linux-kernel - Re: [PATCH 1/3] tracing: Remove dependency of saved_cmdlines_buffer on PID_MAX

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Date: Mon, 13 May 2024 19:30:49 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Christian Brauner <brauner@...nel.org>, Oleg Nesterov <oleg@...hat.com>, 
	Kent Overstreet <kent.overstreet@...ux.dev>, Kees Cook <keescook@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Tycho Andersen <tandersen@...flix.com>, 
	Jens Axboe <axboe@...nel.dk>, Aleksa Sarai <cyphar@...har.com>
Subject: Re: [PATCH 1/3] tracing: Remove dependency of saved_cmdlines_buffer
 on PID_MAX_DEFAULT

On Tue, Apr 09, 2024 at 11:01:26AM GMT, Steven Rostedt <rostedt@...dmis.org> wrote:
> > -	tpid = pid & (PID_MAX_DEFAULT - 1);
> > +	tpid = pid % PID_MAP_SIZE;
> 
> Does that compile to the same? This is a fast path.

I didn't check.
If fast is the intetion, I would change it to something
like BUILD_BUG_ON(!(PID_MAP_SIZE % 2)) and keep the bit operation
without reliance on compiler optimizations.

Thanks for the response (I may not follow up on this single commit
though).

Michal

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