linux-kernel - Re: [PATCH] Mark timer_stats as incompatible with multiple pid namespaces

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Date:	Thu, 13 Dec 2007 22:37:11 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Mark timer_stats as incompatible with multiple pid
	namespaces


* Eric W. Biederman <ebiederm@...ssion.com> wrote:

> >> Well struct pid * works in that case if you grab the reference to 
> >> it.
> >
> > but the display of the stats might happen much later. The point of 
> > this API is to save pid+comm, which gives users a good idea about 
> > what caused the events in the past - without having to pin any 
> > resource of that task.
> 
> Likewise struct pid is designed not to be a problem if pinned. It is a 
> little heavier then it used to be with the addition of pid namespace 
> support but not much.  And if it is to heavy struct pid needs to be 
> fixed.
> 
> Holding the struct pid very much does not pin the task struct, and it 
> shouldn't pin any other resources.  I agree 64bytes or so is a bit 
> more to pin then 4 bytes but it really isn't a lot.

yeah, and i have no conceptual objections - i just wanted to outline the 
thinking behind /proc/timer_stats.

	Ingo
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