linux-kernel - Re: [PATCH] tracing: Have saved_cmdlines arrays all in one allocation

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Date: Tue, 13 Feb 2024 08:35:22 -0800
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>,  Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Mark Rutland <mark.rutland@....com>, Vincent Donnefort
 <vdonnefort@...gle.com>, Sven Schnelle <svens@...ux.ibm.com>, Mete Durlu
 <meted@...ux.ibm.com>
Subject: Re: [PATCH] tracing: Have saved_cmdlines arrays all in one
 allocation

On Mon, 2024-02-12 at 19:13 -0500, Steven Rostedt wrote:
> On Mon, 12 Feb 2024 15:39:03 -0800
> Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> 
> > > diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
> > > index e4fbcc3bede5..210c74dcd016 100644
> > > --- a/kernel/trace/trace_sched_switch.c
> > > +++ b/kernel/trace/trace_sched_switch.c
> > > @@ -201,7 +201,7 @@ static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)
> > >  	int order;
> > >  
> > >  	/* Figure out how much is needed to hold the given number of cmdlines */
> > > -	orig_size = sizeof(*s) + val * TASK_COMM_LEN;
> > > +	orig_size = sizeof(*s) + val * (TASK_COMM_LEN + sizeof(int));  
> > 
> > Strictly speaking, *map_cmdline_to_pid is unsigned int so it is more consistent
> > to use sizeof(unsigned) in line above.  But I'm nitpicking and I'm fine to
> > leave it as is.
> 
> I was thinking about making that into a macro as it is used in two places.
> 
> /* Holds the size of a cmdline and pid element */
> #define SAVED_CMDLINE_MAP_ELEMENT_SIZE(s)		\
> 	(TASK_COMM_LEN + sizeof((s)->map_cmdline_to_pid[0]))
> 
> 	orig_size = sizeof(*s) + val * SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
> 
> 

Looks good. This makes the code more readable.

Tim