Subject: Re: [vserver] Running same process for each jail
From: Herbert Poetzl <herbert@13thfloor.at>
Date: Thu, 16 Oct 2008 13:02:25 +0200

On Tue, Oct 14, 2008 at 01:38:53AM +0100, Ed W wrote:
> Jun OKAJIMA wrote:
> >How about your opinion ?
> 
> This is also a question about how heavyweight you want your 
> virtualisation.  Many people won't settle for less than VMWare style 
> whole machine emulation and complete separation.  Vserver, et al are 
> much lighter weight still and your proposal is extremely lightweigth, 
> but hard to figure out how it could be implemented if multiple users are 
> involved...?
> 
> Simply hard linking all the similar jail files together will apparently 
> cause the non code pages to be loaded only once?

it will cause all the mappings (libraries and executables, as
well as read-only files) to be shared, because they will get
a mapping from the very same inode/cache

I doubt that you really want to share mappings of config
files, unless you are running redundant applications :)

> Note that if you share code pages between instances then you need to be 
> happy that any jail which can corrupt those pages gets to run code 
> across all jails... :-(

the important part is that the mappings are all read only
or copy on write at most, so affecting other guests across
a context is not possible (given you are using unification
and not just simple hardlinks :)

HTC,
Herbert

> Ed W