Well, I just tried disabling smp on my guest, and live migration worked
fine. I see that there are already SMP complaints with live migration in
KVM:84 in the bug database, so I guess this is just another, "Me, too."
Is this expected to be fixed in the soon-to-be-released KVM:85?
Thanks,
Brent
PS The migrated guest still uses its full memory allocation, even though
the original was nowhere close.
PPS The perceptible delay in an open ssh session was similar between the
live and offline migrations. I guess this is beyond KVMs control, though,
and more dependent on how quickly gratuitous arp is being handled, or
something else to do with the transition of the IP/MAC between nodes.
It's just a handful of seconds, either way.
On Fri, 17 Apr 2009, Brent A Nelson wrote:
I, too, am trying out the KVM 84 build for Hardy. I didn't have any problems
with networking (I'm using a bridge interface), except I had to specify
script=/etc/kvm/kvm-ifup, unlike with KVM 62. Without specifying any
script=, kvm looks for /etc/kvm-ifup, which does not exist. Perhaps this is
just a glitch with the way the Ubuntu folks built the package.
However, live migration simply doesn't work right. When it completes, the
migrated guest always immediately crashes in some fashion (I've had an oops,
a panic, and a reboot). I can send the original a "cont" command, however,
and it will resume as if nothing had happened.
If I first stop the guest, then migration works great, and it's fast enough
to hardly notice the brief unresponsiveness. However, there's a nuisance
here, too. The migrated VM uses the full amount of memory allocated to it,
even though the original may have been using only a small fraction. I tried
issuing a balloon command to shrink it; the guest VM did see the smaller
memory size, but the kvm process itself did not change memory consumption.
When I used the balloon command to set it back to the original, full size,
the guest VM saw its memory shrink down to nothing until all processes had
been killed by the out-of-memory killer.
"info balloon" tells me:
Using KVM without synchronous MMU, ballooning disabled
So, I assume I don't have everything I need to try ballooning properly to see
if I can reduce the excess memory consumed by the migrated guest VM.
Thanks,
Brent Nelson
Director of Computing
Dept. of Physics
University of Florida
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