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Top Forums UNIX for Advanced & Expert Users Sun: High kernel usage & very high load averages Post 98132 by rhfrommn on Monday 6th of February 2006 11:21:56 AM
Old 02-06-2006
I strongly suspect this server needs more memory. If you look at the IO Wait it is very small, meaning the I/O isn't causing problems. But the free memory is only a few percent of the total, meaning you are out of memory. The system having to move chunks of data between main memory and swap is what is driving your CPU usage through the roof. If you get more memory, it should solve the problem since that swapping can stop.

One way to verify that is to use sar -g to check how much paging activity is going on. Here is an example from my box.

krypton$ sar -g 5 5

SunOS krypton 5.10 Generic_118822-02 sun4u 02/06/2006

10:18:34 pgout/s ppgout/s pgfree/s pgscan/s %ufs_ipf
10:18:39 0.00 0.00 0.00 0.00 0.00
10:18:44 0.00 0.00 0.00 0.00 0.00
10:18:49 0.00 0.00 0.00 0.00 0.00
10:18:54 0.00 0.00 0.00 0.00 0.00
10:18:59 0.00 0.00 0.00 0.00 0.00

Average 0.00 0.00 0.00 0.00 0.00
krypton$

Krypton isn't heavily loaded and has plenty of free memory, so there is no paging or swapping going on at all. If your box shows non-zero numbers here it is out of memory and having to swap. Occasional non-zero is ok as it may just be moving old data out of memory, but if it is constantly a high number it is a problem. My guess is that is what you'll see.
 

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SWAPON(8)						     Linux Programmer's Manual							 SWAPON(8)

NAME
swapon, swapoff - enable/disable devices and files for paging and swapping SYNOPSIS
/sbin/swapon [-h -V] /sbin/swapon -a [-v] [-e] /sbin/swapon [-v] [-p priority] specialfile ... /sbin/swapon [-s] /sbin/swapoff [-h -V] /sbin/swapoff -a /sbin/swapoff specialfile ... DESCRIPTION
Swapon is used to specify devices on which paging and swapping are to take place. Calls to swapon normally occur in the system multi-user initialization file /etc/rc making all swap devices available, so that the paging and swapping activity is interleaved across several devices and files. Normally, the first form is used: -h Provide help -V Display version -s Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25. -a All devices marked as ``swap'' swap devices in /etc/fstab are made available. Devices that are already running as swap are silently skipped. -e When -a is used with swapon, -e makes swapon silently skip devices that do not exist. -p priority Specify priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel. priority is a value between 0 and 32767. See swapon(2) for a full description of swap priorities. Add pri=value to the option field of /etc/fstab for use with swapon -a. Swapoff disables swapping on the specified devices and files. When the -a flag is given, swapping is disabled on all known swap devices and files (as found in /proc/swaps or /etc/fstab). NOTE
You should not use swapon on a file with holes. Swap over NFS may not work. SEE ALSO
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8) FILES
/dev/hd?? standard paging devices /dev/sd?? standard (SCSI) paging devices /etc/fstab ascii filesystem description table HISTORY
The swapon command appeared in 4.0BSD. Linux 1.x 25 September 1995 SWAPON(8)
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