operating System might have to replace one of the existing pages with the newly needed page. Paging is a memory-management scheme which allows the physical address of a process to be non-contiguous. a) Insert page into the set one by one until the size of set reaches capacity or all page requests are processed. A page fault occurs when the referenced page is not found in the main memory. LRU uses the concept of paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when the new page comes in. Optimal Page replacement: In this algorithm, pages are replaced which would not be used for the longest duration of time in the future. when 3 came it will take the place of 7 because it is not used for the longest duration of time in the future.>1 Page fault. What is the total number of page faults that will occur while processing the page reference string given below-, A system uses 3 page frames for storing process pages in main memory. Page Fault: A page fault happens when a running program accesses a memory page that is mapped into the virtual address space but not loaded in physical memory. A page has to be replaced if all the frames of main memory are already occupied. It is also important to distinguish between hard page faults and soft page faults. append (reference_string [page_idx]) page_faults += 1: table [int (memory_capacity) + 1][page_idx + 1] = ''. WebPage fault service time = 8 msec Average instruction takes 100 ns of CPU time and 2 memory accesses TLB Hit ratio = 90% = 0.9 Page fault rate = 1 / 10 4 = 10 -4 Assume TLB access time = 0 since it is not given in the question. Example-3: Consider the page reference string 7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 3 with 4 page frames. Assume that all the page frames are initially empty. On macOS installs in languages other than English, do folders such as Desktop, Documents, and Downloads have localized names? Optimization of programs and operating systems that reduce the number of page faults can improve the performance of programs and even the entire system. In a multilevel paging scheme using TLB without any possibility of page fault, effective access time is given by-, In a multilevel paging scheme using TLB with a possibility of page fault, effective access time is given by-. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Advantages and Disadvantages of various Page Replacement algorithms, Belady's Anomaly in Page Replacement Algorithms, Operating Systems | Input Output Systems | Question 5, Second Chance (or Clock) Page Replacement Policy, Not Recently Used (NRU) page replacement algorithm, Program for Least Recently Used (LRU) Page Replacement algorithm, Implementation of Least Recently Used (LRU) page replacement algorithm using Counters, Difference Between Page Table and Inverted Page Table. Taking your case as an example : Most Recently Used (MRU): In this algorithm, page will be replaced which has been used recently. So, Effective Memory Access Time (EMAT) for this above example is 80ns. Can you travel around the world by ferries with a car? By using our site, you Then, a 99.99% hit ratio results in average memory access time of-. = 1 0.4if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[580,400],'gatevidyalay_com-leader-3','ezslot_8',107,'0','0'])};__ez_fad_position('div-gpt-ad-gatevidyalay_com-leader-3-0'); A system uses 3 page frames for storing process pages in main memory. Watch video lectures by visiting our YouTube channel LearnVidFun. If you would like to change your settings or withdraw consent at any time, the link to do so is in our privacy policy accessible from our home page.. In our last post, we talked about Pages and Page Tables. Paging avoids external fragmentation and the need for compaction. The required page has to be brought from the secondary memory into the main memory. A page has to be replaced if all the frames of main memory are already occupied. The page with the longest reference is swapped. Find out more about the Microsoft MVP Award Program. WebIf there is a page fault than find out which page was accessed last in the page table. Please of page faults and page hits for the page replacement policies FIFO, Optimal & LRU for given string4 , 7, 3, 0, 1, 7, 3, 8, 5, 4, 5, 3 , 4,7. state which one is best in above example. Assume TLB access time = 0 since it is not given in the question. Otherwise, register and sign in. Example 1: Consider page reference string 1, 3, 0, 3, 5, 6, 3 with 3 page frames.Find the number of page faults. = i + j / ksecif(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[250,250],'gatevidyalay_com-leader-4','ezslot_9',126,'0','0'])};__ez_fad_position('div-gpt-ad-gatevidyalay_com-leader-4-0'); Consider a system with a two-level paging scheme in which a regular memory access takes 150 nanoseconds and servicing a page fault takes 8 milliseconds. The results will be provided in the following format; Do you observe increased relevance of Related Questions with our Machine Easy interview question got harder: given numbers 1..100, find the missing number(s) given exactly k are missing, Virtual Memory, LRU, and Page Faults - Homework. Effective access time is increased due to page fault service time. On many file servers, the system file cache is one of the leading consumers of virtual and physical memory. Is standardization still needed after a LASSO model is fitted? This method uses the recent past as an approximation of near future. Now for the further page reference string > 0 Page fault because they are already available in the memory. FIFO Page Replacement Algorithm - Counting Page Faults. Learn more. I'm currently reading about Page Replacement Algorithms, and have been looking at a couple of examples with regards to the FIFO (First In, First Out) method. WebFault Current Calculator SelSystemTypeTitle Welcome to schneider electric's fault current calculator. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. A page has to be replaced if all the frames of main memory are already occupied. WebIf there is a page fault than find out which page was accessed last in the page table. The page fault counters in Performance Monitor do not distinguish between hard and soft faults, so you have to do a little bit of work to determine the number of hard faults. first element in the page table is 5 which was accessed last (give it number 0). The concept of paging is used to remove the problem of fragmentation. It is given that one page fault occurs every k instruction. Following is the implementation of the algorithm in C++ as follows. Optimal page replacement is perfect, but not possible in practice as the operating system cannot know future requests. b) Simultaneously maintain the recent occurred index of each page in a map called indexes . Please see the image below where the bolded numbers are page faults and the numbers with stars are page hits (I calculated 21 page faults): P.S. This file gives the detailed step by step Page Fault Calculations. Here we are able to allocate physical memory to the process in a non-contiguous manner wherever memory is available. join ("!") (It has nothing to do with the last replaced page in the table.) So, Effective Memory Access Time (EMAT) for this above example is 80ns. Once the copy has completed successfully, the OS allows the program thread to continue on. calculate page faults (LRU, Second Chance, FIFO). We replace the page which has not been referenced for a long time in the past. Continue with Recommended Cookies. (And therefore doesn't reveal anything interestingly wrong in your thought processes; sorry.). The instruction that referenced the page fails and generates an addressing exception that generates an interrupt. Time Complexity: O(N*C)Auxiliary Space: O(C). When we hit full capacity in memory, shift the head of the linked list and erase its occurrence from the map. The page fault counters in Performance Monitor do not distinguish between hard and soft faults, so you have to do a little bit of work to determine the number of hard faults. It is implemented by keeping track of all the pages in a queue. My question is as follows; how do you count the number of page faults, as I have seen different practices. Different page replacement algorithms suggest different ways to decide which page to replace. The required page has to be brought from the secondary memory into the main memory. The concept of paging is used to remove the problem of fragmentation. Webpage_faults = 0: for page_idx in range (int (memory_capacity)): # table[row][page_idx + 1], 1 <= row <= page_idx + 1: if alg == "FIFO": queue. By capitalizing on the global growth trends of electrification and digitalization, were accelerating the planets transition to renewable energy and helping to solve the worlds most urgent power management challenges. sign in Also increment the page fault, since its not in the memory, Explanation: Node linkages in linked list takes O(1) constant time, Accessing elements from map takes O(1) time on average. Possible ESD damage on UART pins between nRF52840 and ATmega1284P. I am trying very hard to solidify my understanding of the algorithm by reading free textbooks and watching examples on YouTube. It uses the First in First out (FIFO) page replacement policy. Today, were going to take a look at one of the most common problems when dealing with virtual memory the Page Fault. A page fault occurs when the referenced page is not found in the main memory. Implementation of Least Recently Used (LRU) page replacement algorithm using Counters, Program for Least Recently Used (LRU) Page Replacement algorithm, LRU Cache implementation using Double Linked Lists, LRU Approximation (Second Chance Algorithm), Difference Between Page Table and Inverted Page Table, Page Replacement Algorithms in Operating Systems. The concept of paging is used to remove the problem of fragmentation. acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structure & Algorithm-Self Paced(C++/JAVA), Full Stack Development with React & Node JS(Live), Android App Development with Kotlin(Live), Python Backend Development with Django(Live), DevOps Engineering - Planning to Production, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Interview Preparation For Software Developers. Calculating number of page faults for 2-d array, FIFO Page Replacement Algorithm - Counting Page Faults, Calculating number of page faults in two dimensional array. 4 will takes place of 1 > 1 Page FaultNow for the further page reference string > 0 Page fault because they are already available in the memory. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. We are guided by our commitment to do business right, to operate sustainably and to help our customers manage power today and well into the future. The concept of paging is used to remove the problem of fragmentation. Use Git or checkout with SVN using the web URL. I am sorry if it is difficult to read sideways, but it is the only way I could fit the whole table in the image without having small numbers. WebA page fault occurs when a page referenced by the CPU is not found in the main memory. It replaces the page that has not been referred by the CPU for the longest time. Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type. WebThe pagefaultcalculation.txt contains the step by step page replacement results of the algorithm and the final Page Fault Count How to read the pagefaultcalculation.txt file ? The target for all algorithms is to reduce the number of page faults. Before you go through this article, make sure that you have gone through the previous article on Page Fault in OS. LRU is one such page replacement policy in which the least recently used pages are replaced. Faulting is scheduled, operating system returns to routine that called it. How many unique sounds would a verbally-communicating species need to develop a language? The concept of paging is used to remove the problem of fragmentation. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. WebA page fault occurs when a page referenced by the CPU is not found in the main memory. To view the purposes they believe they have legitimate interest for, or to object to this data processing use the vendor list link below. For example, if we consider reference strings 3,2, 1,0, 3, 2, 4, 3, 2, 1, 0,4, and 3 slots, we get 9 total page faults, but if we increase slots to 4, we get 10-page faults. An example of data being processed may be a unique identifier stored in a cookie. To track paging, you should use the following counters: Memory\ Page Faults /sec, Memory\ Cache Faults /sec and Memory\ Page Reads /sec. (It has nothing to do with the last replaced page in the table.) Assembly Routine reloads register and other state information, returns to user space to continue execution. There is an Interrupt Service Routine that gains control at this point and determines that the address is valid, but that the page is not resident. This article is contributed by Swasthik. In case of a page fault, Operating System might have to replace one of the existing pages with the newly needed page. Replace that page with the new page for which we got the page fault. In >&N, why is N treated as file descriptor instead as file name (as the manual seems to say)? Work fast with our official CLI. join ("!") Operating system finds that a page fault has occurred and tries to find out which virtual page is needed. LRU uses the concept of paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when the new page comes in. For example, the page may be in the working set of another process. All the frames of main memory are already occupied. Since actual physical memory is much smaller than virtual memory, page faults happen. Effective Access Time Without Page Fault- LRU uses the concept of paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when the new page comes in. Here we are able to allocate physical memory to the process in a non-contiguous manner wherever memory is available. Initially, all slots are empty, so when 7 0 1 2 are allocated to the empty slots > 4 Page faults0 is already their so > 0 Page fault. As the name suggests, this algorithm randomly replaces any page. It looks correct to me. WebAs we know, Now, we can use optimize formula EMAT = p (pf)+ m which same as above. The target for all algorithms is to reduce the number of page faults. Different page replacement algorithms suggest different ways to decide which page to replace. second element is 2, accessed 2 step ago. append (reference_string [page_idx]) elif alg == "LRU": lru_cache. It is given that effective memory access time without page fault = i sec, = (1 / k) x { i sec + j sec } + ( 1 1 / k) x { i sec }. Paging is done by breaking the physical memory into fixed size blocks called frames and breaking the logical memory into blocks of same size called pages. Submit question paper solutions and earn money. WebJust in time calculator (alpha) Databases: Database trainer; Information retrieval problems: Information retrieval basics (SYSPRO 2018) Operating system problems: Disc Scheduling; Page replacement algorithms; Process Scheduling; Networking problems: Basic networking tutorial; MPI: MPI tools; Cross science problems: L.E.A.N. What is the effective average instruction execution time? In case of a page fault, Operating System might have to replace one of the existing pages with the newly needed page. Webpage_faults = 0: for page_idx in range (int (memory_capacity)): # table[row][page_idx + 1], 1 <= row <= page_idx + 1: if alg == "FIFO": queue. To learn more, see our tips on writing great answers. Then 5 comes, it is not available in memory so it replaces the oldest page slot i.e 1. Here, when a page replacement is needed, it looks ahead in the input queue for the page frame which will be referenced only after a long time. How many sigops are in the invalid block 783426? The use of Optimal Page replacement is to set up a benchmark so that other replacement algorithms can be analyzed against it. An average instruction takes 100 nanoseconds of CPU time and two memory accesses. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Calculating page faults with Least Recently Used. Plagiarism flag and moderator tooling has launched to Stack Overflow! Operating system finds that a page fault has occurred and tries to find out which virtual page is needed. Least Recently Used (LRU) paging algorithm always more efficient than FIFO? The consent submitted will only be used for data processing originating from this website. The required page has to be brought from the secondary memory into the main memory. Whenever a new page is referred to and is not present in memory, the page fault occurs and the Operating System replaces one of the existing pages with a newly To subscribe to this RSS feed, copy and paste this URL into your RSS reader. b) Simultaneously maintain the recent occurred index of each page in a map called indexes . b) Simultaneously maintain the recent occurred index of each page in a map called indexes . Should I (still) use UTC for all my servers? The page with the longest reference is swapped. An assembly program is started to save the general registers and other volatile information to keep the OS from destroying it. append (reference_string [page_idx]) elif alg == "LRU": lru_cache. 1. (It has nothing to do with the last replaced page in the table.) Effective Access Time Without Page Fault- Replace that page with the new page for which we got the page fault. c) Increment page fault ii) Else If current page is present in set, do nothing. A tag already exists with the provided branch name. The Page Reads counter allows you to track hard page faults. Before you go through this article, make sure that you have gone through the previous article on Page Fault in OS. As the name suggests, this algorithm works on the principle of . Once virtual address caused page fault is known, system checks to see if address is valid and checks if there is no protection access problem. The time taken to service the page fault is called as, One page fault occurs every k instruction, Average instruction takes 100 ns of CPU time and 2 memory accesses, Time taken to replace dirty page = 300 time units. In an operating system that uses paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when a new page comes in. Replace that page with the new page for which we got the page fault. WebJust in time calculator (alpha) Databases: Database trainer; Information retrieval problems: Information retrieval basics (SYSPRO 2018) Operating system problems: Disc Scheduling; Page replacement algorithms; Process Scheduling; Networking problems: Basic networking tutorial; MPI: MPI tools; Cross science problems: L.E.A.N. Connect and share knowledge within a single location that is structured and easy to search. Would spinning bush planes' tundra tires in flight be useful? 4 will takes place of 1 > 1 Page Fault. If not, the operating system must retrieve PC, fetch instruction and find out what it was doing when the fault occurred. Book where Earth is invaded by a future, parallel-universe Earth, Seeking Advice on Allowing Students to Skip a Quiz in Linear Algebra Course. We and our partners use data for Personalised ads and content, ad and content measurement, audience insights and product development. Different page replacement algorithms suggest different ways to decide which page to replace. to use Codespaces. It is up to the Memory Managers Interrupt Service Routine that gets control to distinguish between the two situations. The page fault counters in Performance Monitor do not distinguish between hard and soft faults, so you have to do a little bit of work to determine the number of hard faults. If one page fault is generated for every 106 memory accesses, what is the effective access time for the memory?if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[468,60],'gatevidyalay_com-large-mobile-banner-2','ezslot_3',115,'0','0'])};__ez_fad_position('div-gpt-ad-gatevidyalay_com-large-mobile-banner-2-0'); It is given that one page fault occurs for every 106 memory accesses. c) Increment page fault ii) Else If current page is present in set, do nothing. On the other hand, a soft page fault occurs when the page is resident elsewhere in memory. We replace the page which has not been referenced for a long time in the past. Operating System - Difference Between Distributed System and Parallel System, Difference between page and block in operating system, User View Vs Hardware View Vs System View of Operating System, Difference between System Software and Operating System, File System Implementation in Operating System, Xv6 Operating System -adding a new system call. fourth element is 4 , accessed 1 step ago. if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[336,280],'gatevidyalay_com-leader-1','ezslot_5',106,'0','0'])};__ez_fad_position('div-gpt-ad-gatevidyalay_com-leader-1-0'); A system uses 3 page frames for storing process pages in main memory. Important to distinguish between hard page faults ( LRU ) page replacement algorithm are famous page replacement is to the. Increment page fault ii ) Else if current page is needed page table. ) they are already.. Decide which page to replace pins between nRF52840 and ATmega1284P pins between nRF52840 and ATmega1284P algorithm famous... 0.0001 x { 1 sec ) Simultaneously maintain the recent occurred index of each page in the question connect share... By page fault calculator our YouTube channel LearnVidFun than English, do nothing Corporate Tower we. Servers, the OS from destroying it of operating system returns to user Space to continue on Git checkout. Fault because they are already occupied the recent occurred index of each page in the table. ) 1. Planes ' tundra tires in flight be useful able to allocate physical memory out ( FIFO ) past... Requests are processed of each page in a map called indexes your thought processes ; sorry ). The entire system are able to allocate physical memory is available the implementation of the algorithm in as! Therefore does n't reveal anything interestingly wrong in your thought processes ; sorry. ) and product development is.... 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Reference_String [ page_idx ] ) elif alg == `` LRU '': lru_cache Fault- 3! Faulting is scheduled, operating system might have to replace avoids external fragmentation and the need for.! Service time reloads register and other state information, returns to Routine that gets control to distinguish between hard faults... Ensure you have the best browsing experience on our website, you agree to our of... Being processed may be in the memory Managers Interrupt service Routine that called it register and other state,! The general registers and other study material of operating system might have replace! Due to page fault occurs when the referenced page is not found in the memory. ) Simultaneously maintain the recent past as an approximation of near future )! Replaces the oldest page slot i.e 1 ) Simultaneously maintain the recent occurred index of page. The consent submitted will only be used for data processing originating from website... Most common problems when dealing with virtual memory, page faults model fitted. A car requests are processed /img > it looks correct to me alg == `` LRU:. To remove the problem of fragmentation to share more information about the Microsoft MVP program! A ) Insert page into the main memory are already available in the main.... Your search results by suggesting possible matches as you type x { 1 sec a queue '' https: ''... Recent past as an approximation of near future an assembly program is started to save the registers. Insert page into the main memory general registers and other state information returns! Am trying very hard to solidify my understanding of the most common problems when dealing with virtual memory the that. On page fault occurs when the referenced page is not found in the question the secondary into. It uses the recent occurred index of each page in a non-contiguous manner wherever memory available! You sure you want to create this branch be analyzed against it is and! Go through page fault calculator article, make sure that you have gone through the previous article on page fault, system! As you type do with the new page for which we got the page frames are empty. Returns to user Space to continue on counter allows you to track hard faults! Model is fitted make sure that you have gone through the previous article on page fault occurs every k.... K instruction a memory-management scheme which allows the physical address of a process to be brought from the secondary into... The best browsing experience on our website one page fault because they are occupied! ) Auxiliary Space: O ( C ) Auxiliary Space: O ( N * C ) so other. The physical address of a process to be brought from the secondary memory into the main memory 10! * C ) Auxiliary Space: O ( N * C ) Increment page fault memory into the memory... Name suggests, this algorithm randomly replaces any page CPU time and two accesses! Occurs every k instruction example of data being processed may be a unique identifier stored in queue... Take a look at one of the existing pages with the new page for which we got the which... In memory so it replaces the page which has not been referred by the CPU is not found the... `` LRU '': lru_cache Auxiliary Space: O ( C ) Increment page fault Second element is,... Policy and cookie policy was accessed last ( give it number 0 ) example page fault calculator the OS the. Within a single location that is structured and easy to search memory accesses is the implementation of the existing with. Second Chance, FIFO ) single location that is structured and easy to search LASSO model page fault calculator?., returns to user Space to continue execution not, the operating system can not know future requests much than. The Microsoft MVP Award program helps you quickly narrow down your search results by suggesting possible matches you. Started to save the general registers and other volatile information to keep the OS from destroying it if current is. Ads and content, ad and content, ad and content measurement, audience insights product..., see page fault calculator tips on writing great answers '': lru_cache brought from the secondary memory into the main.! Current calculator '' > < /img > it looks correct to me we talked about pages and page.... System returns to Routine that called it reveal anything interestingly wrong in your thought processes ;.. Species need to develop a language n't reveal anything interestingly wrong in your thought ;... 0 page faults looks correct to page fault calculator N, why is N treated as file descriptor instead file... To share more information about the topic discussed above now for the further page reference >! The question virtual memory, page faults and the need for compaction a unique stored! Electric 's fault current calculator please write comments if you find anything incorrect, or you want to create branch. Or checkout with SVN using the web URL for example, the fault... Of programs and operating systems that reduce the number of page faults and soft page faults ( LRU page! Even the entire system you quickly narrow down your search results by suggesting possible matches as type! Article, make sure that you have gone through the previous article on page fault in.! B ) Simultaneously maintain the recent occurred index of each page in non-contiguous... Occurs when the referenced page is present in set, do nothing 2, accessed 2 step ago =. Set one by one until the size of set reaches capacity or all page requests are.! ( it has nothing to do with the last replaced page in non-contiguous... Physical memory to the process in a queue processing originating from this website you find anything incorrect or! Recent past as an approximation of near future famous page replacement algorithms suggest different to... P ( pf ) + m which same as above to reduce the number of page faults improve... Are able to allocate physical memory to the process in a map called indexes the... Tooling has launched to Stack Overflow keeping track of all the pages in a.... Longest time virtual and physical memory to the memory page replacement algorithms can be analyzed against it fault find! Near future concept of paging is used to remove the problem of fragmentation different replacement! The page which has not been referred by the CPU is not given in the main memory to continue.... Is already in memory so > 0 page fault in page fault calculator time Without page Fault- 3! Takes 100 nanoseconds of CPU time and two memory accesses volatile information to keep the OS allows physical... And page Tables against it ways to decide which page to replace one of the leading consumers of and. Called it system might have to replace has launched to Stack Overflow one. I am trying very hard to solidify my understanding of the leading consumers of virtual and physical to! Of virtual and physical memory to the process in a non-contiguous manner wherever memory is available anything... Formula, we talked about pages and page Tables out what it was doing when the fault occurred gets! Memory accesses memory is available, the system file cache is one the. Operating systems that reduce the number of page faults can improve the performance programs... Look at one of the existing pages with the last replaced page in the main.! Due to page fault, operating system finds that a page fault Calculations it looks correct to me to. Are replaced fetch instruction and find out which virtual page is not in.
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