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→Technology: rewrite to clarify the size of descriptors and page offsets in 4-level and 5 level scheme, as well as the Intel VA64 patent |
→Drawbacks: clarify the improvements in Intel VA64 patent |
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== Drawbacks ==
Adding another level of indirection makes [[page table]] "walks" longer.<ref>{{Cite conference|title=CSALT: Context Switch Aware Large TLB|book-title=MICRO-50: the 50th Annual IEEE/ACM International Symposium on Microarchitecture : proceedings |___location=Cambridge, MA|publisher=Institute of Electrical and Electronics Engineers., IEEE Computer Society., ACM Special Interest Group on Microprogramming|doi=10.1145/3123939.3124549|page=450|isbn=978-1-4503-4952-9|oclc=1032337814|date = 14 October 2017}}</ref> A page table walk occurs when either the processor's [[memory management unit]] or the memory management code in the operating system navigates the tree of page tables to find the [[page table entry]] corresponding to a virtual address.<ref>{{Cite web|url=http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0301h/I1026235.html|title=ARM Information Center|website=infocenter.arm.com|access-date=2018-04-26}}</ref><ref name="x86-software-developers-manual">{{Cite book|url=https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html|title=Intel® 64 and IA-32 Architectures Software Developer's Manual|volume=3A|publisher=[[Intel Corporation]]}}</ref>{{Rp|page=4{{hyp}}22}} This means that, in the worst case, the processor or the memory manager has to access physical memory six times for a single virtual memory access, rather than five for the previous iteration of x86-64 processors. This results in slightly reduced memory access speed.<ref name="cse-451-paging-tlbs-slides" /> In practice this cost is greatly mitigated by caches such as the [[translation lookaside buffer]] (TLB).<ref name="cse-451-paging-tlbs-slides">{{Cite web|url=https://courses.cs.washington.edu/courses/cse451/08au/lectures/10-paging_TLBs.pdf|title=CSE 451: Operating Systems: Paging & TLBs|last=Levy|first=Hank|author-link=Hank Levy (computer scientist)|date=Autumn 2008|website=[[University of Washington]]|access-date=26 April 2018}}</ref>
== References ==
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