linux-kernel - Re: [PATCH 4/4] ring-buffer: only allocate buffers for online cpus

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Date:	Wed, 11 Mar 2009 20:32:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Pierre Ossman <drzeus@...eus.cx>, Pekka Paalanen <pq@....fi>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 4/4] ring-buffer: only allocate buffers for online cpus

On Wed, 11 Mar 2009 22:37:24 -0400 Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <srostedt@...hat.com>
> 
> Impact: save on memory
> 
> Currently, a ring buffer was allocated for each "possible_cpus". On
> some systems, this is the same as NR_CPUS. Thus, if a system defined
> NR_CPUS = 64 but it only had 1 CPU, we could have possibly 63 useless
> ring buffers taking up space. With a default buffer of 3 megs, this
> could be quite drastic.
> 
> This patch changes the ring buffer code to only allocate ring buffers
> for online CPUs.  If a CPU goes off line, we do not free the buffer.
> This is because the user may still have trace data in that buffer
> that they would like to look at.
> 
> Perhaps in the future we could add code to delete a ring buffer if
> the CPU is offline and the ring buffer becomes empty.
> 
> ...
>
> +#ifdef CONFIG_HOTPLUG
> +#ifdef CONFIG_HOTPLUG
> +#ifdef CONFIG_HOTPLUG
> +#ifdef CONFIG_HOTPLUG
> +#ifdef CONFIG_HOTPLUG

CONFIG_HOTPLUG_CPU
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