Re: How much of a mess does OpenVZ make? ;) Was: What can OpenVZ do?

* Alexey Dobriyan [off-list ref] wrote:

On Fri, Mar 13, 2009 at 02:01:50PM -0700, Linus Torvalds wrote:

quoted

On Fri, 13 Mar 2009, Alexey Dobriyan wrote:

quoted

quoted

Let's face it, we're not going to _ever_ checkpoint any 
kind of general case process. Just TCP makes that 
fundamentally impossible in the general case, and there 
are lots and lots of other cases too (just something as 
totally _trivial_ as all the files in the filesystem 
that don't get rolled back).

What do you mean here? Unlinked files?

Or modified files, or anything else. "External state" is a 
pretty damn wide net. It's not just TCP sequence numbers and 
another machine.

I think (I think) you're seriously underestimating what's 
doable with kernel C/R and what's already done.

I was told (haven't seen it myself) that Oracle installations 
and Counter Strike servers were moved between boxes just fine.

They were run in specially prepared environment of course, but 
still.

That's the kind of stuff i'd like to see happen.

Right now the main 'enterprise' approach to do 
migration/consolidation of server contexts is based on hardware 
virtualization - but that pushes runtime overhead to the native 
kernel and slows down the guest context as well - massively so.

Before we've blinked twice it will be a 'required' enterprise 
feature and enterprise people will measure/benchmark Linux 
server performance in guest context primarily and we'll have a 
deep performance pit to dig ourselves out of.

We can ignore that trend as uninteresting (it is uninteresting 
in a number of ways because it is partly driven by stupidity), 
or we can do something about it while still advancing the 
kernel.

With containers+checkpointing the code is a lot scarier (we 
basically do system call virtualization), the environment 
interactions are a lot wider and thus they are a lot more 
difficult to handle - but it's all a lot faster as well, and 
conceptually so. All the runtime overhead is pushed to the 
checkpointing step - (with some minimal amount of data structure 
isolation overhead).

I see three conceptual levels of virtualization:

 - hardware based virtualization, for 'unaware OSs'

 - system call based virtualization, for 'unaware software'

 - no virtualization kernel help is needed _at all_ to 
   checkpoint 'aware' software. We have libraries to checkpoint 
   'aware' user-space just fine - and had them for a decade.

	Ingo

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