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Top Forums UNIX for Advanced & Expert Users virtual memory management, swapping paging Post 302081616 by phrazz on Wednesday 26th of July 2006 02:02:10 PM
Old 07-26-2006
swapping vs paging

paging is managing RAM data by pages (nK chunks, called page size), swapping stores it temporarily on disk if it's not needed right away to extend physical memory through a technique called virtual memory management (VM). When the kernel moves data between RAM <-> CPU that is paging, and data moved between RAM <-> DISK is swapping.

[Actually, the memory management is usu. handled but a subprocessor component called the MMU, but for practical purposes, let's just say it's in the CPU package deal. Smilie ]

Specific flavors of UNIX use slightly different techniques and tuning. Getting down to the nitty gritty is kernel tuning, which is one of the Black Arts of UNIX. For Solaris specifics, see Adrian Cockroft's book "Sun Performance and Tuning" (slightly outdated, but is considered the "bible" on Solaris tuning).

-Phrazz

See more here: Paging (Wiki)
 

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swapon(2)							System Calls Manual							 swapon(2)

NAME
swapon - Adds a swap device for interleaved paging and swapping SYNOPSIS
swapon( char *path, int flags, int lowat, int hiwat ); PARAMETERS
Specifies the block special device to be made available. Specifies a flag. Only the MS_PREFER flag is currently supported, and it causes the specified path to be the preferred paging device. (Ignored on Tru64 UNIX.) Specifies the low water mark. (Ignored on Tru64 UNIX.) Specifies the high water mark. (Ignored on Tru64 UNIX.) DESCRIPTION
The swapon() function makes a block special device available to the system for allocation of paging and swapping space. (The operating system does not currently support paging and swapping to a normal file. All swapping and pages areas must be block special devices.) The calling process must have superuser privilege to call the swapon() function. RETURN VALUES
Upon successful completion, the swapon() function returns a value of 0 (zero). If an error has occurred, -1 is returned and errno is set to indicate the error. ERRORS
If the swapon() function fails, errno may be set to one of the following values: A component of the path prefix is not a directory. The pathname contains a character with the high-order bit set, the device was not specified, the device configured by the path parameter was not configured into the system as a swap device, or the device does not allow paging. A component of a pathname exceeded NAME_MAX charac- ters, or an entire pathname exceeded PATH_MAX characters. The named device does not exist. Search permission is denied for a component of the path prefix. Too many symbolic links were encountered in translating the pathname. The caller does not have appropriate privilege. The device specified by the path parameter has already been made available for swapping. The major device number of the path parameter is out of range (this indicates no device driver exists for the associated hardware). An I/O error occurred while opening the swap device. The path parameter points outside the process' allocated address space. An attempt was made to activate a paging file on a read-only file system. RELATED INFORMATION
Commands: swapon(8), config(8) delim off swapon(2)
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