linux-kernel - Re: [PATCH 0/16] Pid namespaces

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Date:	Mon, 09 Jul 2007 12:58:37 -0700
From:	Dave Hansen <haveblue@...ibm.com>
To:	Pavel Emelianov <xemul@...nvz.org>
Cc:	Andrew Morton <akpm@...l.org>, Kirill Korotaev <dev@...nvz.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Containers <containers@...ts.osdl.org>
Subject: Re: [PATCH 0/16] Pid namespaces

On Mon, 2007-07-09 at 09:58 +0400, Pavel Emelianov wrote:
> Dave Hansen wrote:
> > On Fri, 2007-07-06 at 12:01 +0400, Pavel Emelianov wrote:
> >> This is "submition for inclusion" of hierarchical, not kconfig
> >> configurable, zero overheaded ;) pid namespaces.
> > 
> > Pavel, I'm a bit disappointed that you went ahead and sent this.  I
> > thought that, perhaps, you might have brought up how displeased you were
> > with Suka's patches when we discussed them at OLS.  
> > 
> > Hold your horses there a bit.  This has "little" overhead for the common
> > case, which is a single level of pid namespaces.  That means that it is
> > quick to access the "global" pid which would be the one that the "host
> > container" sees.  It also provides quick access to the pid which a
> > containerized task gets when the task itself calls getpid().  This quick
> > access is provided by storing the values directly in the task struct.
> > 
> > However, when there is more than one level in the container hierarchy,
> > the optimization breaks down.  A process which exists in a three-level
> > hierarchy has slow access to the middle level pid.  Your approach stores
> > this information in a linked list, and surely *that* is going to have
> 
> No. This approach stores numerical values in array. I have
> removed the lists at all.

Ahh.  I was confused by the hlist in 'struct pid'.  You are very correct.

Suka actually coded up something very, very similar to what you have.  I
just made him remove some of it so that the patches could be more easily
reviewed.  I figured we could add the fully dynamic allocation later,
which you have already done.  That part of your patches is remarkably
similar.  

-- Dave

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