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Date: Fri, 14 Feb 2014 15:59:00 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] memory allocation of migration changed?
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To: Stefan Priebe <s.priebe@profihost.ag>
Cc: Orit Wasserman <owasserm@redhat.com>, Peter Lieven <pl@kamp.de>, qemu-devel <qemu-devel@nongnu.org>, Dave Gilbert <dgilbert@redhat.com>, Juan Quintela <quintela@redhat.com>

On Tue, Feb 11, 2014 at 07:32:46PM +0100, Stefan Priebe wrote:
> Am 11.02.2014 17:22, schrieb Peter Lieven:
> >
> >
> >>Am 11.02.2014 um 16:44 schrieb Stefan Hajnoczi <stefanha@gmail.com>:
> >>
> >>On Tue, Feb 11, 2014 at 3:54 PM, Stefan Priebe - Profihost AG
> >><s.priebe@profihost.ag> wrote:
> >>>in the past (Qemu 1.5) a migration failed if there was not enogh memory
> >>>on the target host available directly at the beginning.
> >>>
> >>>Now with Qemu 1.7 i've seen succeeded migrations but the kernel OOM
> >>>memory killer killing qemu processes. So the migration seems to takes
> >>>place without having anough memory on the target machine?
> >>
> >>How much memory is the guest configured with?  How much memory does
> >>the host have?
> >>
> >>I wonder if there are zero pages that can be migrated almost "for
> >>free" and the destination host doesn't touch.  When they are touched
> >>for the first time after migration handover, they need to be allocated
> >>on the destination host.  This can lead to OOM if you overcommitted
> >>memory.
> >>
> >>Can you reproduce the OOM reliably?  It should be possible to debug it
> >>and figure out whether it's just bad luck or a true regression.
> >>
> >>Stefan
> >
> >Kernel Version would also be interesting as well as thp and ksm settings.
> 
> Kernel Host: 3.10.26
> 
> What's thp / ksm? how to get those settings?

Transparent Huge Pages

# cat /sys/kernel/mm/transparent_hugepage/enabled

Kernel Samepage Merging

# cat /sys/kernel/mm/ksm/run

Stefan