An Operating Systems Vade Mecum

118 Space Management Chapter 3length of physical store. If there is a layer of segmentation above paging, several lineararrays of words are grouped together to make up an address space. The result is farremoved, both in form and in function, from the original material from which all theseabstractions are built.9 FURTHER READINGA good summary of virtual store techniques is given by Denning (1970). A substantialamount of research has been directed to design, modeling, simulation, and measurementof various space-management schemes. By far the greatest effort has been devoted topaging. Smith (1978) has compiled a large bibliography of the relevant literature.Belady, who showed that the Min algorithm is optimal (1966), also discovered theanomalies that FIFO can produce in the fault-rate graph (1969). An article by Masuda(1977) notices that a working set policy becomes less responsive as phase changesincrease in frequency. The value of the window size w becomes critical in these situations.Babaoglu and Joy (1981) describe how they modified a version of Unix that usedsegmentation to use swapping on the DEC VAX, which does not have a Used field. TheWSCLOCK page-replacement policy was developed by Carr and Hennessy (1981).Database management systems have atypical page-reference behavior, which can lead topoor results with standard page-replacement algorithms. This issue is introduced in exercise25. More details can be found in Stonebraker’s article (1981).Knuth (1973) gives a good review of the boundary-tag, first-fit, and best-fit storageallocation. The warning about circular first fit in large spaces was given by Shore (1975).Maintaining subpools for blocks of popular sizes has been suggested by Margolin (1971).10 EXERCISES1. In a single-segment scheme, the storage manager wants to shuffle. How should itfind which process corresponds to which busy piece of physical store?2. Design a data structure for the shared-segment table in the two-segment organization.How is the table addressed?3. You are the president of Cheapo Computronics, and your star hardware designerhas suggested a brilliant idea: Implement segmentation, but let the least significantm bits of a virtual address be used to select the segment, and let the other bitsdetermine the offset. Should the designer retire or get a raise? Why?