Design and performance of future virtual memory systems using fast secondary storage
Kern Koh · 1981
Much of the earlier work on virtual memory system was conducted on the basis of a machine which used rotational storage devices, such as drum or disk, as secondary storage devices. The speed ratio between a typical MOS memory and drum is on the order of 10('4) to 10('5). Continued effort in memory technology is expected to provide cheaper and faster memory in the not-too-distant future as a candidate for replacing slow rotational storage devices. Such new technology should be expected to require changes in the design of virtual memory systems. In this thesis, new memory technologies are surveyed and their implications for the design and performance of paged virtual memory systems is studied. The work is divided into several phases. First, we investigate the effect of varying the page size on the behavior of page reference string. This result is then used to develop a new methodology of choosing optimal page size. This method is based on a direct measurement of spacetime product for each page size. Next, we explore the effect of changing secondary storage on the design of memory management policies. Our study indicates that a drastic change in the supporting hardware characteristics may require major changes in the design of memory policies. A new memory policy, called Adaptive Policy, is developed and its performance is compared with that of the working set policy. A major advantage of this new policy is that its performance is quite insensitive to the choice of the parameter value. Lastly, a new analytic lifetime function is developed. Several analytic lifetime functions have been proposed in the past but they were either a poor match with real lifetime functions or they only fitted a partial segment of real lifetime function. The new lifetime function overcomes these two deficiencies and should be a valuable tool in future performances study of computing system. This work is intended as a useful guidance for studies and design of future virtual memory systems using a high speed secondary storage.