On Thu, 2016-08-04 at 20:02 +0500, Aleem Akhtar wrote: > > I am trying to get stats of Domains running under XEN hypervisor. > I used Libvirt function for this purpose. I am trying to understand > output for Memory. Domain running is Fedora-22 with 1GB Ram. Here is my > code > > y = virDomainGetInfo(allDomain, &info); > if (y == -1) > printf("Errorl\n"); > else { > printf("Max Memory: %lu\n", info.maxMem); > printf("Memory: %lu", info.memory); > } > > I get output as > > Max Memory: 1048576 > Memory: 1048576 > > Now, as per Libvirt API, info.memory should return the memory in KBytes > used by the domain. My Question is, if info.memory returns memory used > and my domain is using complete 100% of Max Memory or not? Also I tried > to create Domain with memory varying from 128MB to 2GB with same effect. > I also tried to run some applications in Domain but Memory usage return > by given function does not change. Any help or guidance will be much > appreciated. The relevant virDomainInfo field is described as /* the memory in KBytes used by the domain */ unsigned long memory; but in this context, "used by" really means "available to". So the output above tells you that your Fedora guest has 1 GB of memory available; how much of that memory is actually being used by the guest OS is something that you can find out by running top inside the guest. -- Andrea Bolognani / Red Hat / Virtualization

On Fri, 2016-08-05 at 17:45 +0500, Aleem Akhtar wrote: > Ok. So that's why I was getting 1 GB as a result. > So is there any way I can get memory in used programmatically? > I mean without going inside guest domain. The only way I can come up with at the moment relies on qemu-guest-agent: $ virsh qemu-agent-command guest \ '{"execute": "guest-exec", "arguments": {"path": "/usr/bin/free", "capture-output": true}}' {"return":{"pid":1425}} $ virsh qemu-agent-command guest \ '{"execute": "guest-exec-status", "arguments": {"pid": 1425}}' {"return":{"exitcode":0,"out-data":"ICA...zIK","exited":true}} $ echo 'ICA...zIK' | base64 -d total used free Mem: 4020408 97244 3359560 Swap: 1048572 0 1048572 Of course you'll need to have qemu-guest-agent running inside the guest and process all the resulting information yourself. See the virDomainQemuAgentCommand() API. -- Andrea Bolognani / Red Hat / Virtualization

On Fri, 2016-08-05 at 18:49 +0500, Aleem Akhtar wrote: > Thanks. > But I am using XEN. I see. qemu-guest-agent is definitely not an option then. > And I also don't want to go inside guest. I mean I want to > get memory usage at the same level I am getting max memory > and total memory. The problem with that is that the host OS has zero knowledge of how the guest OS is using the memory it's been assigned.

> I have another question. If Memory attribute of GetDomainInfo > gives total memory I.e. memory in use plus remaining memory > than what is the use of Max Memory? You can configure your guest like   <memory unit='KiB'>4194304</memory>   <currentMemory unit='KiB'>2097152</currentMemory> Doing so would give you 2 GB of initial memory and the ability to increase that up to 4 GB at runtime. So in the virDomainInfo structure, maxMem corresponds to <memory> and memory corresponds to <currentMemory>. Confusing, I know :) > I also programmatically updated Memory using libvirt function > I.e. 1GB to 512mb. When tried to get domain statistics again > I got Max Memory 512mb and Memory 1GB.  > How is this possible? You mean memory = 512 MB and maxMem = 1 GB, right? PS: This whole thread would have been more suitable for the     libvirt-users mailing list - libvir-devel is targeted at     the development of libvirt itself. Not a big deal, but     maybe keep that in mind the next time :) --  Andrea Bolognani / Red Hat / Virtualization -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list