nova/releasenotes/notes/bug-1882821-file-backed-memory-reserved-conflict-3ad4c04ab993ebf8.yaml
Stephen Finucane 3b99747b42 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@redhat.com>
Closes-Bug: #1882821
2020-06-10 10:40:59 +00:00

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YAML

---
upgrade:
- |
When using file-backed memory, the ``nova-compute`` service will now fail
to start if the amount of reserved memory configured using ``[DEFAULT]
reserved_host_memory_mb`` is equal to or greater than the total amount of
memory configured using ``[libvirt] file_backed_memory``. Where reserved
memory is less than the total amount of memory configured, a warning will
be raised. This warning will become an error in a future release.
The former combination is invalid as it would suggest reserved memory is
greater than total memory available, while the latter is considered
incorrect behavior as reserving of file-backed memory can and should be
achieved by reducing the filespace allocated as memory by modifying
``[libvirt] file_backed_memory``.