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Re: [Xen-users] Unstable/inconsistent auto-start of domUs under Xen-4.8/Linux-4.9

  • To: xen-users@xxxxxxxxxxxxx
  • From: Daniel Widenfalk <Daniel@xxxxxxxxxxxx>
  • Date: Fri, 10 Mar 2017 14:38:14 +0100
  • Delivery-date: Fri, 10 Mar 2017 13:38:56 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

On 2017-03-10 13:40, Simon Hobson wrote:
Daniel Widenfalk <Daniel@xxxxxxxxxxxx> wrote:

2) Disable balooning on Dom0. My Dom0 will never run anything memory
  intensive so limiting it to, say, 4GB would not be a severe

Common advice is to hard-wire Dom0 to a fixed memory allocation via a dom0_mem 
statement in your grub config. I have this in mine :
multiboot /xen-4.1-amd64.gz placeholderdom0_mem=512M dom0_max_vcpus=1 

which in Debian comes from an entry in /etc/default/grub of
GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=512M dom0_max_vcpus=1 dom0_vcpus_pin=true"

One thought is that you've a race condition where you've multiple VMs all 
causing massive ballooning in Dom0 - and Xen is timing out because it can't get 
the memory fast enough. I;d have thought something would show in the logs for 
that though.
Apart from this, setting Dom0 memory is more efficient as various kernel 
structures are sized at boot time based on memory size. So having Dom0 working 
with a fixed smaller memory will reduce the size of these structures. Don't 
know how much memory this actually releases ...

Many thanks for the quick reply. I disabled balooning on dom0 and now
all the domUs start up cleanly on re-boot.

/Daniel W

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