6:21 p.m.
Hello,
i just tested the memory hot add to a vm. This vm had 2048 MB. I set
the new memory to 2662 MB.
I logged into the vm and i've seen that hasn't been any memory change,
even if i said to the manager to apply memory expansion immediately.
Memory shown by free -m is 1772 MB.
Looking around i've found that that value was set in the option called
"Physical Memory guaranteed".
I tried setting this parameter to an higher value, but is still
showing 1772, even if it says that "Memory" parameter will be changed
immediately and minAllocatedMemory is changed at next boot.
What is the right workflow to hot increase the ram of a vm?
Luca
--
"E' assurdo impiegare gli uomini di intelligenza eccellente per fare
calcoli che potrebbero essere affidati a chiunque se si usassero delle
macchine"
Gottfried Wilhelm von Leibnitz, Filosofo e Matematico (1646-1716)
"Internet è la più grande biblioteca del mondo.
Ma il problema è che i libri sono tutti sparsi sul pavimento"
John Allen Paulos, Matematico (1945-vivente)
Luca 'remix_tj' Lorenzetto, http://www.remixtj.net ,
<lorenzetto.luca(a)gmail.com>
6:25 p.m.
On Thu, Jun 22, 2017 at 6:21 PM, Luca 'remix_tj' Lorenzetto
<lorenzetto.luca(a)gmail.com> wrote:
Hello,
i just tested the memory hot add to a vm. This vm had 2048 MB. I set
the new memory to 2662 MB.
I logged into the vm and i've seen that hasn't been any memory change,
even if i said to the manager to apply memory expansion immediately.
Memory shown by free -m is 1772 MB.
Looking around i've found that that value was set in the option called
"Physical Memory guaranteed".
I tried setting this parameter to an higher value, but is still
showing 1772, even if it says that "Memory" parameter will be changed
immediately and minAllocatedMemory is changed at next boot.
What is the right workflow to hot increase the ram of a vm?
forgot to say that is a RHEL 7 VM and has the memory baloon device enabled.
I tried on a RHEL 6 that has no memory baloon device and the ram has
been immediately increased.
--
"E' assurdo impiegare gli uomini di intelligenza eccellente per fare
calcoli che potrebbero essere affidati a chiunque se si usassero delle
macchine"
Gottfried Wilhelm von Leibnitz, Filosofo e Matematico (1646-1716)
"Internet è la più grande biblioteca del mondo.
Ma il problema è che i libri sono tutti sparsi sul pavimento"
John Allen Paulos, Matematico (1945-vivente)
Luca 'remix_tj' Lorenzetto, http://www.remixtj.net ,
<lorenzetto.luca(a)gmail.com>
11:16 a.m.
"Luca 'remix_tj' Lorenzetto" <lorenzetto.luca(a)gmail.com> writes:
i just tested the memory hot add to a vm. This vm had 2048 MB. I set
the new memory to 2662 MB.
I logged into the vm and i've seen that hasn't been any memory change,
even if i said to the manager to apply memory expansion immediately.
Memory shown by free -m is 1772 MB.
[...]
forgot to say that is a RHEL 7 VM and has the memory baloon device
enabled.
This is normal with memory balloon enabled – memory balloon often
"consumes" the hot plugged memory, so you can't see it.
Regards,
Milan
11:49 a.m.
And I believe the virt team is working on "hotplug" support for the
guaranteed memory so mom will start changing the balloon size
accordingly.
Michal: is there a bug tracking that?
Regards,
Martin Sivak
On Fri, Jun 23, 2017 at 11:16 AM, Milan Zamazal <mzamazal(a)redhat.com> wrote:
"Luca 'remix_tj' Lorenzetto"
<lorenzetto.luca(a)gmail.com> writes:
> i just tested the memory hot add to a vm. This vm had 2048 MB. I set
> the new memory to 2662 MB.
> I logged into the vm and i've seen that hasn't been any memory change,
> even if i said to the manager to apply memory expansion immediately.
>
> Memory shown by free -m is 1772 MB.
[...]
> forgot to say that is a RHEL 7 VM and has the memory baloon device enabled.
This is normal with memory balloon enabled – memory balloon often
"consumes" the hot plugged memory, so you can't see it.
Regards,
Milan
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11:58 a.m.
On Fri, Jun 23, 2017 at 11:16 AM, Milan Zamazal <mzamazal(a)redhat.com> wrote:
"Luca 'remix_tj' Lorenzetto"
<lorenzetto.luca(a)gmail.com> writes:
> i just tested the memory hot add to a vm. This vm had 2048 MB. I set
> the new memory to 2662 MB.
> I logged into the vm and i've seen that hasn't been any memory change,
> even if i said to the manager to apply memory expansion immediately.
>
> Memory shown by free -m is 1772 MB.
[...]
> forgot to say that is a RHEL 7 VM and has the memory baloon device enabled.
This is normal with memory balloon enabled – memory balloon often
"consumes" the hot plugged memory, so you can't see it.
Ok.
What's exactly the role of "guaranteed memory"? Is only about ensuring
on startup time that there is at least X free memory on hosts or
something more complex?
What's the best configuration? keeping baloon or not? setting memory
and guaranteed memory to the same value?
If i have 1TB of ram in all the cluster, does the "guaranteed memory"
doesn't allows to provision vms with cumulative guaranteed memory
usage greater than 1TB?
Can KSM help allow to overprovision in this situation?
Does memory baloon device has impacts on vm performance?
I need to understand better in order to plan correctly all the
required hardware resource i need for migrating to oVirt.
Luca
--
"E' assurdo impiegare gli uomini di intelligenza eccellente per fare
calcoli che potrebbero essere affidati a chiunque se si usassero delle
macchine"
Gottfried Wilhelm von Leibnitz, Filosofo e Matematico (1646-1716)
"Internet è la più grande biblioteca del mondo.
Ma il problema è che i libri sono tutti sparsi sul pavimento"
John Allen Paulos, Matematico (1945-vivente)
Luca 'remix_tj' Lorenzetto, http://www.remixtj.net ,
<lorenzetto.luca(a)gmail.com>
3:44 p.m.
"Luca 'remix_tj' Lorenzetto" <lorenzetto.luca(a)gmail.com> writes:
On Fri, Jun 23, 2017 at 11:16 AM, Milan Zamazal
<mzamazal(a)redhat.com> wrote:
> "Luca 'remix_tj' Lorenzetto" <lorenzetto.luca(a)gmail.com>
writes:
>
>> i just tested the memory hot add to a vm. This vm had 2048 MB. I set
>> the new memory to 2662 MB.
>> I logged into the vm and i've seen that hasn't been any memory change,
>> even if i said to the manager to apply memory expansion immediately.
>>
>> Memory shown by free -m is 1772 MB.
>
> [...]
>
>> forgot to say that is a RHEL 7 VM and has the memory baloon device enabled.
>
> This is normal with memory balloon enabled – memory balloon often
> "consumes" the hot plugged memory, so you can't see it.
Ok.
What's exactly the role of "guaranteed memory"? Is only about ensuring
on startup time that there is at least X free memory on hosts or
something more complex?
I think it defines the minimum memory that the balloon should always
leave available.
Martin, do you know answers to the other questions?
What's the best configuration? keeping baloon or not? setting
memory
and guaranteed memory to the same value?
If i have 1TB of ram in all the cluster, does the "guaranteed memory"
doesn't allows to provision vms with cumulative guaranteed memory
usage greater than 1TB?
Can KSM help allow to overprovision in this situation?
Does memory baloon device has impacts on vm performance?
I need to understand better in order to plan correctly all the
required hardware resource i need for migrating to oVirt.
Luca
4:14 p.m.
What's exactly the role of "guaranteed memory"? Is only
about ensuring
on startup time that there is at least X free memory on hosts or
something more complex?
As Milan said, it tells the balloon the lower limit of ballooning. We
won't take more memory from the VM when it reaches this amount of
assigned memory. It is not related to VM start, but to runtime.
It is important to realize that both overcommit features (KSM,
ballooning) require that the full VM can be started first. Only then
will KSM start deduplicating pages and balloon inflating.
That is why we recommend swap to be present and enabled on a host
although it won't be really used, it just provides a buffer space
before the VM is compacted.
What's the best configuration? keeping baloon or not? setting
memory
and guaranteed memory to the same value?
Setting the two fields to the same value effectively disables
ballooning for the VM.
If i have 1TB of ram in all the cluster, does the "guaranteed
memory"
doesn't allows to provision vms with cumulative guaranteed memory
usage greater than 1TB?
No, the memory field itself behaves like this. You can allow the
consumption go higher by defining memory overcommit ratio (in Edit
Cluster dialog). Guaranteed memory is only used for controlling
balloon limits.
Can KSM help allow to overprovision in this situation?
KSM is complementary to ballooning in this case. Both features allow
over commit to work.
- KSM needs no cooperation of the VM, but scanning for duplicate pages
loads the host
- ballooning needs cooperation of the VM (driver + guest agent)
Does memory baloon device has impacts on vm performance?
Well the device itself does not impose any load. But when you take
some memory from the VM, it will have obviously less resources. If the
VM tends to allocate huge amount of memory in short time then the
balloon might be slow in returning the memory to the VM and the
application might not be happy about it.
Best regards
Martin Sivak
On Fri, Jun 23, 2017 at 11:58 AM, Luca 'remix_tj' Lorenzetto
<lorenzetto.luca(a)gmail.com> wrote:
> On Fri, Jun 23, 2017 at 11:16 AM, Milan Zamazal <mzamazal(a)redhat.com> wrote:
>> "Luca 'remix_tj' Lorenzetto" <lorenzetto.luca(a)gmail.com>
writes:
>>
>>> i just tested the memory hot add to a vm. This vm had 2048 MB. I set
>>> the new memory to 2662 MB.
>>> I logged into the vm and i've seen that hasn't been any memory
change,
>>> even if i said to the manager to apply memory expansion immediately.
>>>
>>> Memory shown by free -m is 1772 MB.
>>
>> [...]
>>
>>> forgot to say that is a RHEL 7 VM and has the memory baloon device enabled.
>>
>> This is normal with memory balloon enabled – memory balloon often
>> "consumes" the hot plugged memory, so you can't see it.
>
> Ok.
>
What's exactly the role of "guaranteed memory"? Is only
about ensuring
on startup time that there is at least X free memory on hosts or
something more complex?
>
What's the best configuration? keeping baloon or not? setting
memory
and guaranteed memory to the same value?
If i have 1TB
of ram in all the cluster, does the "guaranteed memory"
doesn't allows to provision vms with cumulative guaranteed memory
usage greater than 1TB?
Can KSM help allow to overprovision in
this situation?
>
Does memory baloon device has impacts on vm performance?
>
> I need to understand better in order to plan correctly all the
> required hardware resource i need for migrating to oVirt.
>
> Luca
>
> --
> "E' assurdo impiegare gli uomini di intelligenza eccellente per fare
> calcoli che potrebbero essere affidati a chiunque se si usassero delle
> macchine"
> Gottfried Wilhelm von Leibnitz, Filosofo e Matematico (1646-1716)
>
> "Internet è la più grande biblioteca del mondo.
> Ma il problema è che i libri sono tutti sparsi sul pavimento"
> John Allen Paulos, Matematico (1945-vivente)
>
> Luca 'remix_tj' Lorenzetto, http://www.remixtj.net ,
<lorenzetto.luca(a)gmail.com>
> _______________________________________________
> Users mailing list
> Users(a)ovirt.org
> http://lists.ovirt.org/mailman/listinfo/users
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6 comments
3 participants
participants (3)
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Luca 'remix_tj' Lorenzetto -
Martin Sivak -
Milan Zamazal