Re: [Qemu-devel] is there a limit on the number of in-flight I/O operations?

[Andrey Korolyov]

On Fri, Jul 18, 2014 at 6:58 PM, Chris Friesen
<address@hidden> wrote:
> Hi,
>
> I've recently run up against an interesting issue where I had a number of
> guests running and when I started doing heavy disk I/O on a virtio disk
> (backed via ceph rbd) the memory consumption spiked and triggered the
> OOM-killer.
>
> I want to reserve some memory for I/O, but I don't know how much it can use
> in the worst-case.
>
> Is there a limit on the number of in-flight I/O operations?  (Preferably as
> a configurable option, but even hard-coded would be good to know as well.)
>
> Thanks,
> Chris
>

Hi, are you using per-vm cgroups or it was happened on bare system?
Ceph backend have writeback cache setting, may be you hitting it but
it must be set enormously large then.