Re: [Qemu-devel] Memory sync algorithm during migration

[Takuya Yoshikawa]

Adding qemu-devel ML to CC.

Your question should have been sent to qemu-devel ML because the logic
is implemented in QEMU, not KVM.

(2011/11/11 1:35), Oliver Hookins wrote:
> Hi,
>
> I am performing some benchmarks on KVM migration on two different types of VM.
> One has 4GB RAM and the other 32GB. More or less idle, the 4GB VM takes about 20
> seconds to migrate on our hardware while the 32GB VM takes about a minute.
>
> With a reasonable amount of memory activity going on (in the hundreds of MB per
> second) the 32GB VM takes 3.5 minutes to migrate, but the 4GB VM never
> completes. Intuitively this tells me there is some watermarking of dirty pages
> going on that is not particularly efficient when the dirty pages ratio is high
> compared to total memory, but I may be completely incorrect.

You can change the ratio IIRC.
Hopefully, someone who knows well about QEMU will tell you better ways.

        Takuya

> Could anybody fill me in on what might be going on here? We're using libvirt
> 0.8.2 and kvm-83-224.el5.centos.1
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