Chapter Summary

   

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Swap space is a disk area that is used to temporarily store memory pages if the demand for physical memory on the system increases beyond what is installed. Out of the total installed physical memory, some is used by kernel code and data structures. The remaining memory is available for other processes. If a process demands more memory, some of the pages that are not currently in use are swapped out to the disk swap area. Two daemons known as swapper and vhand are used for memory management. If you use a complete disk or logical volume for the swap area, it is called a device swap. If you are using some of a file system for the swap and the rest of it for ordinary files, it is called file system swap. Device swap is faster, whereas file system swap is more flexible. At least one primary swap area must be available to the system during the startup process. Usually some space on the boot disk is used for the primary swap.

Swap space may be created using the swapon command or SAM. The swapon command accepts options used to set the priority of the swap space. To activate swap space at boot time, place swap space entries in the /etc/fstab file. Swap performance can be greatly affected depending on the priorities used with different swap devices.

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