Re: Swap usage with KVM

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

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On Sunday, 11 July 2010 19:08:58 -0300,
Daniel Bareiro 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.

This is a current measurement I've taken in both the VMs and in VMHost:

* VMHost:


ss04:~# free
             total       used       free     shared    buffers     cached
Mem:      16461588   16405140      56448          0       3496      18604
-/+ buffers/cache:   16383040      78548
Swap:      5174220    2401552    2772668


* Aps4:

aps4:~# free
             total       used       free     shared    buffers     cached
Mem:       7164300    7120192      44108          0      23108     239076
-/+ buffers/cache:    6858008     306292
Swap:      2931820      14084    2917736


* Leela:

leela:~# free
             total       used       free     shared    buffers     cached
Mem:       7163836    6905224     258612          0     123380    6282816
-/+ buffers/cache:     499028    6664808
Swap:       979924      35640     944284


As you can see, I added more swap in VMHost for more margin, but
currently only 54% is free.



Thanks in advance for your replies.

Regards,
Daniel
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