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@gno.org
--On Tuesday, December 10, 2013 08:18:09 AM -0800 John R Pierce pierce@hogranch.com 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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