[libvirt-users] vm live migration memory copy

[Martin Kletzander]

On Sun, Jun 04, 2017 at 11:43:35AM +0200, Hui Jing wrote:
>Hi All,
>
>I am wondering when we do live migration, how much memory is transferred? I
>guess it must be one of the three below, but not sure which one:
>1. The amount of memory allocated to VM
>2. The memory currently used by VM (actual Mem usage in guest)
>3. The memory used by the qemu process (RSS).
>

It is more complicated than that.  You need to transfer all the memory
that the VM used, that's for sure, right?  Then it depends on the
hypervisor whether or not they include the nulls, how much of their
memory they need transfer, how much memory is there for all the devices
that the VM has, whether there's any compression algorithm applied, and,
most importantly, you need to retransfer any memory that was changed
after it was transferred.  And when you are re-transferring, the same
can happen.  So at the end it depends on how fast your guest is changing
how much memory and how fast your transfer is.  Plus bunch of other
things that I forgot, for sure.

>Best Regards,
>Hui

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