[Question] how to avoid Xen using a memory range?

[Question] how to avoid Xen using a memory range?

[Chao Gao]

Hi, everyone.

I have a machine which has two numa nodes. The NODE0 contains
memory range from 0 to 0x18400MB and NODE1 contains memory range
from 0x18400MB to 0x1c400MB. The resource available to dom0 is
restricted through adding "dom0_mem=10G dom0_nodes=0 dom0_max_vcpus=48"
to Xen Command Line. Even though no guest is created, over 1GB memory of
NODE1 is consumed according the output of 'xl info -n'. From 'xl
debug-keys u', I found dom0 used a lot of pages of NODE1. And after
adding "highmem-start=0x18400MB" to Xen Command Line to avoid relocating
dom0's image to NODE1, near 1GB memory of NODE1 is still in
use. Considering no cpu on NODE1, I think Xen won't allocate memory from
NODE1 if no numa node is specified. Do you have some ideas about what is 
using the memory of NODE1? and how to avoid this?

Thanks
Chao

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Re: [Question] how to avoid Xen using a memory range?

[Jan Beulich]

>>> Chao Gao <chao.gao@intel.com> 08/04/17 10:12 AM >>>
>I have a machine which has two numa nodes. The NODE0 contains
>memory range from 0 to 0x18400MB and NODE1 contains memory range
>from 0x18400MB to 0x1c400MB. The resource available to dom0 is
>restricted through adding "dom0_mem=10G dom0_nodes=0 dom0_max_vcpus=48"
>to Xen Command Line. Even though no guest is created, over 1GB memory of
>NODE1 is consumed according the output of 'xl info -n'. From 'xl
>debug-keys u', I found dom0 used a lot of pages of NODE1. And after
>adding "highmem-start=0x18400MB" to Xen Command Line to avoid relocating
>dom0's image to NODE1, near 1GB memory of NODE1 is still in
>use. Considering no cpu on NODE1, I think Xen won't allocate memory from
>NODE1 if no numa node is specified. Do you have some ideas about what is 
>using the memory of NODE1? and how to avoid this?

How to avoid it depends on understanding what it's being used for: You'll
have to do some debugging yourself to find out, I'm afraid. I, at least, have
no immediate idea.

Jan


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