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

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Message-ID: <c62985530811180831n132ed6dep77aa2684ff59861@mail.gmail.com>
Date:	Tue, 18 Nov 2008 17:31:37 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Steven Rostedt" <rostedt@...dmis.org>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun field

2008/11/18 Ingo Molnar <mingo@...e.hu>:
>
> * 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
>

Ok. So what do you suggest once? Do I begin to move the array from
thread info to struct task but by keeping the static
array or should I directly use a dynamic allocation and add/remove dynamically?
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