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Re: [Xen-users] GRUB boot parameters: dom0_mem


  • To: "xen-users@xxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxx>
  • From: Eric <epretorious@xxxxxxxxx>
  • Date: Wed, 20 Jun 2012 23:01:25 -0700 (PDT)
  • Cc: "Fajar A. Nugraha" <list@xxxxxxxxx>
  • Delivery-date: Thu, 21 Jun 2012 06:02:18 +0000
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  • List-id: Xen user discussion <xen-users.lists.xen.org>

Thanks, Everybody:

This question has already been addressed on this list and Faraj gave a very complete answer that differs slightly...

It's not mandatory to have that parameter, but it's considered best
practice. When ommitted, dom0 will use all available memory and
ballon-down as needed when domUs are started. Depending on what you
have running on dom0, ballooning down MIGHT cause a problem.

So if you know (for example) that you have 4G memory, 512M will be
allocated to dom0 while the reset will be used for domUs, you should
set something like

kernel /xen.gz-3.3.1 dom0_mem=512M

on grub.conf, and have this entry on /etc/xen/xend-config.sxp

(dom0-min-mem 512)

These will effectively prevents dom0 from ballooning down memory.

I verified that relocating the dom0_mem parameter to the top line (i.e., kernel /xen.gz...) fixed the problem.

I apologize for duplicating the topic and, in the future, will search the archives first.  ;)

Eric Pretorious
Truckee, CA


From: Eric <epretorious@xxxxxxxxx>
To: Randy Katz <rkatz@xxxxxxxxxxxxxxxxxxxxx>
Cc: "xen-users@xxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxx>
Sent: Wednesday, June 20, 2012 10:48 PM
Subject: Re: [Xen-users] GRUB boot parameters: dom0_mem

Thanks, Randy:

I tried that boot parameter in both my nested environment and on my baremetal hypervisor (below) and did not see any change.

[eric@xen2 ~]$ sudo cat /boot/grub/menu.lst
...
title CentOS (2.6.18-274.el5xen)
    root (hd0,0)
    kernel /xen.gz-2.6.18-274.el5
    module /vmlinuz-2.6.18-274.el5xen ro root=LABEL=/ dom0_mem=512M
    module /initrd-2.6.18-274.el5xen.img

[eric@xen2 ~]$ cat /proc/cmdline
ro root=LABEL=/ dom0_mem=512M

Might I have overlooked something?

Eric Pretorious
Truckee, CA


From: Randy Katz <rkatz@xxxxxxxxxxxxxxxxxxxxx>
To: Eric <epretorious@xxxxxxxxx>
Cc: xen-users@xxxxxxxxxxxxx
Sent: Wednesday, June 20, 2012 9:41 PM
Subject: Re: [Xen-users] GRUB boot parameters: dom0_mem

Hi,

from my grub.conf file:

module /vmlinuz-2.6.18-274.7.1.el5xen ro root=LABEL=/ nodmraid dom0_mem=512M pci=nomsi

I have heard talk of 256M but have not tried it yet.

Regards,
Randy


--- Original message ---
Subject: [Xen-users] GRUB boot parameters: dom0_mem
From: Eric <epretorious@xxxxxxxxx>
To: xen-users@xxxxxxxxxxxxx <xen-users@xxxxxxxxxxxxx>
Date: Thursday, 21/06/2012 11:35 AM

I've installed Xen Hypervisor 3.0.3 (CentOS 5.7, i386) inside Virtualbox 4.1.16 (Mageia 1, i686) and have noticed that Dom0 is consuming 85% of the memory allocated to the VM (1GB) so I'd like to reduce this as much as possible in order to make more room for one or two VM's.

Is there a minimum amount of vRAM that can/should be allocated to Dom0 (using the dom0_mem boot parameter) considering that I only want to host one or two VM's?

Eric Pretorious
Truckee, CA
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