Re: (pspace,pid) vs true pid virtualization

[ebiederm@xmission.com (Eric W. Biederman)]

Herbert Poetzl <herbert@13thfloor.at> writes:

> On Fri, Feb 17, 2006 at 03:57:26AM -0700, Eric W. Biederman wrote:
>> As for that.  When I mad that suggestion to Herbert Poetzl 
>> his only concern was that a smart init might be too heavy weight 
>> for lightweight vserver.  Generally I like the idea.
>
> well, may I remind that this solution would require _two_
> init processes for each guest, which could easily make up
> 300-400 unnecessary processes in a lightweight server
> setup?

I take it seriously enough that I remembered the concern,
and I think it is legitimate.  Figuring out how to safely
set the policy is a challenge.  That is something a
user space daemon trivially gets right.  

The kernel side of a process is about 10K if the user space
side was also lightweight we could have the entire
per process cost in the 30K range.  30K*400 = 12000K = 12M.

That is significant but we are still cheap enough that it
isn't necessarily a show stopper.

I think the cost was only one extra process, for the case where you
have fakeinit now it would be init, for other cases it would be a
daemon that gets setup when you initialize the vserver.

If we can get a permission checking model in the kernel right
it is potentially much cheaper, to have an enter model.

Having user space as a backup to that is still interesting.

>> > (Read the last sentence, and in case you're wondering, no I don't have
>> > any children in real life)
>> 
>> Speaking of that.  One of my coworkers mentioned that it is unfortunate
>> that our names don't have the double meaning.  So it was suggested we
>> call them 
>> 
>> Speaking of that problematic naming.  One of my coworkers mentioned that
>> it is unfortunate that our set of names does not have a double meaning.
>> After that the suggestion came up to call them families, instead of guest
>> or pidspaces.  Although I guess calling them guests is about as bad :)
>
> well, at least Guests or VEs are terms already used by
> existing projects, where pspace sounds somewhat strange.
>
> at the same time I'd like to point out that *spaces is
> a good name for the building blocks, but we definitely
> have to name the 'construct' different, i.e. a 'guest'
> (or VPS or VE or whatever) is _more_ than just a p-space
> it's the sum of all *-spaces required to make it look
> like a real linux system.

I totally agree.  Sorry.  This was meant as a humerous tangent!
I thought the smiley and the fact I was looking for a name
with a double meaning that would have made it easier to get
confused would have made that clear!

Oh well such is confusion an email :)

Eric
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