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Excellent answer thank you sir.
One doubt comes into my mind is for this reservation to work RAM over
committing should be disabled?
ie ram_allocation_ratio=1
Thanks for your help


On Thu, Nov 27, 2014 at 7:20 PM, Luis Fernandez Alvarez
<luis.fernandez.alvarez at cern.ch> wrote:
> Hi,
>
> In general, you can see 'reserved_host_memory_mb' as your estimation of how
> much memory your hypervisor needs. From the point of view of Nova, your
> system is consuming the amount you set in 'reserved_host_memory_mb' [0].
>
> Then, the field 'free_ram_mb' (the one that is checked when VMs are being
> scheduled) is calculated using the memory consumed by the instances and the
> value of reserved memory [1].
>
> Said that, the scheduler won't see the real free mem (700Mb in your case),
> it will see the calculated value. I would suggest you take a look to the
> value of "free_ram_mb" on your hypervisor (the value in the database: like
> "nova hypervisor-show", not the one in the compute logs), and then... you
> compare. If you're expection 700Mb and you see 900Mb, you should tweak a bit
> more your 1024Mb or reserved memory and increase it.
>
> It's a bit difficult to follow the flow in the code, but these links are
> quite useful to understand how it works.
>
> [0]
> https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L695
> https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L708
> [1]
> https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L532
>
>
>
> On 11/27/2014 01:55 PM, mad Engineer wrote:
>>
>> it reports "Free ram (MB): 425"
>> but free -m has different result.
>>
>> Is it working for you.Are you using icehouse
>>
>> On Thu, Nov 27, 2014 at 6:16 PM, George Mihaiescu <lmihaiescu at gmail.com>
>> wrote:
>>>
>>> Then I would enable debug and verbose in nova.conf and restart the
>>> scheduler
>>> service. In this way you should see in the logs the entire scheduler
>>> logic
>>> and what resources it thinks your host has.
>>>
>>> On 27 Nov 2014 06:20, "mad Engineer" <themadengin33r at gmail.com> wrote:
>>>>
>>>> George,
>>>>                overcommit of RAM is 1  and that is working.However
>>>> instances are still getting created with available free memory <
>>>> reserved_host_memory_mb
>>>>
>>>> On Thu, Nov 27, 2014 at 4:33 PM, George Mihaiescu <lmihaiescu at gmail.com>
>>>> wrote:
>>>>>
>>>>> Depending on your overcommit ratio, the scheduler can schedule
>>>>> instances
>>>>> using more virtual memory than the available physical memory on the
>>>>> host,
>>>>> 700 MB in your case.
>>>>>
>>>>> On 27 Nov 2014 05:36, "mad Engineer" <themadengin33r at gmail.com> wrote:
>>>>>>
>>>>>> hi all i have set
>>>>>> reserved_host_memory_mb in nova.conf of controller and compute and
>>>>>> restarted necessary services.
>>>>>> i am expecting scheduler to not pickup host that has less than what is
>>>>>> reserved_host_memory_mb
>>>>>> in my example i put reserved_host_memory_mb = 1024
>>>>>> and free RAM in compute node is 700 Mb.
>>>>>> But still scheduler chooses this host and created a new instance on
>>>>>> it.I
>>>>>> am expecting scheduler to show "No valid Hosts found" as it has less
>>>>>> ram
>>>>>> than reserved_host_memory_mb = 1024
>>>>>>
>>>>>> Can some one help me understand this value
>>>>>>
>>>>>> Thanks
>>>>>>
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>
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