linux-kernel - Re: [RFC][PATCH] tracepoint: Do not waste memory on mods with no tracepoints

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Date:	Thu, 27 Feb 2014 11:00:35 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] tracepoint: Do not waste memory on mods with no tracepoints

Steven Rostedt <rostedt@...dmis.org> writes:
> No reason to allocate tp_module structures for modules that have no
> tracepoints. This just wastes memory.
>
> Fixes: b75ef8b44b1c "Tracepoint: Dissociate from module mutex"
> Cc: stable@...r.kernel.org # 3.2+

Really?  CC:stable?  To save an insignificant amount of memory?

The definition of stable seems to be shifting away from "fixes for
problems with significant effects".  I obviously missed the memo.

Rusty.



> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  kernel/tracepoint.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 29f2654..0d4ef26 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -636,6 +636,9 @@ static int tracepoint_module_coming(struct module *mod)
>  	struct tp_module *tp_mod, *iter;
>  	int ret = 0;
>  
> +	if (!mod->num_tracepoints)
> +		return 0;
> +
>  	/*
>  	 * We skip modules that taint the kernel, especially those with different
>  	 * module headers (for forced load), to make sure we don't cause a crash.
> @@ -679,6 +682,9 @@ static int tracepoint_module_going(struct module *mod)
>  {
>  	struct tp_module *pos;
>  
> +	if (!mod->num_tracepoints)
> +		return 0;
> +
>  	mutex_lock(&tracepoints_mutex);
>  	tracepoint_update_probe_range(mod->tracepoints_ptrs,
>  		mod->tracepoints_ptrs + mod->num_tracepoints);
> -- 
> 1.8.1.4
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