[Users] Memory usage

[Doron Fediuck]

----- Original Message -----
> From: "René Koch" <rkoch at linuxland.at>
> To: "Koen Vanoppen" <vanoppen.koen at gmail.com>
> Cc: users at ovirt.org
> Sent: Wednesday, February 12, 2014 4:18:37 PM
> Subject: Re: [Users] Memory usage
> 
> On Wed, 2014-02-12 at 15:14 +0100, Koen Vanoppen wrote:
> > In The GUI, it says it's using 25% of the memory.
> 
> 
> I guess it's the real value, right?
> The same happened for the memcached vm, someone reported to me -
> negative value in REST-API, but correct graph in oVirt webadmin GUI.
> 
> I fear I have no idea how this can happen - so maybe someone else can
> help you troubleshoot this issue.
> > 
> > 
> > 
> > 2014-02-12 15:10 GMT+01:00 Koen Vanoppen <vanoppen.koen at gmail.com>:
> >         Thanks for the quick respons, but there is no memcached
> >         running on that VM.
> >         
> >         
> >         Kind regards
> >         
> >         
> >         
> >         2014-02-12 15:06 GMT+01:00 René Koch <rkoch at linuxland.at>:
> >         
> >                 On Wed, 2014-02-12 at 14:55 +0100, Koen Vanoppen
> >                 wrote:
> >                 > Dear all,
> >                 >
> >                 >
> >                 > When we monitor one of our machines, we noticed that
> >                 there was one vm
> >                 > that was constantly giving a error of memory usage.
> >                 But when we took a
> >                 > look at it, there is actually nothing wrong with it.
> >                 Now we looked
> >                 > furhter then that. We looked at the API of the
> >                 machine and noticed
> >                 > something very strange:
> >                 >
> >                 > <statistic
> >                 >
> >                 href="/api/vms/3b9aa245-75ff-42e8-b921-1c9ce61826bf/statistics/b7499508-c1c3-32f0-8174-c1783e57bb08"
> >                 id="b7499508-c1c3-32f0-8174-c1783e57bb08"><name>memory.used</name><description>Memory
> >                 used (agent)</description><values
> >                 type="INTEGER"><value><datum>-944892806</datum></value></values><type>GAUGE</type><unit>BYTES</unit>
> >                 >
> >                 >
> >                 > It's a negative...
> >                 
> >                 
> >                 
> >                 Do you have memcached running in this vm?
> >                 
> >                 I heard about this issue with memcached, but never
> >                 tested memcached in
> >                 my oVirt environment. You get the real usage value
> >                 with
> >                 memory.used = memory.installed + memory.used
> >                 
> >                 
> >                 Regards,
> >                 René
> >                 
> >                 >
> >                 >
> >                 > What could be the problem?
> >                 >
> >                 >
> >                 > Kind regards,
> >                 >
> >                 > koen
> >                 >
> >                 

Guys,
these values are usually a result of overcommitment mechanism usage.
For example, if KSM is effective, it will free a lot of memory pages,
and total-free-committed becomes negative.

This was reported in https://bugzilla.redhat.com/show_bug.cgi?id=977758
and the engine is using memFree reported by vdsm, which is more accurate.

The API reports the old version due to backwards compatibility.

Doron

P.S.
René- thanks for helping!