Chapter 10 Virtual Memory
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Catégorie :Category: nCreator TI-Nspire
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Shortlink : http://ti-pla.net/a4610748
Type : Classeur 3.0.1
Page(s) : 1
Taille Size: 2.21 Ko KB
Mis en ligne Uploaded: 29/04/2025 - 18:56:04
Uploadeur Uploader: no_name0908 (Profil)
Téléchargements Downloads: 1
Visibilité Visibility: Archive publique
Shortlink : http://ti-pla.net/a4610748
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Fichier Nspire généré sur TI-Planet.org.
Compatible OS 3.0 et ultérieurs.
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VIRTUAL MEMORY BASICS Virtual address space logical view of how a process is stored in memory Physical address space actual available frames in memory DEMAND PAGING Bring pages into memory from the swap space as needed Keep track of this using a valid bit. If the bit is set the page is in memory, otherwise it is in secondary storage only The page is not in memory and must be brought in from secondary storage. This is a page fault Pure demand paging start with zero pages in memory, fault with every new page we bring in Assume a program has referenced a virtual memory address. Under what conditions could each of the following occur: " TLB miss with no page fault: Page not in TLB but is in RAM " TLB miss with page fault: Page not in TLB or in RAM " TLB hit with no page fault: Page in TLB and in RAM " TLB hit with page fault.: Not possible COPY ON WRITE allows both parent and child processes to initially share the same pages in memory In general, free pages are allocated from a pool of zero-fill-on-demand pages PAGE REPLACEMENT Prevent over allocation of memory by modifying page-fault service routine to include page replacement Use modify bit to reduce overhead of page transfers only modified pages are written to disk PAge replacement completes the seperation between logical and physcial memory BASIC PAGE REPLACEMENT 1. Find the location of the desired page on disk 2. Find a free frame: " If there is a free frame, use it " If there is no free frame, use a page replacement algorithm to select a victim frame. Write victim frame to disk if dirty 3. Bring the desired page into the (newly) free frame; update the page and frame tables 4. Continue the process by restarting the instruction that caused the trap PAGE REPLACEMENT ALGORITHMS FIFO: First in First Out Optimal: Replaces the page that wil not be used for the longest period of time LRU: REplaces the page that has not been used in the most amount of time Made with nCreator - tiplanet.org
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Compatible OS 3.0 et ultérieurs.
<<
VIRTUAL MEMORY BASICS Virtual address space logical view of how a process is stored in memory Physical address space actual available frames in memory DEMAND PAGING Bring pages into memory from the swap space as needed Keep track of this using a valid bit. If the bit is set the page is in memory, otherwise it is in secondary storage only The page is not in memory and must be brought in from secondary storage. This is a page fault Pure demand paging start with zero pages in memory, fault with every new page we bring in Assume a program has referenced a virtual memory address. Under what conditions could each of the following occur: " TLB miss with no page fault: Page not in TLB but is in RAM " TLB miss with page fault: Page not in TLB or in RAM " TLB hit with no page fault: Page in TLB and in RAM " TLB hit with page fault.: Not possible COPY ON WRITE allows both parent and child processes to initially share the same pages in memory In general, free pages are allocated from a pool of zero-fill-on-demand pages PAGE REPLACEMENT Prevent over allocation of memory by modifying page-fault service routine to include page replacement Use modify bit to reduce overhead of page transfers only modified pages are written to disk PAge replacement completes the seperation between logical and physcial memory BASIC PAGE REPLACEMENT 1. Find the location of the desired page on disk 2. Find a free frame: " If there is a free frame, use it " If there is no free frame, use a page replacement algorithm to select a victim frame. Write victim frame to disk if dirty 3. Bring the desired page into the (newly) free frame; update the page and frame tables 4. Continue the process by restarting the instruction that caused the trap PAGE REPLACEMENT ALGORITHMS FIFO: First in First Out Optimal: Replaces the page that wil not be used for the longest period of time LRU: REplaces the page that has not been used in the most amount of time Made with nCreator - tiplanet.org
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