2.7.2 Nonresident Memory
Memory may be resident or nonresident.
When nonresident memory is accessed, data is copied to that memory from a disk or other storage. It
therefore requires complicated processing such as disk access by a device driver.
Accordingly, when nonresident memory is accessed, the device driver, etc., must be in operational state.
Access is not possible during dispatch disabled or interrupts disabled state, or while a task-independent portion is executing.
Similarly, in OS internal processing, it is necessary to avoid accessing nonresident memory in a critical section. One such case would be when the memory address passed in a system call parameter points to nonresident memory. Whether or not system call parameters are allowed to indicate nonresident memory is an implementation-dependent matter.
Data transfer from a disk or the like due to nonresident memory access is not performed by T-Kernel.
Normally T-Kernel is used along with subsystems that handle virtual memory management and other such processing.
In a system that does not use virtual memory, system call parameters or the like pointing to nonresident memory can be ignored, treating all memory as resident.
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