linux-kernel - Re: [PATCH v3] printk: allow increasing the ring buffer depending on the number of CPUs

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Date:	Fri, 13 Jun 2014 14:41:52 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	hpa@...ux.intel.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Michal Hocko <mhocko@...e.cz>, Petr Mladek <pmladek@...e.cz>,
	Joe Perches <joe@...ches.com>,
	Arun KS <arunks.linux@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Chris Metcalf <cmetcalf@...era.com>
Subject: Re: [PATCH v3] printk: allow increasing the ring buffer depending
 on the number of CPUs

On Fri, 2014-06-13 at 11:28 -0700, Luis R. Rodriguez wrote:
> +	/*
> +	 * If you set log_buf_len=n kernel parameter LOG_CPU_MIN_BUF_SHIFT will
> +	 * be ignored. LOG_CPU_MIN_BUF_SHIFT is a proactive measure for large
> +	 * systems. With a LOG_BUF_SHIFT of 18 and LOG_CPU_MIN_BUF_SHIFT 12 at
> +	 * we'd require more than 64 CPUs to trigger an increase from the
> +	 * default.
> +	 */
> +	if (!new_log_buf_len && (cpu_extra > __LOG_BUF_LEN / 2))
             ^ that ! looks wrong. We should be checking for log_buf_len set instead.

> +		new_log_buf_len = __LOG_BUF_LEN + cpu_extra;

You could also move the whole thing below the return statement, that way
we can avoid double checking new_log_buf_len. Otherwise looks kinda
weird.
>  
>  	if (!new_log_buf_len)
>  		return;

Thanks,
Davidlohr

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