[CentOS] swapping on centos 5.1

Fri Feb 1 09:49:10 UTC 2008
Luke Dudney <listmail at lukedudney.com>

On 01/02/2008 01:53, Jerry Geis wrote:
> Hi all,
>
> I used to use centos 4.5 on an AMD 4800+ with 2GIG ram.
> Now I use centos 5.1 on AMD 6400+ with 4GIG RAM.
>
> The system responsiveness is different between the two.
> I noticed that centos 5.1 seems to be swapping programs out
> of memory at times resulting in slowness (perceived by me).
>
> I played with swappiness (/proc/sys/vm/) setting to 10, then 1 then 0.
> Still resulted in the same perceived slowness.
> Today I did swapoff -a and now the system obviously does not swap
> anything out all all. I thought thats what swappiness of 0 would have 
> done.
>
> Are others experiencing this also? The perceived slowness maks the older
> system with less RAM and slower CPU "seem" faster.
>
> Any suggestions on other things to try?
>
> Jerry

Large amounts of swap "in use" does not necessarily reflect a system 
that is swapping heavily, and your perceived slowness may have another 
cause.

Take a look at the output of "vmstat 10" command's swap columns for real 
time or "sar -W" for historical information regarding the number of 
pages being swapped in and out. These numbers will give you a much more 
accurate picture of how much swapping is occuring on your system.

Cheers
Luke