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Re: Actual dom0 memory much lower than dom0_mem setting
- To: Andy Smith <andy@xxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxx
- From: Jürgen Groß <jgross@xxxxxxxx>
- Date: Wed, 8 Apr 2026 15:26:05 +0200
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- Delivery-date: Wed, 08 Apr 2026 13:42:43 +0000
- List-id: Xen user discussion <xen-users.lists.xenproject.org>
On 03.04.26 17:23, Andy Smith wrote:
Hi,
Something I noticed when looking into my previous issue: Despite
dom0_memory being set to 8192M on the hypervisor command line, and
ballooning being disabled, with Xen 4.20.2 dom0 comes up with only 6353M
available to it (according to "free -m").
So, aiming to get a usable 8192M dom0 memory, I bumped it up by the
shortfall of 1839M:
$ sudo xl info | grep xen_commandline
xen_commandline : placeholder dom0_mem=10031M dom0_max_vcpus=2
com1=115200,8n1,0x2f8,10 console=com1,vga ucode=scan smt=1 no-real-mode edd=off
In case you don't need to balloon dom0 up, you can use "dom0_mem=8192,max:8192"
The problem you are seeing is that your machine has more than 100GB of memory
and the kernel is seeing this as the max. memory size it can balloon up to. So
it will reserve "some" admin memory for up to ~100GB of RAM, eating up a lot
of your usable space.
Limiting the max. memory size will reduce this overhead. You can choose larger
"max:" values in case you want to have some space available.
Juergen
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