topic Re: SLES 10 using 400 MB swap continuously - why ? in Operating System - Linux

SLES 10 using 400 MB swap continuously - why ?

Maaz — Mon, 14 Jul 2008 02:59:52 GMT

OS: SLES 10 SP2 x86_64
DB: Oracle 10g R2
ERP: SAP

no performance issue, machine and the services response are fine, but this machine is continuously using swap. why .. from the output of "free -m" its clear that almost 5.5GB of physical memory is available as cached? then why system is using swap(almost 400 MB).

please find the attached file

Regards

Re: SLES 10 using 400 MB swap continuously - why ?

Jeeshan — Mon, 14 Jul 2008 03:25:16 GMT

This is not actually a big problem.

Look at the percentage. the 400 MB is a little part from 16GB.

Or may be coz of your application requierement of swap utilization.

Re: SLES 10 using 400 MB swap continuously - why ?

Maaz — Mon, 14 Jul 2008 06:53:40 GMT

thanks ahsan for reply/help.

I have two other SLES 10 SP2 boxes with 4 GB of physical memory runnig MySQL(5.x)... and under full load/peak times ... I have never found swap usage beyond 40 MB on those machines.
and one more thing .. when the those(MySQL) system uses swap, I found little or no memory left as "cached" and/or "free" in the output of "free -m"... and this makes sense.. i.e when no physical memory is available(either as cache and or free) then system starts swaping.

but these (SLES 10 SP2 x86_64+Oracle 10g R2+SAP) boxes are doing swap, even when there is lots of physical memory(5 GB cached) available

Re: SLES 10 using 400 MB swap continuously - why ?

Jeeshan — Mon, 14 Jul 2008 07:36:27 GMT

well Maaz

i had mentioned it earlier. The swap memory is depend upon your application design, requirement or greedyness.

Re: SLES 10 using 400 MB swap continuously - why ?

Maaz — Mon, 21 Jul 2008 03:49:37 GMT

>The swap memory is depend upon your application design,> requirement or greedyness.

I think you are right, because I also tried the following but the situation remained the same.
# cat /proc/sys/vm/swappiness
60

# echo 40 > /proc/sys/vm/swappiness
# cat /proc/sys/vm/swappiness
40

as this is a production server thats why i didnt reboot the machine after reducing the swappiness.

you know more interesting is that now the swap has reached 720 MB

Re: SLES 10 using 400 MB swap continuously - why ?

Jeeshan — Mon, 21 Jul 2008 04:15:39 GMT

you can assure a downtime atleast in a month to clear up buffers/swap and reset this server.

this will refresh the system.

Re: SLES 10 using 400 MB swap continuously - why ?

Maaz — Tue, 22 Jul 2008 04:01:43 GMT

Salam ahsan
>you can assure a downtime atleast in a month to clear up buffers/swap and >reset this server.
>this will refresh the system.
Don't you think that Linux is smart enough that no reboot is required even after running 5 months ?
I think this is MS Windows that requires a reboot(in a month) to clear up buffers/swap and reset the server.

Anyhow thanks a lot for the help/feedback.

Regards

Re: SLES 10 using 400 MB swap continuously - why ?

Jeeshan — Tue, 22 Jul 2008 04:50:41 GMT

Walaikum as-salam

Things are like that, I have seen in my experience like this kind of applications, which uses much resource. But after reboot it performs very well.

The reason behind is more or less depend to poor coding of applications or processes.