swapd(8)

NAME

swapd - dynamic swapping manager

SYNOPSIS

swapd  [-h]   [--help]   [--copyright]   [--config   file]
[--maxswaps  n]  [--memlimit  kb]  [--mkswap path] [--pause msec]
[--pidfile file] [--swapdir dir] [--swapsize kb] [--timeout sec]

DESCRIPTION

swapd is a dynamic swapping manager. It provides the sys

tem with as much swap space (virtual memory) as is required at a

particular time by dynamicly creating swap files. This is more

convinient than using fixed swap files and/or partitions because

they (a) are unused most of the time and are just taking up disk

space; and (b) provide a limited amount of virtual memory.

OPTIONS

All values given on the command line will override config

file values.

-h, --help Displays the command line help.

--copyright Displays the copyright notice.

--config file Location of an alternate configuration

file.

--maxswaps n Maximum number of swap files. No more than

n swap files will be used. The default is 8 (as many as the de

fault kernel will allow).

--memlimit kb Memory limit in kilobytes. When the total

amount of free memory gets below this number, swapd creates a new

swap file.

--mkswap path Location of mkswap(8), usually /sbin/mk

swap.

--pause msec Pause between memory checks in miliseconds

(when the total amount of free memory is above memlimit).

--pidfile file Location of the PID file, usually

/var/run/swapd.pid.

--swapdir dir Swap directory where all the swap files

are kept.

--swapsize kb Swap file size (>=64k).

--timeout sec Timeout. If the last created swap file is

unused for sec seconds, it will be removed. The last created

swapfile is considered unused when there are more than memlimit +

swapsize kb of free memory (physical + swap).

CONFIGURATION

This is an example configuration file:

# swapd.conf - config file for swapd
#
# Copyright 2000 Neven Lovric <nlovric@jagor.srce.hr>
#

# Memory limit in kilobytes.
# When the total amount of free memory gets below this

number, swapd creates
# a new swap file.
# 16384 or more recommended
memlimit 16384

# Pause between memory checks in miliseconds.
# When the total amount of free memory is above <memlim

it>, swapd will pause
# for <pause> miliseconds before checking memory again.
# 1000 should be ok for most systems
pause 1000

# Swap file size in kilobytes.
# >= 64, 4096 recommended
swapsize 4096

# Maximum number of swap files.
# No more than <maxswaps> swap files will be used.
# 0 = unlimited (as many as the kernel will allow)
# 8 = how many a default kernel allows
maxswaps 8

# Timeout in seconds.
# If the last created swap file is unused for <sec> sec

onds, it will be
# removed. The last created swapfile is considered unused

when there are
# more than <memlimit> + <swapsize> kb of free memory

(physical + swap).
# 60 is nice
timeout 60

# Swap directory where all the swap files are kept.
swapdir /swap

# PID file (where the currently running swapd stores it's

PID so a new swapd
# can find it)
pidfile /var/run/swapd.pid

# Full path to mkswap.
mkswap /sbin/mkswap

PERFORMANCE

The most important parameter which may drasticly effect

performance is the memory limit. If the memory limit is low, (1)

there may not be enough memory ready for a program to allocate at

once or (2) swapd may not be able to create new swap files before

we run out of memory. If your programs are running out of memory,

it will primarily be due to a low memory limit. If you really

want to have a low memory limit, you should decrease the swap

size and pause.

The second important parameter is the swap size. If you

choose to use bigger swap files, you may experience slowdowns

when swap files are created. On the other hand, small swap files

may lower performance when there are many of them. The important

thing is not to make them too big to create before we run out of

memory.

Another important parameter is the pause, which should be

shorter on faster systems. If it is too long, swapd may fail to

detect rapid memory changes and therefore fail to create new swap

files when they are needed. However, if you notice swapd is con

stantly using too much CPU, increase the pause.

FILES

/etc/swapd.conf
/var/run/swapd.pid
/etc/init.d/swapd
SWAPDIR/linux*.swp

BUGS

Might fail if swapping over NFS

SEE ALSO

mkswap(8), swapon(8), swapoff(8), free(8)

MAINTAINER

Aigars Mahinovs <aigarius@debian.org>

AUTHOR

Neven Lovric <nlovric@linux.hr>

The latest upstream version is available via anonymous

ftp:

ftp://ftp.linux.hr/pub/swapd

swapd May 21, 2000

swapd(8)