Lecture 12 Virtual Memory

Lecture 12 Virtual Memory - CS M151B / EE M116C Computer...

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Reinman 12-1 CS M151B / EE M116C Computer Systems Architecture Virtual Memory Some notes adopted from Dean Tullsen and Larry Carter at UCSD
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Reinman 12-2 Virtual Memory • Goal: every process thinks it has a huge memory entirely to itself. – Virtual address space: addresses 0 to 2 32 –1 • (or 0 to 2 64 –1 on machines with 64-bit addressing). • even if there is much less physical memory. – Virtual memory also provides protection • One process can’t corrupt the data of another • Another user, running on the same machine, can’t see your data
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Reinman 12-3 Virtual Memory • Can be seen as another level in the memory hierarchy – Main memory is a cache of a larger memory space. – Disk holds data in VM that doesn’t fit in cache – VM may be bigger than disk cpu cache memory disk virtual memory If a process doesn’t use the entire virtual memory, there will be addresses that have no storage assigned.
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Reinman 12-4 There can be many virtual address spaces physical addresses virtual addresses virtual addresses disk
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Reinman 12-5 Virtual Memory • For historical reasons, it uses different terminology Cache VM block (line) page cache miss page fault address virtual address
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Reinman 12-6 How VM differs from memory caches • MUCH higher miss penalty (millions of cycles)! – Therefore: – large pages [analogous to cache line] (4 KB to MBs) – associative mapping of pages (typically fully associative) – software handling of misses (but HW handles hits!!) – write-through never used, only write-back
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This note was uploaded on 04/18/2010 for the course CS 151B taught by Professor N/a during the Spring '10 term at UCLA.

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Lecture 12 Virtual Memory - CS M151B / EE M116C Computer...

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