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Top Forums UNIX for Advanced & Expert Users Please advise good source of info about swapping Post 302614419 by Corona688 on Wednesday 28th of March 2012 12:58:05 PM
Old 03-28-2012
It doesn't make swap necessary. Virtual memory makes swap possible because the OS can leave triggers for itself when certain memory is used, i.e. automatically pausing a process and sending a request to the OS when the process attempts to access a swapped-out page. The ability to flag and reorder memory as you please makes other things possible too, like read-only memory, shared memory, and mapped files...

Whether swap is necessary and how much depends on the UNIX. The behavior when the system runs out of memory also depends on the UNIX.

I don't agree that no swap is advisable. Swap is your safety buffer. And depending on how you configure it, may not be that slow either. If you put it on the same spindle as your applications it'll naturally be slow...
 

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SWAPON(2)							System Calls Manual							 SWAPON(2)

NAME
swapon - add a swap device for interleaved paging/swapping SYNOPSIS
swapon(special) char *special; DESCRIPTION
Swapon makes the block device special available to the system for allocation for paging and swapping. The names of potentially available devices are known to the system and defined at system configuration time. The size of the swap area on special is calculated at the time the device is first made available for swapping. RETURN VALUE
If an error has occurred, a value of -1 is returned and errno is set to indicate the error. ERRORS
Swapon succeeds unless: [ENOTDIR] A component of the path prefix is not a directory. [EINVAL] The pathname contains a character with the high-order bit set. [ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters. [ENOENT] The named device does not exist. [EACCES] Search permission is denied for a component of the path prefix. [ELOOP] Too many symbolic links were encountered in translating the pathname. [EPERM] The caller is not the super-user. [ENOTBLK] Special is not a block device. [EBUSY] The device specified by special has already been made available for swapping [EINVAL] The device configured by special was not configured into the system as a swap device. [ENXIO] The major device number of special is out of range (this indicates no device driver exists for the associated hardware). [EIO] An I/O error occurred while opening the swap device. [EFAULT] Special points outside the process's allocated address space. SEE ALSO
swapon(8), config(8) BUGS
There is no way to stop swapping on a disk so that the pack may be dismounted. This call will be upgraded in future versions of the system. 4th Berkeley Distribution March 9, 1986 SWAPON(2)
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