Guardian User's Guide

Performing Routine Disk Operations
Guardian User’s Guide—425266-001
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How Kernel-Managed Swap Files Affect You
reservation. When a process no longer needs swap space, the NonStop™ Kernel returns
it to KMSF.
Components of Kernel-Managed Swapping
Kernel-managed swapping is implemented through:
•
The Kernel-Managed Swap Facility (KMSF), which reads the kernel-managed swap
configuration file, controls the swap files and provides, resizes, and receives back
swap space reservations and swap space allocations.
•
The NonStop™ Kernel memory manager, which acquires, requests resizes of, and
returns swap space reservations, and requests and returns swap space allocations.
•
NSKCOM, the NonStop™ Kernel utility used to configure and manage kernel-
managed swap files.
•
ZSYSCFG, the configuration file specifying the names and usage of kernel-
managed swap files.
•
The kernel-managed swap files.
Kernel-Managed Swap Process Flow
When a process is created, the NonStop™ Kernel memory manager requests a single
swap space reservation for the process from KMSF. If there is a shortage of available
physical memory, the memory manager finds a page suitable for swapping, such as a
page belonging to an inactive process. If the chosen page contains dynamic data (rather
than code or read-only data), its contents must be saved on disk. The memory manager
requests swap space from KMSF, which finds and allocates swap space against the
reservation.
How Kernel-Managed Swap Files Affect You
KMSF, which centralizes the control of swap space under the NonStop™ Kernel, has
implications for users, operations personnel, and application developers.
KMSF and Users
When a user starts a process, KMSF provides the swap space that the process requires at
process creation. User control over certain aspects of swap files is limited, because
kernel-managed swap files provide swap space for multiple processes:
•
In most cases, users cannot decide where data will be swapped. The user can specify
the location of the swap space for extended data segments only. Otherwise, data is
swapped to whatever kernel-managed swap file or files are available for the
processor in which the process is running.
•
Only super-group users (255,n) can resize, add, or delete kernel-managed swap
files.