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Thread: xen installed, I have got 1.8GB out of 11GB memory

  1. #1

    Default xen installed, I have got 1.8GB out of 11GB memory

    I have just installed xen server and xen tools, I reboot the system and boot is very slow, when I log in my session it takes a lot of time and HDD led is blinking non-stop. I open a text console and do a free -h and it report having 1.8GB of memmory, when I have 11GB. I have to do a reboot, use the no-xen kernel and I have again 11GB.

    I'm reading the docs but I can't see why is this happenning

    any clues?

    thanks

  2. #2
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    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    For starters, did you install your xen using the YaST virtualization module?
    You should do so, to install xen, libvirt, optionally configure a br0 network bridge device (recommend accept) and start with a known good configuration

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    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by fperal View Post
    I open a text console
    You mean you are running graphical desktop in dom0?
    I'm reading the docs but I can't see why is this happenning
    You see memory allocated to dom0 VM. The rest of memory is available to other virtual machines.

    Do you know what Xen is? What is the reason you installed it?

  4. #4

    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by tsu2 View Post
    For starters, did you install your xen using the YaST virtualization module?
    You should do so, to install xen, libvirt, optionally configure a br0 network bridge device (recommend accept) and start with a known good configuration

    TSU
    yes, I installed xen, libvirt and when asked I configured the br0

  5. #5

    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by arvidjaar View Post
    You mean you are running graphical desktop in dom0?

    You see memory allocated to dom0 VM. The rest of memory is available to other virtual machines.
    As I was using a no-xen environment with graphical desktop and I installed Xen from it, yes. I thought that I will have all the memory for the "main" VM unles I was using other VMs.

    Do you know what Xen is? What is the reason you installed it?
    Yes.
    I installed it because I use some vmware VMs and I want to test if the performance of VMs using XEN is significantly better than using vmware

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    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by fperal View Post
    I thought that I will have all the memory for the "main" VM unles I was using other VMs.
    As with any other hypervisors, every VM gets assigned fixed amount of memory. dom0 is just another (although privileged) VM. Note that dom0 is responsible for processing all IO from all other guests, which means it should not have any workload that is unrelated to that. You do not really do daily work in dom0, you create domU for that.

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    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by arvidjaar View Post
    As with any other hypervisors, every VM gets assigned fixed amount of memory. dom0 is just another (although privileged) VM. Note that dom0 is responsible for processing all IO from all other guests, which means it should not have any workload that is unrelated to that. You do not really do daily work in dom0, you create domU for that.
    Actually, only partially true, static memory is allocated by default but the System Administrator doesn't have to stop there.
    Like practically all other virtualization technologies, Xen supports dynamically allocating memory to vms, often automatically "on demand."

    Specifically relating to Xen,
    https://docs.citrix.com/en-us/xencen...dmc-about.html
    https://citeseerx.ist.psu.edu/viewdo...=rep1&type=pdf

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  8. #8

    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by tsu2 View Post
    Actually, only partially true, static memory is allocated by default but the System Administrator doesn't have to stop there.
    Like practically all other virtualization technologies, Xen supports dynamically allocating memory to vms, often automatically "on demand."

    Specifically relating to Xen,
    https://docs.citrix.com/en-us/xencen...dmc-about.html
    https://citeseerx.ist.psu.edu/viewdo...=rep1&type=pdf

    TSU
    This is the way that I was thinking that it will work.


    Quote Originally Posted by arvidjaar View Post
    Note that dom0 is responsible for processing all IO from all other guests, which means it should not have any workload that is unrelated to that. You do not really do daily work in dom0, you create domU for that.

    I have a "normal installation" of opensuse (with KDE, etc)on bare metal, when I installed Xen and boots with the kernel with xen The system boots with my installation in the dom0. What I was thinkig of was using this opensuse in dom0 and installing other machines in domu but you say I should not do that, so I have some questions

    * Why I should not use dom0 for my opensuse-KDE? It will have effects over the performance of machines in domU? or there are other problems?

    * If I have to move my opensuse-KDE to domU, I have to make a migration as if migrating from bare metal mchine to VM? or is there other way to do it?


    best regards

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    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by fperal View Post
    This is the way that I was thinking that it will work.





    I have a "normal installation" of opensuse (with KDE, etc)on bare metal, when I installed Xen and boots with the kernel with xen The system boots with my installation in the dom0. What I was thinkig of was using this opensuse in dom0 and installing other machines in domu but you say I should not do that, so I have some questions

    * Why I should not use dom0 for my opensuse-KDE? It will have effects over the performance of machines in domU? or there are other problems?

    * If I have to move my opensuse-KDE to domU, I have to make a migration as if migrating from bare metal mchine to VM? or is there other way to do it?


    best regards
    Others may have their own opinions, but IMO Dom0 should be kept lean and uncomplicated.
    Only install system essentials.

    Your commonly used installs with all the extras you might want should be installed in DomU machines.

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    Default Re: xen installed, I have got 1.8GB out of 11GB memory

    Quote Originally Posted by fperal View Post
    This is the way that I was thinking that it will work.
    Do not confuse VM virtual memory and host physical memory. These URLs talk about allocating host physical memory to VM. What you see inside VM is virtual memory configured for this VM.
    Why I should not use dom0 for my opensuse-KDE? It will have effects over the performance of machines in domU?
    Resources consumed by anything running in dom0 won't be available to handle domU requests. You said the reason to install Xen was performance. It is just logical to minimize possible performance impact on domU by reducing load in dom0.

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