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<p class="MsoPlainText">Hi all,<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">While I was working on fixing the resize for pci passthrough [1] I have notice the following issue in resize.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">If you are using small image and you resize-confirm it very fast the old resources are not getting freed.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">After debug this issue I found out the root cause of it. <o:p>
</o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">A Good run of resize is as detailed below: <o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">When doing resize the _update_usage_from_migration in the resource trucker called twice.<o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>The first call we return the instance type of the new flavor and will enter this case
<o:p></o:p></p>
<p class="MsoPlainText"> <a href="https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L718">https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L718</a><o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>Then it will put in the tracked_migrations the migration and the new instance_type
<o:p></o:p></p>
<p class="MsoPlainText"> <a href="https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763">https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763</a><o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>The second call we return the old instance_type and will enter this case<o:p></o:p></p>
<p class="MsoPlainText"> <a href="https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L725">https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L725</a><o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>Then in the tracked_migrations it will overwrite the old value with migration and the old instance type<o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">5.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span><a href="https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763">https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763</a><o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">6.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>When doing resize-confirm the drop_move_claim called with the old instance type
<o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in"><a href="https://github.com/openstack/nova/blob/9a05d38f48ef0f630c5e49e332075b273cee38b9/nova/compute/manager.py#L3369">https://github.com/openstack/nova/blob/9a05d38f48ef0f630c5e49e332075b273cee38b9/nova/compute/manager.py#L3369</a><o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">7.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>The <span class="pl-en">drop_move_claim will compare the instance_type[id] from the
</span>tracked_migrations to the instance_type.id <span class="pl-en">(which is the old one)</span><o:p></o:p></p>
<p class="MsoPlainText" style="margin-left:.75in;text-indent:-.25in;mso-list:l1 level1 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">8.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>And because they are equals it will
<span class="pl-en"> remove the old resource usage</span><o:p></o:p></p>
<p class="MsoPlainText"> <a href="https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L328">https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L328</a>
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">But with small image like CirrOS and doing the revert-confirm fast the second call of _update_usage_from_migration will not get executing.<o:p></o:p></p>
<p class="MsoPlainText">The result is that when we enter the <span class="pl-en">
drop_move_claim it compares it with the new instance_type and this expression is false
<a href="https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L314">
https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L314</a><o:p></o:p></span></p>
<p class="MsoPlainText"><span class="pl-en">This mean that this code block is not executed <a href="https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L326">https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L326</a>
and therefore </span>old resources are not getting freed.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Any thought on the matter?<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">[1] - <a href="https://review.openstack.org/#/c/307124/">
https://review.openstack.org/#/c/307124/</a> <o:p></o:p></p>
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