[PVE-User] Hotplug Memory boots VM with 1GB

Brian Hart brianhart at ou.edu
Fri Apr 10 18:28:15 CEST 2015

Hello All,

I had some more time to play with memory hotplugging and was trying to make
this work again.  I noticed in the wiki it says it requires a kernel
greater than 3.10.  I was trying to get this to work with CentOS 6 systems
as that is primarily what we are running and it is not on a 3.x kernel
yet.  However, Cent 6 does support hotplugging memory and CPU.  I think the
issue though is the memory is hotplugged at an an odd time that the VM
isn't ready for it with CentOS 6.  Once the system boots I still see 987MB
of starting memory and if I increase the amount of memory through the
proxmox GUI the VM immediately detects all of the memory it was supposed to
have plus the additional memory I just added.  I have also found that I can
manually tell it to probe for memory by doing an "echo 0x100000000 >
/sys/devices/system/memory/probe" and it will find one piece (you have to
do this repeatedly for every module if it doesn't auto-detect the hotplug).

Anybody have an idea of how to tell CentOS 6 to detect the hotplugged
memory after boot?  Also, I'm curious why the additional memory has to be
hotplugged?  When using VMware it doesn't do it in this way so how come
KVM/QEMU does?



On Sun, Mar 8, 2015 at 8:16 PM, Brian Hart <brianhart at ou.edu> wrote:

> Ah, you're absolutely right.  It is in the wiki.  I had skipped to the
> bottom part of the wiki that said "Memory Hotplug' and overlooked the part
> that referenced Linux guests specifically.  It looks like it is probably
> udev rules I'm missing.  I will look at adding that in and try again.
> Thank you for the follow up!
> Brian
> On Sun, Mar 8, 2015 at 12:16 PM, Alexandre DERUMIER <aderumier at odiso.com>
> wrote:
>> I have updated the wiki last month about memory && cpu hotplug
>> https://pve.proxmox.com/wiki/Hotplug_%28qemu_disk,nic,cpu,memory%29
>> ----- Mail original -----
>> De: "Brian Hart" <brianhart at ou.edu>
>> À: "proxmoxve" <pve-user at pve.proxmox.com>
>> Envoyé: Samedi 7 Mars 2015 06:36:32
>> Objet: [PVE-User] Hotplug Memory boots VM with 1GB
>> Hello -
>> I'm not sure if I'm running into a bug or if I'm missing something. I
>> have done several tests playing with different settings for a VM and have
>> found that consistently whenever I set Hotplug to allow memory it limits
>> the guest VM to 1GB of memory even if I have more assigned to it at
>> startup. Has anybody else seen this? Is there something special about the
>> hotplug that this is expected that I'm not aware of?
>> Thanks,
>> Brian Hart
>> _______________________________________________
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>> pve-user at pve.proxmox.com
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