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

[Andrew Morton]

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

> From: Steven Rostedt <srostedt@xxxxxxxxxx>
> 
> 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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