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[melanie witt <1402502@xxxxxxxxxxxxxxxxxx>]

Hi Jin,

I researched into this based on your comment and found some interesting
things. From a technical, virt-level standpoint, you are right that
resources on the hypervisor can be freed after suspending an instance. I
think it's hypervisor dependent, but in the case of libvirt, I did
observe that the hypervisor nova-compute.log showed vcpus decrease by 1
when I suspended a tiny instance.

However, I still could not schedule an extra instance on the hypervisor
with cpu_allocation_ratio = 1.0 like you said. I found this is because
the nova scheduler (which uses the resource tracker) computes resource
usage based on data like, how many instances are on the hypervisor, what
size are they, etc and does *not* use the values reported by the
hypervisor. There are likely many reasons for this, some of which I
think are if you scheduled the extra instance while one was suspended,
and you resume the suspended one, you can immediately get into an
overcommit situation you didn't intend, unless you migrate the extra
instance, etc. Another reason might be race conditions between what the
nova db knows and what the hypervisor sees.

So, it appears the bug here is in the user documentation, unfortunately.
I will update this bug report as a Wishlist item for desired change in
behavior, and add the documentation project so that can be fixed.

** Changed in: nova
   Importance: Undecided => Wishlist

** Changed in: nova
       Status: Incomplete => Opinion

** Tags added: scheduler

** Also affects: openstack-manuals
   Importance: Undecided
       Status: New

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Engineering Team, which is subscribed to OpenStack Compute (nova).
https://bugs.launchpad.net/bugs/1402502

Title:
  Resource usage will not be updated when suspending instance

Status in OpenStack Compute (Nova):
  Opinion
Status in OpenStack Manuals:
  New

Bug description:
  Suspending instance will not update resource usage.

  Instance suspending should move all contents in the ram to hard disk.
  Then vcpu and used memory should be decreased and hard disk useage should be increased.
  However it didn't happen.

  This will lead to trouble in the following scenario:
  When the memory of all compute nodes are exhaust, to create a new instance, it's useless to suspend some alive instances, but have to delete them.

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