[libvirt] libvirt memory flags

Narayanan, Krishnaprasad narayana at uni-mainz.de
Fri Jan 2 15:36:19 UTC 2015

Hi Martin,

Thanks for your reply.  Please correct me if I am wrong here. 

The latest version of libvirt generates the following flags with respect to memory
a) swap_in
b) swap_out
c) major_fault
d) minor_fault
e) unused
f) available
g) actual_balloon
h) rss

I assumed that the "unused" flag represents the memory that is not consumed / not used by the virtual machine. In order to calculate the memory that is used by the VM / KVM process associated with the VM, I thought I should subtract the available or set memory - unused memory.


-----Original Message-----
From: Martin Kletzander [mailto:mkletzan at redhat.com] 
Sent: Freitag, 2. Januar 2015 16:15
To: Narayanan, Krishnaprasad
Cc: libvir-list at redhat.com
Subject: Re: [libvirt] libvirt memory flags

On Wed, Dec 31, 2014 at 01:36:21AM +0000, Narayanan, Krishnaprasad wrote:
>Hallo all,
>I am using libvirt version 1.1.1 on one of the nodes which has several VMs. When I executed the command,  virsh dommemstat <domain UUID>, I am getting the following flags as output: actual, swap_in and rss. The API does not return "unused memory" flag that is associated to the virtual machine / domain.

It's hard to define what you mean by "unused" memory.  The API you are talking about returns (at least for the QEMU driver) memory information about the process itself.  These are, of course, different values than he amount of memory inside the VM.  If you want to know what is the current memory amount set for the VM, you can find it in the XML output of 'virsh dumpxml <domain>'.  Further data should be available from guest agent, but libvirt does not have an API for this.  You can, however, query that information using an arbitrary guest agent command (virsh qemu-agent-command), but I'm not sure about that and neither about the commands.


>Can I kindly know is there a documentation that describes different memory flags? Further, can I get help from the forum to obtain information about the unused memory associated with the virtual machine / domain?

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