[ovirt-users] vm "maximum memory" setting questions

Tue Apr 18 10:11:52 UTC 2017

Hello michal, 

Thanks for your answers. 
If others have same questions, I did found this information below on oVirt web site (http://www.ovirt.org/develop/release-management/features/engine/maximum-memory-size/) 
Note on size of maximum memory 

If memory hot-plug is not required, max memory can be set to be the same as VM memory. Suggested value is 4x size of VM memory. Larger max memory is discouraged because: 

    * I can make QEMU process to start for longer time. 
    * If hot plugged memory is also required to be hot unpluggable, it needs to be considered as movable by the guest kernel. Kernel requires the amount of movable memory to be at most 4x larger that non-movable memory for stable run. 
    * On PowerPC platform continuous block of non-movable memory of size 1/64 of the max memory needs to be allocated for each VM. 

cordialement, regards, 

	Nelson LAMEIRAS 
Ingénieur Systèmes et Réseaux / Systems and Networks engineer 
Tel: +33 5 32 09 09 70 
nelson.lameiras at lyra-network.com 

www.lyra-network.com | www.payzen.eu 

Lyra Network, 109 rue de l'innovation, 31670 Labège, FRANCE 

From: "Michal Skrivanek" <michal.skrivanek at redhat.com> 
To: "Nelson Lameiras" <nelson.lameiras at lyra-network.com> 
Cc: "ovirt users" <users at ovirt.org> 
Sent: Tuesday, April 18, 2017 11:55:46 AM 
Subject: Re: [ovirt-users] vm "maximum memory" setting questions 

On 18 Apr 2017, at 11:46, Nelson Lameiras < nelson.lameiras at lyra-network.com > wrote: 

Hello, 

A new vm setting "maximum memory" has appeared in oVirt >4 which by default has the value "current memory”*4 

In 4.1 

BQ_BEGIN

- Why is "maximum memory" setting necessary to set? 

BQ_END

BQ_BEGIN

- Why isn't this value set to "infinity" by default ? 

BQ_END

Because it’s recommended to be about 4x the startup size by linux kernel 

BQ_BEGIN

It seems to me kind of uselessly counter productif to have to decide a maximum memory amount beforehand. if we do this, will we have to set maximum CPU cores also in the future (being devil's advocate here ;) ) 

BQ_END

You don’t have to decide, you can keep the default 4x. 
For CPUs it is not currently needed and is set according to engine-config maximum supported by qemu-kvm - 288 in 4.1 

Thanks, 
michal 
. 

BQ_BEGIN

I did searched oVirt documentation, but very little information is available. 
Maybe this is an libvirt question, but I'm hopping a oVirt guru could quickly enlighten me. 

cordialement, regards, 

<element-signature_logo_lyra_115x94.jpg> 
	Nelson LAMEIRAS 
Ingénieur Systèmes et Réseaux / Systems and Networks engineer 
Tel: +33 5 32 09 09 70 
nelson.lameiras at lyra-network.com 

www.lyra-network.com | www.payzen.eu 
<element-signature_logo_YouTube_32x28.jpg> 
	<element-signature_logo_LinkedIn_41x28.jpg> 
	<element-signature_logo_Twitter_42x28.jpg> 
	<element-signature_payzen_61x28.jpg> 

Lyra Network, 109 rue de l'innovation, 31670 Labège, FRANCE 

_______________________________________________ 
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BQ_END

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