Abstract
This chapter reviews some basic swapper concepts. The swapper process is the system wide physical memory manager. Its responsibilities include maintaining an adequate supply of physical memory and ensuring that the highest priority computable kernel threads are resident in memory. The swapper maintains the number of free pages above the threshold established by the SYSGEN parameter FREELIM. The swapper stops reclaiming pages when the number of free pages exceeds the SYSGEN parameter FREEGOAL. The swapper ensures that there are fewer pages on the modified page list than the threshold established by the SYSGEN parameter MPW_HILIMIT. When the modified page list grows above this limit, the swapper calls the modified page writer routine to write the contents of some modified pages to their backing store and to move the physical pages to the free page list. The swapper spends its idle time hibernating. Executive components that detect a need for swapper activity wake the swapper by calling routine SCH$SWPWAKE, in module RSE. The swapper is implemented as a separate process whose single kernel thread has a priority of 16, the lowest real-time priority. It is selected for execution like any other kernel thread in the system. The swapper serves as a convenient process context for several system functions.
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