Use Bit Scanning in Replacement Decisions

• Published in: IEEE transactions on computers Vol. C-28; no. 2; pp. 133 - 141
• Main Authors: Easton, Franaszek
• Format: Journal Article
• Language: English
• Published: IEEE 01.02.1979
• Subjects: Miss ratio; operating system overhead; page fault rate; page replacement algorithms; paged memories; paged storage
• ISSN: 0018-9340; 1557-9956
• DOI: 10.1109/TC.1979.1675302

In paged storage systems, page replacement policies generally depend on a use bit for each page frame. The use bit is automatically turned on when the resident page is referenced. Typically, a page is considered eligible for replacement if its use bit has been scanned and found to be off on µ consecutive occasions, where µ is a parameter of the algorithm. This investigation focuses on the dependence of the number of bit-scanning operations on the value of µ and on properties of the string of page references. The number of such operations is a measure of the system overhead incurred while making replacement decisions. In particular, for several algorithms, the number of scans per reference is shown to be approximately proportional to µ However, empirical results from single-program traces show that the value of µ has little effect on the miss ratio. Although the miss ratios for the bit-scanning algorithms are close to those of least recently used (LRU), it is pointed out that increasing the value of µ need not bring the bit-scanning policies closer to LRU management.