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[Matthew Booth <mbooth@xxxxxxxxxx>]

Public bug reported:

Change I8a705114d47384fcd00955d4a4f204072fed57c2 (written by me... sigh)
addressed a bug which prevented live migration to a target host with
overcommitted disk when made with microversion <2.25. It achieved this,
but the fix is still not correct. We now do:

        if disk_over_commit:
            disk_available_gb = dst_compute_info['local_gb']

Unfortunately local_gb is *total* disk, not available disk. We actually
want free_disk_gb. Fun fact: due to the way we calculate this for
filesystems, without taking into account reserved space, this can also
be negative.

The test we're currently running is: could we fit this guest's allocated
disks on the target if the target disk was empty. This is at least
better than it was before, as we don't spuriously fail early. In fact,
we're effectively disabling a test which is disabled for microversion
>=2.25 anyway. IOW we should fix it, but it's probably not a high
priority.

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1744079

Title:
  disk over-commit still not correctly calculated during live migration

Status in OpenStack Compute (nova):
  New

Bug description:
  Change I8a705114d47384fcd00955d4a4f204072fed57c2 (written by me...
  sigh) addressed a bug which prevented live migration to a target host
  with overcommitted disk when made with microversion <2.25. It achieved
  this, but the fix is still not correct. We now do:

          if disk_over_commit:
              disk_available_gb = dst_compute_info['local_gb']

  Unfortunately local_gb is *total* disk, not available disk. We
  actually want free_disk_gb. Fun fact: due to the way we calculate this
  for filesystems, without taking into account reserved space, this can
  also be negative.

  The test we're currently running is: could we fit this guest's
  allocated disks on the target if the target disk was empty. This is at
  least better than it was before, as we don't spuriously fail early. In
  fact, we're effectively disabling a test which is disabled for
  microversion >=2.25 anyway. IOW we should fix it, but it's probably
  not a high priority.

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