Does 'numad' interacts with memory_migration with 'numatune'?
Daniel Henrique Barboza
danielhb413 at gmail.com
Thu Jun 11 16:01:41 UTC 2020
While investigating a 'virsh numatune' behavior in Power 9 guests I came
across this doubt and couldn't find a direct answer.
numad role, as far as  goes, is automatic NUMA affinity only. As far as
Libvirt and my understanding goes , numad is used for placement='auto' setups,
which aren't even allowed for numatune operations in the first place.
Problem is that I'm not sure if the mere presence of numad running in the
host might be accelerating the memory migration triggered by numatune,
regardless of placement settings. My first answer would be no, but several
examples in the internet shows all the RAM in the guest being migrated
from one NUMA node to the other almost instantly*, and aside from them being
done in x86 I wonder whether numad is having any impact on that.
The reason I'm asking is because I don't have a x86 setup with multiple
NUMA nodes to compare results, and numad is broken sparse NUMA setups for some
time now ( tells the story if you're interested), and Power 8/9 happens
to operate with sparse NUMA setups, so no numad for me.
If someone can confirm my suspicion (i.e. numad has no interference in NUMA
memory migration triggered by numatune) I appreciate.
* or at very least no one cared to point out that the memory is migrated
according to the paging demanding of the guest, as I see happen in Power
guests and working as intended according to kernel cgroup docs.
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