iAPX 286 Operating System Writers Guide 1983

VIRTUAL MEMORYat once. It then becomes possible to allocate swap space for these segments in such a way as to minimizeseek time. Such a policy works well with the full-task fetch policy outlined previously.THRASHINGIf not carefully controlled, the I/O traffic in support of virtual memory may degrade system performancebeyond acceptable limits. The worst case of performance degradation is called thrashing. Thishappens when RAM is committed to simulating an excessively large virtual-memory space and thebehavior of the tasks in that space is such that no task can run without causing a not-present fault.You can avoid thrashing by measuring or estimating the minimum amount of RAM a task needs inwhich to operate without causing frequent not-present faults. If the task loader knows this figure, itcan refuse to load a task when not enough RAM is available. You can measure a task's RAM requirementswith a profiler such as that described previously.9-8 121960-001