_assert_compute_node_has_enough_memory doesn't support ram overcommit

[Joe Breu]

Cluster configuration

compute-nodeA (4GB) of RAM reported in OS as 4010MB
1 instance launched using 2048MB RAM

compute-nodeB (4GB) of RAM reported in OS as 4010MB
2 instances launched using 2048MB RAM each

With this configuration it is not possible to migrate an instance from compute-nodeB to compute-nodeA and the scheduler reports the following:

2012-10-18 17:34:51 WARNING nova.scheduler.manager [req-ce210164-9c16-4b3a-81ab-56dfd3c52803 f8f84ef1468540fc9dfa85fcf16c53a4 29715cb8427146aeb36841b4cbc8f728] Failed to schedule_live_migratio
n: Migration error: Unable to migrate 15ca5cf7-649a-4f78-a554-9b83907eafc2 to rhel-compute1: Lack of memory(host:1962 <= instance:2048)
2012-10-18 17:34:51 ERROR nova.rpc.amqp [req-ce210164-9c16-4b3a-81ab-56dfd3c52803 f8f84ef1468540fc9dfa85fcf16c53a4 29715cb8427146aeb36841b4cbc8f728] Exception during message handling
2012-10-18 17:34:51 TRACE nova.rpc.amqp Traceback (most recent call last):
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/rpc/amqp.py", line 253, in _process_data
2012-10-18 17:34:51 TRACE nova.rpc.amqp rval = node_func(context=ctxt, **node_args)
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/scheduler/manager.py", line 97, in _schedule
2012-10-18 17:34:51 TRACE nova.rpc.amqp context, ex, *args, **kwargs)
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib64/python2.6/contextlib.py", line 23, in __exit__
2012-10-18 17:34:51 TRACE nova.rpc.amqp self.gen.next()
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/scheduler/manager.py", line 92, in _schedule
2012-10-18 17:34:51 TRACE nova.rpc.amqp return driver_method(*args, **kwargs)
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/scheduler/driver.py", line 218, in schedule_live_migration
2012-10-18 17:34:51 TRACE nova.rpc.amqp disk_over_commit)
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/scheduler/driver.py", line 301, in _live_migration_dest_check
2012-10-18 17:34:51 TRACE nova.rpc.amqp disk_over_commit)
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/scheduler/driver.py", line 389, in assert_compute_node_has_enough_resources
2012-10-18 17:34:51 TRACE nova.rpc.amqp instance_ref, dest)
2012-10-18 17:34:51 TRACE nova.rpc.amqp File "/usr/lib/python2.6/site-packages/nova/scheduler/driver.py", line 422, in assert_compute_node_has_enough_memory
2012-10-18 17:34:51 TRACE nova.rpc.amqp raise exception.MigrationError(reason=reason % locals())
2012-10-18 17:34:51 TRACE nova.rpc.amqp MigrationError: Migration error: Unable to migrate 15ca5cf7-649a-4f78-a554-9b83907eafc2 to rhel-compute1: Lack of memory(host:1962 <= instance:2048)
2012-10-18 17:34:51 TRACE nova.rpc.amqp

/etc/nova/nova.conf:
compute_scheduler_driver=nova.scheduler.filter_scheduler.FilterScheduler
scheduler_available_filters=nova.scheduler.filters.standard_filters
scheduler_default_filters=AvailabilityZoneFilter,RamFilter,ComputeFilter,CoreFilter,SameHostFilter,DifferentHostFilter
ram_allocation_ratio=1.5

[Russell Bryant (russellb)]

What nova version?

[Hans Lindgren (hanlind)]

This bug exists in trunk as well as stable/folsom.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/19369

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/19369
Committed: http://github.com/openstack/nova/commit/3783cf3cc9c571beb9c75e5b0e39bf449520aaf3
Submitter: Jenkins
Branch: master

commit 3783cf3cc9c571beb9c75e5b0e39bf449520aaf3
Author: Hans Lindgren <email address hidden>
Date: Wed Jan 9 16:01:52 2013 +0100

    Add support for memory overcommit in live-migration

    Override the live-migration memory check in FilterScheduler and
    make it use RamFilter for checking available memory on target
    host.

    Resolves bug 1068258.

    Change-Id: I3002b8330e595ce71e2718b2091d3b0b99747707

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/folsom
Review: https://review.openstack.org/22871