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[OpenStack Infra <1882821@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/734658
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=3b99747b42e460567d52cc6d748396cb349d56b8
Submitter: Zuul
Branch:    master

commit 3b99747b42e460567d52cc6d748396cb349d56b8
Author: Stephen Finucane <stephenfin@xxxxxxxxxx>
Date:   Tue Jun 9 18:38:10 2020 +0100

    libvirt: Don't allow "reserving" file-backed memory
    
    When file-backed memory is configured, it is the only "memory" reported
    by nova and used by instances, with RAM used in caching capacity. We
    should be warning users of this and insisting they explicitly configure
    the '[DEFAULT] reserved_host_memory_mb' config option to 0. However,
    doing so now would be breaking change. Instead, start logging a warning
    instead, failing only for the truly broken combination of reserving more
    file-backed memory than we have allocated.
    
    Change-Id: I9619338ad0f60253b628d96543f8ce3ac86242e3
    Signed-off-by: Stephen Finucane <stephenfin@xxxxxxxxxx>
    Closes-Bug: #1882821


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1882821

Title:
  '[libvirt] file_backed_memory' and '[DEFAULT] reserved_host_memory_mb'
  are incompatible

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  Per title, the '[libvirt] file_backed_memory' and '[DEFAULT]
  reserved_host_memory_mb' config options are incompatible. Not only
  does '[DEFAULT] reserved_host_memory_mb' not really make sense for
  file backed memory (if you want to reserve "memory", configure a lower
  '[libvirt] file_backed_memory' value) but configuring a value for
  '[libvirt] file_backed_memory' that is lower than the value for
  '[DEFAULT] reserved_host_memory_mb', which currently defaults to
  512MB, will break nova's resource reporting to placement:

    nova.exception.ResourceProviderUpdateFailed: Failed to update
  resource provider via URL
  /resource_providers/f39bde61-6f73-4ccb-9488-6efb9689730f/inventories:
  {"errors": [{"status": 400, "title": "Bad Request", "detail": "The
  server could not comply with the request since it is either malformed
  or otherwise incorrect.\n\n Unable to update inventory for resource
  provider f39bde61-6f73-4ccb-9488-6efb9689730f: Invalid inventory for
  'MEMORY_MB' on resource provider
  'f39bde61-6f73-4ccb-9488-6efb9689730f'. The reserved value is greater
  than total.  ", "code": "placement.undefined_code", "request_id":
  "req-977e43e7-1a7c-4309-96ec-49a75bdea58a"}]}

  Ideally we should error out if both values are configured, however,
  doing so would be a breaking change. Instead, we can warn if these are
  incompatible and then error our in a future release.

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