Re: [MirageOS-devel] Memory requirements for a typical Mirage OS VM

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

On 23 Feb 2014, at 12:57, Lars Kurth <lars.kurth@xxxxxxx> wrote:

> On 22/02/2014 22:29, Richard Mortier wrote:
>> On 22 Feb 2014, at 22:13, Julian Chesterfield 
>> <julian.chesterfield@xxxxxxxxx> wrote:
>> 
>>> So hosting the website image will require more ram than a minimal image.
>> yes; hence my question about what "typical" means :)
> The background for the question was whether the event channel improvements in 
> Xen 4.4 (and thus the capability to run a lot of smaller VMs on one host) 
> will benefit Mirage OS and others. That argement hinges on Mirage OS (and 
> similar) having significantly smaller memory footprints that your traditional 
> VM.
> 
> I guess "typical" means "memory requirements for the type of workloads Mirage 
> OS is aiming to target

They definitely will have a big positive impact.  Our overall goal is to get an 
equivalent number of MirageOS VMs running as you can get distinct processes 
running on a single Unix host.  If most are idle (e.g. just brief amount of 
traffic) and we are using modern 64-core machines, then we've estimated that we 
able to get to 10000 VMs without too many problems, with these problems rearing 
their head:

- RAM utilization (given 24MB is right on the edge, so page sharing is needed)
- page sharing between similar VMs will help reduce load
- that many VMs would require driver domains, since a dom0 is very unlikely to 
be able to handle all the load.
- the VM scheduler may come under some pressure

The "10000 VM" goal is a stake in the ground to see how well the Xen 
architecture holds up to very dense clouds of tiny VMs, and it was really 
blocked on the low event channel number that existed in Xen 4.4+.

cheers,
Anil
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