From: Andi Kleen <ak@suse.de>
To: "Serge E. Hallyn" <serue@us.ibm.com>
Subject: Re: [PATCH 7/7] uts namespaces: Implement CLONE_NEWUTS flag
Date: Tue, 2 May 2006 19:30:44 +0200
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On Tuesday 02 May 2006 19:20, Serge E. Hallyn wrote:
> Quoting Andi Kleen (ak@suse.de):
> > On Tuesday 02 May 2006 10:03, Eric W. Biederman wrote:
> > 7 additional bits will probably not be enough. I still don't
> > quite understand why you want individual bits for everything.
> > Why not group them into logical pieces? 
> 
> I wouldn't be surprised if it makes sense to combine some of them.  For
> instance, perhaps utsname and networking?

I frankly would just combine everything new.

> 
> > Have a proxy structure which has pointers to the many name spaces and a bit
> > mask for "namespace X is different".
> 
> different from what?

>From the parent.

> 
> Oh, you mean in case we want to allow cloning a namespace outside of
> fork *without* cloning the nsproxy struct?

Basically every time any name space changes you need a new nsproxy.

> 
> > This structure would be reference
> > counted. task_struct has a single pointer to it.
> 
> If it is reference counted, that implies it is shared between some
> processes.  But namespace pointers themselves are shared between some of
> these nsproxy's.  The lifetime mgmt here is one reason I haven't tried a
> patch to do this.

The livetime management is no different from having individual pointers.

> > With many name spaces you would have smaller task_struct, less cache 
> > foot print, better cache use of task_struct because slab cache colouring
> > will still work etc.
> 
> I suppose we could run some performance tests with some dummy namespace
> pointers?  9 void *'s directly in the task struct, and the same inside a
> refcounted container struct.  The results might add some urgency to
> implementing the struct nsproxy.

Not sure you'll notice too much difference on the beginning. I am just
the opinion memory/cache bloat needs to be attacked at the root, not
when it's too late.

-Andi
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