[Qemu-devel] creating vm fails if maxMemory equals to memory, but hotplug same will success

[Qemu-devel] creating vm fails if maxMemory equals to memory, but hotplug same will success

[Yi Wang]

Hi, all
When I create a vm using virsh, it will fail if maxMemory(2G) equals
to memory(2G) in XML:
error: Failed to create domain from vm1.xml
error: internal error: process exited while connecting to monitor:
qemu-kvm: -msg timestamp=on: invalid value of -m option maxmem: memory
slots were specified but maximum memory size (0x80000000) is equal to
the initial memory size (0x80000000)

However, if I allocate 1G memory for the guest at boot time(maxMemory
is still 2G), and then hotplug 1G to it, and it will success! Now
total memory is 2G and it equals to maxMemory. Is this a bug? if so, I
would be happy to work on a patch to fix this. Please tell me how this
designs if this is not a bug.

Thanks a lot.

-- 
Best Regards
Yi Wang

Re: [Qemu-devel] creating vm fails if maxMemory equals to memory, but hotplug same will success

[Igor Mammedov]

On Wed, 7 Oct 2015 23:29:07 +0800
Yi Wang <up2wing@gmail.com> wrote:

> Hi, all
> When I create a vm using virsh, it will fail if maxMemory(2G) equals
> to memory(2G) in XML:
> error: Failed to create domain from vm1.xml
> error: internal error: process exited while connecting to monitor:
> qemu-kvm: -msg timestamp=on: invalid value of -m option maxmem: memory
> slots were specified but maximum memory size (0x80000000) is equal to
> the initial memory size (0x80000000)
-m initial_memory[,slots=X,maxmem=Y]

By design 'initial_memory' is not hotplugable and slots,maxmem should be
used if hotplug is needed and maxmem should be greater than initial_memory.
There isn't point specifying maxmem == initial_memory (i.e. 0-sized hotplug
space) and that's what QEMU is complaining about.

> 
> However, if I allocate 1G memory for the guest at boot time(maxMemory
> is still 2G), and then hotplug 1G to it, and it will success! Now
> total memory is 2G and it equals to maxMemory. Is this a bug? if so, I
> would be happy to work on a patch to fix this. Please tell me how this
> designs if this is not a bug.
> 
> Thanks a lot.
>