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[OpenStack Infra <1698383@xxxxxxxxxxxxxxxxxx>]

*** This bug is a duplicate of bug 1635367 ***
    https://bugs.launchpad.net/bugs/1635367

Reviewed:  https://review.openstack.org/474994
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=0ddf3ce01149d78ee0cf8f7497f8a9074c6f167d
Submitter: Jenkins
Branch:    master

commit 0ddf3ce01149d78ee0cf8f7497f8a9074c6f167d
Author: Dan Smith <dansmith@xxxxxxxxxx>
Date:   Fri Jun 16 07:25:40 2017 -0700

    Fix regression preventing reporting negative resources for overcommit
    
    In Nova prior to Ocata, the scheduler computes available resources for
    a compute node, attempting to mirror the same calculation that happens
    locally. It does this to determine if a new instance should fit on the
    node. If overcommit is being used, some of these numbers can be negative.
    
    In change 016b810f675b20e8ce78f4c82dc9c679c0162b7a we changed the
    compute side to never report negative resources, which was an ironic-
    specific fix for nodes that are offline. That, however, has been
    corrected for ironic nodes in 047da6498dbb3af71bcb9e6d0e2c38aa23b06615.
    Since the base change to the resource tracker has caused the scheduler
    and compute to do different math, we need to revert it to avoid the
    scheduler sending instances to nodes where it believes -NNN is the
    lower limit (with overcommit), but the node is reporting zero.
    
    This doesn't actually affect Ocata because of our use of the placement
    engine. However, this code is still in master and needs to be backported.
    This part of the change actually didn't even have a unit test, so
    this patch adds one to validate that the resource tracker will
    calculate and report negative resources.
    
    Change-Id: I25ba6f7f4e4fab6db223368427d889d6b06a77e8
    Closes-Bug: #1698383


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

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https://bugs.launchpad.net/bugs/1698383

Title:
  Resource tracker regressed reporting negative memory

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  Nova's resource tracker is expected to publish negative values to the
  scheduler when resources are overcommitted. Nova's scheduler expects
  this:

  https://github.com/openstack/nova/blob/a43dbba2b8feea063ed2d0c79780b4c3507cf89b/nova/scheduler/host_manager.py#L215

  In change https://review.openstack.org/#/c/306670, these values were
  filtered to never drop below zero, which is incorrect. That change was
  making a complex alteration for ironic and cells, specifically to
  avoid resources from ironic nodes showing up as negative when they
  were unavailable. That was a cosmetic fix (which I believe has been
  corrected for ironic only in this patch:

  https://review.openstack.org/#/c/230487/

  Regardless, since the scheduler does the same calculation to determine
  available resources on the node, if the node reports 0 when the
  scheduler calculates -100 for a given resource, the scheduler will
  assume the node till has room (due to oversubscription) and will send
  builds there destined to fail.

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