Subject: Re: [vserver] Pros and Cons of 32/64bit guests on 64bit host
From: Stephen Liu <satimis@yahoo.com>
Date: Fri, 22 Aug 2008 22:38:54 +0800 (CST)


--- Ed W <lists@wildgooses.com> wrote:


> >> With KVM you can overcommit, as with others I believe, ie for you
> 8GB
> >> machine 
> >> you can have 4 VMs with 4GB each; physical RAM will get used
> >> according to 
> >> each VM's usage.
> >>     
> >
> >
> > Sorry I don't follow.  If 4 VMs (not KVM/QEMU) with 4G each then I
> need
> > 16G RAM at least.
> >   
> 
> 
> Only if they all use 4G at the same time
> 
> It's common for a machine to be largely idle, so for example you may 
> find that the working set is only 100MB despite nominally using 4G.  
> This makes it possible to page out most of the instance and require a
> 
> lot less ram.  You are suddenly stuffed big time though if all your 
> machines suddenly come alive and need their ram back...
> 
> I think overcommit can be handled slightly more neatly with vservers 
> because effectively it's just a bunch of processes which are running
> in 
> one operating system with a bit of a partition between them.


Noted and thanks


B.R.
Stephen L

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