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Re: [Xen-users] [Xen-API] Problem with parameter "GRUB_CMDLINE_XEN"!

  • To: XenUsers <xen-users@xxxxxxxxxxxxx>
  • From: Alexandre Kouznetsov <alk@xxxxxxxxxx>
  • Date: Tue, 05 Mar 2013 15:56:00 -0600
  • Delivery-date: Tue, 05 Mar 2013 21:57:14 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>


El 05/03/13 12:32, Eduardo LÃcio A. Costa escribiÃ:
I have configured the file "/etc/default/grub" on "Dom0" with the
following parameter...

GRUB_CMDLINE_XEN="dom0_mem=16G,max:16G dom0_max_vcpus=8"
  - Kouznetsov -> Assuming your machine has this amount of memory, I may 
suggest this
troubleshooting actions...
  - LÃcio -> Yes, the server has 128 GB! =]
Ok. Is all that memory visible to the hypervisor? xentop shall show it.

  - Kouznetsov -> After this command, check /boot/grub/grub.conf (or menu.list, 
if Grub v1
is used). Make sure Xen's entry has the desired parameter. Otherwise,
it's your update-grub script fault.
  - LÃcio -> The command "update-grub" runs correctly. No error is returned!
The point was to look at the result, not at the error output, inspecting the resulting Grub configuration file. Well, your next answer discards Grub as the cause.

reboot -h 0
  - Kouznetsov -> While rebooting, inspect Xen's command line in the boot 
loader (press
'E' over Grub's menu entry). Make sure the desired parameter is there.
Otherwise, your boot loader is using a wrong config file (or you have
updated a wrong one).
  - LÃcio -> The "boot loader" contains this line "multiboot /xen-4.1-amd64.gz 
placeholder dom0_mem=16G,max:16G dom0_max_vcpus=8" among other things.
That seems fine, we can discard boot loader as the cause of the issue.

The reference [1] is not clear about if "max:" and "min:" are optional both or each, i.e. it they have to be used both or none, or may be used individually. Why don't you try to set a fixed amount of RAM to Dom0, as "dom0_mem=16G", without a "max:"? Even if that is not exactly what you intend, at least it would tell us if there is a problem grabbing the whole dom0_mem variable, or parsing it's value.

Also, inspect carefully your Xen's dmesg (xm dmesg), maybe it mentions something about RAM assignment to Dom0.

But when the "Dom0" returns, I have only just "3465592" of total memory.
  - Kouznetsov -> Once booted, check with xentop or "xm list" or "xl list" 
(depends on
what toolstack you are using). Inspect, how much memory did Xen assigned
to Domain-0 aka Dom0.
  - LÃcio -> "xentop" shows this:
       NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)  MAXMEM(k) MAXMEM(%) 
   Domain-0 -----r       1131  114.0    3877888    2.9    3877888       2.9     
Thais suggests that it's entirely hypervisor's issue. Dom0 is assigned with low RAM.

  - Kouznetsov -> Note, that if your Dom0 is a 32 bits system, it won't be able 
to see
more RAM unless some workaround is activated, like using x86_64 kernel
or activating PAE.
  - LÃcio -> This is my Dom0: "Ubuntu 12.04.1 LTS (GNU/Linux 3.2.0-29-generic 

[1] http://wiki.xen.org/xenwiki/XenHypervisorBootOptions

Alexandre Kouznetsov

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