[Users] Memory usage

[René Koch]

On Wed, 2014-02-12 at 11:22 -0500, Doron Fediuck wrote:
> 
> ----- 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.


Thanks a lot for the information.


> 
> 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.


I just had a look at the bugzilla report and the RHEV documentation
which says "Current memory in bytes used by the virtual machine.".
So this means, the reported values are totally useless for monitoring
memory usage of a virtual machine if KSM is active. I would expect to
get the memory usage of a virtual machine and not how much memory is
consumed on the hypervisor (this is pretty useless information for me).

Is it planned to report the memory usage in a virtual machine in the API
as well?


Regards,
René


> 
> Doron
> 
> P.S.
> René- thanks for helping!