Re: What is eating up Swap

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Hi,

I have a smiliar problem on a CentOS 6.4 KVM host.

The host has 32 GB memory.
virt-top shows: Mem: 30208 MB (30208 MB by guests)
vm.swappiness = 0

Guests couldn't use more than 30,2 GB memory!

# uname -r
2.6.32-358.14.1.el6.x86_64

# uptime
 13:48:16 up 132 days,  1:55,  3 users,  load average: 3.10, 2.45, 1.16

# sysctl vm.swappiness
vm.swappiness = 0

# free -m
             total       used       free     shared    buffers     cached
Mem:         32081      31784        296          0        206       2635
-/+ buffers/cache:      28943       3137
Swap:        16111       3220      12891

Swap usage:

PID=1877 swapped 415092 KB (qemu-kvm)
PID=1925 swapped 47680 KB (qemu-kvm)
PID=2012 swapped 37188 KB (qemu-kvm)
PID=2114 swapped 555560 KB (qemu-kvm)
PID=2154 swapped 191832 KB (qemu-kvm)
PID=5299 swapped 341108 KB (qemu-kvm)
PID=11564 swapped 327620 KB (qemu-kvm)
PID=15383 swapped 218360 KB (qemu-kvm)
PID=16299 swapped 11280 KB (qemu-kvm)
PID=20391 swapped 946656 KB (qemu-kvm)
PID=30963 swapped 23040 KB (qemu-kvm)
PID=31248 swapped 169680 KB (qemu-kvm)
Overall swap used: 3285096 KB

What's going wrong? vm.swappiness ist set to 0 and the system has enough
free memory without need of swapping?

--
Chris






2013/12/12 Devin Reade <gdr@xxxxxxx>

> --On Tuesday, December 10, 2013 08:18:09 AM -0800 John R Pierce
> <pierce@xxxxxxxxxxxx> wrote:
>
> > during idle time, dirty pages will be written to swap so they can then
> > be discarded if needed.   ignore it, it means nothing
>
> Agreed.  If you want to see if paging is actually an issue,
> run "vmstat -5" and ignore the first line of output.  If, over time,
> you're seeing consistently high values for the si and so columns,
> then you have something to investigate.  If they're usually
> low or zero, then ignore your swap usage.
>
> Same thing goes for the "free" values in top and vmstat; having
> low free memory counts in a long running kernel is normal and
> can be ignored.  (Too many people, especially coming from the
> windows world, get wrapped around the handle about this.)
>
> If you want to maintain a historical record of memory and other
> performance indicators that you can use for investigative purposes
> after the fact, see the man page for sar(1).
>
> Devin
>
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