Re: [Xen-devel] Re: [Xen-users] Max. PV and HVM Guests

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, Nov 09, 2009 at 08:01:00PM +0800, Mr. Teo En Ming (Zhang Enming) wrote:
>    No, I didn't limit dom0 memory in grub.conf.
> 

You should. 

If dom0 has all the memory at boot time, you need to balloon down dom0 
memory every time you create a new guest - this can (and will) cause 
problems with the dom0 linux kernel.

Linux calculates some internal parameters/buffers/values based on the
_boot time_ amount of memory. And when the amount of memory goes down to
only a small fraction of that while creating new guests bad things can
happen..

It still shouldn't crash though.. I bet your problem will get fixed when
you limit the dom0 memory to say dom0_mem=512M and reboot.

-- Pasi

>    Here's my xm info output after I have shutdown all the virtual machines.
> 
>    [root@fedora11-x86-64-host ~]# xm list
>    Name                                        ID   Mem VCPUs      State
>    Time(s)
>    Domain-0                                     0  2812     2     r-----
>    3242.5
>    [root@fedora11-x86-64-host ~]# xm info
>    host                   : fedora11-x86-64-host
>    release                : 2.6.30-rc3-enming.teo-tip
>    version                : #1 SMP Wed Aug 19 23:14:15 SGT 2009
>    machine                : x86_64
>    nr_cpus                : 2
>    nr_nodes               : 1
>    cores_per_socket       : 2
>    threads_per_core       : 1
>    cpu_mhz                : 2800
>    hw_caps                :
>    bfebfbff:20100800:00000000:00000140:0400e3bd:00000000:00000001:00000000
>    virt_caps              : hvm hvm_directio
>    total_memory           : 6039
>    free_memory            : 3124
>    node_to_cpu            : node0:0-1
>    node_to_memory         : node0:3124
>    xen_major              : 3
>    xen_minor              : 5
>    xen_extra              : -unstable
>    xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32
>    hvm-3.0-x86_32p hvm-3.0-x86_64
>    xen_scheduler          : credit
>    xen_pagesize           : 4096
>    platform_params        : virt_start=0xffff800000000000
>    xen_changeset          : Tue Sep 01 11:34:31 2009 +0100 20143:a7de5bd776ca
>    xen_commandline        : iommu=1
>    cc_compiler            : gcc version 4.4.1 20090725 (Red Hat 4.4.1-2)
>    (GCC)
>    cc_compile_by          : root
>    cc_compile_domain      : (none)
>    cc_compile_date        : Thu Sep 10 07:01:13 SGT 2009
>    xend_config_format     : 4
> 
>    --
>    Mr. Teo En Ming (Zhang Enming) Dip(Mechatronics) BEng(Hons)(Mechanical
>    Engineering)
>    Alma Maters:
>    (1) Singapore Polytechnic
>    (2) National University of Singapore
>    My Primary Blog: [1]http://teo-en-ming-aka-zhang-enming.blogspot.com
>    My Secondary Blog: [2]http://enmingteo.wordpress.com
>    My Youtube videos: [3]http://www.youtube.com/user/enmingteo
>    Email: [4]space.time.universe@xxxxxxxxx
>    Mobile Phone (Starhub Prepaid): +65-8369-2618
>    Street: Bedok Reservoir Road
>    Country: Singapore
> 
>    On Mon, Nov 9, 2009 at 7:54 PM, Pasi Kärkkäinen <[5]pasik@xxxxxx> wrote:
> 
>      On Mon, Nov 09, 2009 at 06:52:37PM +0800, Mr. Teo En Ming (Zhang Enming)
>      wrote:
>      >    Hi,
>      >
>      >    Please watch this 4-minute video at
>      >    [1][6]http://www.youtube.com/watch?v=LbLaPpwNAx4
>      >
>      >    I have only started 3 HVM Linux guests with 1 GB ram each. I can't
>      start
>      >    the 4th HVM guest. If I attempt to start the 4th instance, it will
>      crash
>      >    dom0.
>      >
>      >    Are there anything in the xm dmesg output that could explain the
>      low limit
>      >    to the number of VMs that I could start before dom0 becomes
>      unresponsive?
>      >
> 
>      Have you limited dom0 memory (by specifying dom0_mem=XMB option in
>      grub.conf for xen.gz) ?
> 
>      What does "xm info" say about free memory before starting any guests?
>      -- Pasi
> 
> References
> 
>    Visible links
>    1. http://teo-en-ming-aka-zhang-enming.blogspot.com/
>    2. http://enmingteo.wordpress.com/
>    3. http://www.youtube.com/user/enmingteo
>    4. mailto:space.time.universe@xxxxxxxxx
>    5. mailto:pasik@xxxxxx
>    6. http://www.youtube.com/watch?v=LbLaPpwNAx4

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