>>> On 2009/11/09 at 05:05, Pasi Kärkkäinen<pasik@xxxxxx> wrote:
> 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.
Really? I thought current conventional wisdom was to allow Xen to
self-manage memory in both dom0 and domUs, and not to manually adjust
this? I run several Xen systems with anywhere from 8 to 24 GB of RAM
and 20 to 30 domUs on some of these systems and have *never* specified
the dom0 memory at boot time - the Xen ballooning has always functioned
perfectly fine, and never crashed my dom0. Furthermore, while I'm not
Linux developer and so not familiar with how Linux calculates buffering
and caching, I do know that my Linux systems dynamically manage buffers
and caches, and when memory is reduced or some application requires a
larger amount of physical memory, Linux reduces the amount of data in
buffers and caches.
Of course, a lot of this depends on what you're doing in dom0 - on my
Xen servers, my dom0 is strictly for Xen management - I'm not running
anything else in dom0 that would require large amounts of memory, memory
buffers and caches, etc.
-Nick
>
> 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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