Open Stack

On 09/27/2017 04:55 PM, Blair Bethwaite wrote:
> Hi Prema
>
> On 28 September 2017 at 07:10, Premysl Kouril <premysl.kouril at gmail.com> wrote:
>> Hi, I work with Jakub (the op of this thread) and here is my two
>> cents: I think what is critical to realize is that KVM virtual
>> machines can have substantial memory overhead of up to 25% of memory,
>> allocated to KVM virtual machine itself. This overhead memory is not
>
> I'm curious what sort of VM configuration causes such high overheads,
> is this when using highly tuned virt devices with very large buffers?

For what it's worth we ran into issues a couple years back with I/O to 
RDB-backed disks in writethrough/writeback.  There was a bug that allowed a very 
large number of in-flight operations if the ceph server couldn't keep up with 
the aggregate load.  We hacked a local solution, I'm not sure if it's been dealt 
with upstream.

I think virtio networking has also caused issues, though not as bad.  (But 
noticeable when running close to the line.)

Chris