long term scheduling
Posted Aug 6, 2004 3:05 UTC (Fri) by giraffedata
Parent article: Token-based thrashing control
Much older operating systems do a similar thing, but simpler, called long term scheduling. Above the regular CPU dispatch queue, you have a list of processes waiting to get into the dispatch queue. While a time slice on the CPU might be .1 second, a time slice in the dispatch queue might be 5 seconds. You don't let the dispatch queue ever contain so many processes that their working sets won't all fit in memory at the same time.
So a process gets into the inner circle, quickly faults in his working set, gets a lot of work done against that memory across many CPU time slices, then steps out and his page frames get quickly stolen by the next guy.
The fact that a process can spend a long time waiting in the outer circle is just recognition of the fact that you can't get blood from a stone. If you want an interactive system, you have to have enough memory for everyone.
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