Kernel-Managed Swap Facility (KMSF) Manual

Kernel-Managed Swap Facility (KMSF) Manual—425824-005
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1 Introduction
The Kernel-Managed Swap Facility (KMSF) and its related components manage virtual
memory for processes.
Virtual Memory
Modern operating systems have two kinds of memory:
•
Physical memory, which is memory contained on memory board or processor and
memory board.
•
Virtual memory, which is memory temporarily stored in disk files called swap files.
When all physical memory has been allocated and more memory is needed, pages of
memory that are not in use are written to disk and are read back to physical memory
when the data is accessed by the process.
Because the physical memory is fully allocated when virtual memory is used, pages of
memory that are not being used must be written to disk in order to make room for
pages of memory that must be accessed by the process. Memory pages are swapped
between physical memory and disk files. These disk files are called swap files.
Virtual Memory In NonStop Systems
In NonStop systems virtual memory is managed two ways:
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Using conventional swap files
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Using the KMSF and KMS files
Conventional Swap Files
Conventional swap files:
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Are defined by the calling process instead of by the system
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Are dedicated to the calling process
•
Must be opened and closed each time a process is created and deleted
Topic Page
Virtual Memory
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Virtual Memory In NonStop Systems 1-1
Components of Managing Virtual Memory Using KMSF 1-3
Kernel-Managed Swap Space Process Flow 1-5
Characteristics of KMS Files 1-7
KMS Files and New Systems 1-10