Re: [Qemu-devel] Fedora FC21 - Bug: 100% CPU and hangs in gettimeofday(&tp, NULL); forever

[Gerhard Wiesinger <lists@wiesinger.com>]

On 02.03.2015 10:26, Paolo Bonzini wrote:
>
> On 01/03/2015 11:36, Gerhard Wiesinger wrote:
>> So far it happened only the PostgreSQL database VM. Kernel is alive
>> (ping works well). ssh is not working.
>> console window: after entering one character at login prompt, then crashed:
>> [1438.384864] Out of memory: Kill process 10115 (pg_dump) score 112 or
>> sacrifice child
>> [1438.384990] Killed process 10115 (pg_dump) total-vm: 340548kB,
>> anon-rss: 162712kB, file-rss: 220kB
> Can you get a vmcore or at least sysrq-t output?

Yes, next time it happens I can analyze it.

I think there are 2 problems:
1.) OOM (Out of Memory) problem with the low memory settings and kernel 
settings (see below)
2.) Instability problem which might have a dependency to 1.)

What I've done so far (thanks to Andrey Korolyov for ideas and help):
a.) Updated maschine type from pc-0.15 to pc-i440fx-2.2
virsh dumpxml database | grep "<type"
     <type arch='x86_64' machine='pc-0.15'>hvm</type>

virsh edit database
virsh dumpxml database | grep "<type"
     <type arch='x86_64' machine='pc-i440fx-2.2'>hvm</type>

SMBIOS is updated therefore from 2.4 to 2.8:
dmesg|grep -i SMBIOS
[    0.000000] SMBIOS 2.8 present.
b.) Switched to tsc clock, kernel parameters: clocksource=tsc nohz=off 
highres=off
c.) Changed overcommit to 1
echo "vm.overcommit_memory = 1" > /etc/sysctl.d/overcommit.conf
d.) Tried 1 VCPU instead of 2
e.) Installed 512MB vRAM instead of 384MB
f.) Prepared for sysrq and vmcore
echo "kernel.sysrq = 1" > /etc/sysctl.d/sysrq.conf
sysctl -w kernel.sysrq=1
virsh send-key database KEY_LEFTALT KEY_SYSRQ KEY_T
virsh dump domain-name /tmp/dumpfile
g.) Further ideas, not yet done: disable memory balooning by 
blacklisting baloon driver or remove from virsh xml config

Summary:
1.) 512MB, tsc timer, 1VCPU, vm.overcommit_memory = 1: no OOM problem, 
no crash
2.) 512MB, kvm_clock, 2VCPU, vm.overcommit_memory = 1: no OOM problem, 
no crash

So the OOM problem seems to be solved (at least it didn't happen so far) 
by installing 512MB RAM and setting vm.overcommit_memory = 1 (I guess 
just setting overcommit would be fine, too).

Instability didn't occour so far. If I can't reproduce it, I'll revert 
the settings.

Ciao,
Gerhard