Merge "Enabled qemu memory balloon stats"
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=====================================================
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Enabled qemu memory balloon stats when boot instance
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=====================================================
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https://blueprints.launchpad.net/nova/+spec/enabled-qemu-memballoon-stats
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We can get vm memory stats from libvirt API 'virDomainMemoryStats', it help
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telemetry module like as: Ceilometer to collect vm memory usage, but by
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default the memory statistical feature is disable in qemu, we need to add
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stats period in order to enabled memory statistical.
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Problem description
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===================
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By default, the memory statistical feature is disable in qemu, we need to
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add stats period in order to enabled memory statistical, like this::
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<memballoon model='virtio'>
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<stats period='10'/>
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</memballoon>
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Add memballoon device stat period in libvirt.xml when boot instance.
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Actual memory statistical works on libvirt 1.1.1+ and qemu 1.5+, and need a
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guest driver that supports the feature, but booting instance with memory stats
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period does not lead to be failure on libvirt 0.9.6+ and qemu 1.0+.
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Refer to [1] for libvirt API 'virDomainMemoryStats' details.
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Refer to [2] for memballoon details in libvirt.xml.
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Details of enabled memory stats: [3]
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Proposed change
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===============
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* Add the option 'mem_stats_period_seconds' into nova.conf(libvirt section).
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* Enable stats period of memballoon device, if user boot instance when
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mem_stats_period_seconds > 0. mem_stats_period_seconds is number of seconds
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to memory usage statistics period. By default mem_stats_period_seconds=10.
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Alternatives
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------------
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None
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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User need to prepare suitable balloon driver in image, particularly for windows
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guests, most modern Linuxes have it built in. Booting instance will be
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successful without image balloon driver, just can't get guest memory stat from
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'virDomainMemoryStats' API.
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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Add a new option 'mem_stats_period_seconds' in nova.conf libvirt section.
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By default mem_stats_period_seconds=10, the stats feature is enable,
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mem_stats_period_seconds is number of seconds to memory usage statistics
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period. If mem_stats_period_seconds <= 0, the feature is disable.
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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<kiwik-chenrui>
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Work Items
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----------
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* Add a LibvirtConfigMemoryBalloon class inherit from LibvirtConfigGuestDevice.
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* Changes to be made to the libvirt driver get_guest_config method to check
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the option 'mem_stats_period_seconds' in nova.conf, during the boot of the
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instance.
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* If mem_stats_period_seconds>0, set stats period of memory balloon device in
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the instance.
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Dependencies
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============
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* libvirt 1.1.1+
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* qemu 1.5+
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* guest driver that supports memory balloon stats
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Testing
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=======
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Unit tests and tempest tests will verify this function. Compatibility will be
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verified, boot instance with 'mem_stats_period_seconds' on current devstack
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environment(libvirt0.9.8 and qemu1.0.0).
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Memory stats don't work in current gate environment, see details in
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Dependencies section. Full test need to ensure the devstack VM gate has updated
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libvirt, qemu versions and guest driver compatibility.
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Documentation Impact
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====================
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1. By default this feature is enabled, 'mem_stats_period_seconds'=10. If you
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want to change the stat period, please modify nova.conf.
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2. mem_stats_period_seconds is number of seconds to memory usage statistics
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period.
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3. If you set mem_stats_period_seconds<=0, the memory stats will be disabled,
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by default mem_stats_period_seconds=10.
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This blueprint just add stats period into memory balloon device, it is not
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sufficient to guarantee this feature will work because you need to meet the
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requirements in dependencies section, and you need to handle the case where
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the API 'virDomainMemoryStats' call returns no data(not in scope of this bp).
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References
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==========
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* [1] http://libvirt.org/html/libvirt-libvirt.html#virDomainMemoryStats
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* [2] http://libvirt.org/formatdomain.html#elementsMemBalloon
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* [3] http://paste.openstack.org/show/78624/
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