Comment 4 for bug 1882821

Reviewed: https://review.opendev.org/736219
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=9d3ebd58aa6a7514ab4db401980848570415706a
Submitter: Zuul
Branch: stable/ussuri

commit 9d3ebd58aa6a7514ab4db401980848570415706a
Author: Stephen Finucane <email address hidden>
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 <email address hidden>
    Closes-Bug: #1882821
    (cherry picked from commit 3b99747b42e460567d52cc6d748396cb349d56b8)