Re: Swap usage with KVM

[Daniel Bareiro <daniel-listas@gmx.net>]

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Hi, Freddie.

On Sunday, 11 July 2010 14:05:38 -0700,
Freddie Cash wrote:

> > I have an installation with Debian GNU/Linux 5.0.4 amd64 with
> > qemu-kvm 0.12.3 compiled with the source code obtained from the
> > official site of KVM and Linux 2.6.32.12 compiled from source code
> > of kernel.org. All this is installed on an HP Proliant DL380 G6 with
> > two Xeon E5530 quadcore processors and 16 GiB of RAM which has two
> > VMs with the following configuration of memory:

> Are you using virtio drivers in the VMs?
> 
> There was an issue with KVM-72 and virtio that leaks memory in the
> host until all RAM and swap is used (inside the VMs, no swap is used).
> It was supposed to be fixed in KVM-80-something, though.
> 
> Perhaps something similar is happening again?  If you switch the disks
> to scsi instead of virtio, does the problem go away?
> 
> We are running KVM-72 on Debian 5.0 and have run into this issue.
> We'll be upgrading our hosts this month to fix this.

Yes, we are using Virtio drivers for networking and storage in both VMs
with cache=none. Both VMs are running Linux 2.6.32-bpo.5-amd64 from
Lenny Backports repositories. For VMHost, we are using a stable version
of KVM with Linux 2.6.32.12 compiled from source code of kernel.org and
qemu-kvm 0.12.3 compiled with the source code obtained from the official
site of KVM.

This is the syntax I'm using to boot the virtual machines:


 8587 ?        Sl   6515:25 /usr/local/qemu-kvm/bin/qemu-system-x86_64 -drive
file=/dev/vm/aps4-raiz,cache=none,if=virtio,boot=on -drive
file=/dev/vm/aps4-cache,cache=none,if=virtio -drive file=/dev/vm/aps4-index,cache=none,if=virtio
-drive file=/dev/vm/aps4-space,cache=none,if=virtio -m 7168 -smp 4 -net
nic,model=virtio,macaddr=00:16:3e:00:00:95 -net tap -daemonize -vnc :3 -k es -localtime -monitor
telnet:localhost:4003,server,nowait -serial telnet:localhost:4043,server,nowait

 9769 ?        Rl   11968:47 /usr/local/qemu-kvm/bin/qemu-system-x86_64 -drive
file=/dev/vm/leela-raiz,cache=none,if=virtio,boot=on -drive
file=/dev/vm/leela-u01,cache=none,if=virtio -drive file=/dev/vm/leela-u02,cache=none,if=virtio
-drive file=/dev/vm/leela-u03,cache=none,if=virtio -drive
file=/dev/vm/leela-u04,cache=none,if=virtio -drive file=/dev/vm/leela-u05,cache=none,if=virtio
-drive file=/dev/vm/leela-u06,cache=none,if=virtio -drive
file=/dev/vm/leela-u07,cache=none,if=virtio -drive file=/dev/vm/leela-u08,cache=none,if=virtio
-drive file=/dev/vm/leela-u09,cache=none,if=virtio -drive
file=/dev/vm/leela-space,cache=none,if=virtio -m 7168 -smp 8 -net
nic,model=virtio,macaddr=00:16:3e:00:00:96 -net tap -daemonize -vnc :4 -k es -localtime -monitor
telnet:localhost:4004,server,nowait -serial telnet:localhost:4044,server,nowait


To make the switch from Virtio to SCSI I would have to shut down the
hosts, which would not be a good idea whereas are two productive
systems. At least, before doing so I would be sure of what might be the
problem.

Taking a current measurement in VMHost with free, I got the following:


ss04:~# free
             total       used       free     shared    buffers     cached
Mem:      16461588   16406504      55084          0       2920      21504
-/+ buffers/cache:   16382080      79508
Swap:      2028492     983140    1045352


It draws attention to me that thinking about initially leaving a margin
of 2 GB of RAM for the VMHost, already it has used almost half of swap.


Thanks for your reply.

Regards,
Daniel
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