linux-kernel - Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun field

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Date:	Tue, 18 Nov 2008 16:50:45 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun
	field


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Tue, 18 Nov 2008, Ingo Molnar wrote:
> > > > 
> > > > that reminds me: ti->ret_stack[] should be moved to task->ret_stack[]. 
> > > > That way we decouple its size from any kernel stack size limits. 
> > > > (thread-info resides at one end of the kernel stack, on x86)
> > > 
> > > Yeah, I recommended that to Frederic to save space. But that can be 
> > > dangerous. Using task instead would be safer with the downside of 
> > > making the task struct even bigger.
> > 
> > We almost never put new stuff into thread_info - we have the 
> > lockdep lock stack in the task structure too, for similar reasons.
> 
> Yeah, it was just a recommendation, and perhaps not a good one ;-)
> 
> Frederic, it is better if you move the array from the thread info to 
> the task struct. It will take up more memory but it is a hell of a 
> lot safer. The pro here definitely outways the con.

if the memory footprint starts mattering we could turn this into a 
single pointer to an array - and add/remove these arrays (from all 
tasks currently running) as the tracer is turned on/off.

	Ingo
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