[dundee] VMWare Server 2.0

[Lee Hughes]

just reading about vmware, it says it need 
   'needs proprietary kernel modules'

I don't like the sound of that ;-).

Thing that gets me about virtual machines is memory usage, it all well and good on
a single machine (non vm)  you can have say 1GB of ram and setup 2GB of swap space,
but linux seems rather lazy about claiming and reclaiming memory, if I look at my own
machine I have 1GB of ram,  and currently using 787MB of swap! This would cause
havoc in a virtual environment.... okay I need a memory upgrade.

Until linux applications constrain their memory use , or they can be given hints on
maximum or minimum  memory use then using any virtual machine technology that
support paging to disk, is a no no.

paging to disk is not usually a bit problem, as only one machine is effected, and that
machine has already exhausted it's memory  , so a slow down is expected. Misbehaving
VM's that are paging will effect performance of all vm's on that system.

Take Apache for example, this always seems to grow in size, it will fork() more depending
on it's load, using more memory in the process, I've never seen it release memory ,
unless you restart the entire process. :-(. Obviously you can tune it, but be great
if this, and other app were aware they we're being virtualised, and tuned their memory
allocation accordingly..
.
So, perhaps applications should become more vm aware? Programmers should stop thinking that memory is infiite resources, and stop assuming that if they allocate more memory than is available then, the kernel/libc will just 'sort it out for them'. Memory leaks on
one vm's app's could potential effect others.. 

Linux still suffers from memory leaks , they get fixed, I was told once that the unix
mount command leaks lots of memory, sure you only ever run it, it does it job
and it quits (linux then reclaims memory) but that's not excuse for sloppy code.

Java VM seems a bit more promising, at least you can force garbage collection in
low memory situations.

But what is the solution to this, large disk administrators setup up temp area's, where
users can create very large working files but for a limited amount of time? Perhaps
this needs to be implemented in memory management too?  Okay, mr apache you can
double your memory size for but only for x amount of time.

Openvz seems to stay away from virtual memory, and allows you you to allocate
min and max pages, but it's rather a black magic  do with your wetting your
finger and putting it the air.

For my installed I've just pack as much ram as possible in , to avoid unnecessary swapping.

I'd be interested about commercial vm solutions, do they have a magic bullet for
memory management?




























 








--- On Wed, 1/10/08, gordon dunlop <astrozubenel at googlemail.com> wrote:
From: gordon dunlop <astrozubenel at googlemail.com>
Subject: Re: [dundee] VMWare Server 2.0
To: toxicnaan at yahoo.co.uk, "Tayside Linux User Group" <dundee at lists.lug.org.uk>
Date: Wednesday, 1 October, 2008, 8:31 AM

2008/9/30 Lee Hughes <toxicnaan at yahoo.co.uk>:
> well, Gordon, you can't sell me on vmware,

Lee I am not trying to sell anybody anything, when it comes to which
virtualisation technology to use it is horses for courses i.e. user
requirements. I am just noticing the rapid improvement in the free
offerings that VMWare are giving out (due to virtualisation
competition hotting up). Red Hat have recently bought Qumranet, the
company behind KVM which is in the Linux kernel. Whilst Xen is the
virtualisation technology of choice for Red Hat, the rationale behind
this acquisition is to maintain the open source nature of KVM and to
develop it within the Linux kernel. So as KVM development improves its
functionality, there will be a time when there is a total Linux kernel
virtualisation solution and no-one will really need Virtual Box,
VMWare or Xen. A couple of years ago there was talk of having Xen and
OpenVZ fully implemented within the Linux kernel, whilst there are
large chunks of code from Xen and OpenVZ within the Linux kernel, this
has never happened.

Gordon





> Cheers,
> Lee
> 'your reality is my virtual machine'
>
>
>
>

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