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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 05/16] tracing: show that buffer size is not expanded
Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <peterz@infradead.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Lai Jiangshan <laijs@cn.fujitsu.com>,
       Steven Rostedt <srostedt@redhat.com>
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Date: Fri, 13 Mar 2009 12:05:53 +0900 (JST)
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> From: Steven Rostedt <srostedt@redhat.com>
> 
> Impact: do not confuse user on small trace buffer sizes
> 
> When the system boots up, the trace buffer is small to conserve memory.
> It is only two pages per online CPU. When the tracer is used, it expands
> to the default value.
> 
> This can confuse the user if they look at the buffer size and see only
> 7, but then later they see 1408.
> 
>  # cat /debug/tracing/buffer_size_kb
> 7
> 
>  # echo sched_switch > /debug/tracing/current_tracer
> 
>  # cat /debug/tracing/buffer_size_kb
> 1408
> 
> This patch tries to help remove this confustion by showing that the
> buffer has not been expanded.
> 
>  # cat /debug/tracing/buffer_size_kb
> 7 (expanded: 1408)

Hi,

I have one question.
Why souldn't use following output?

sprintf(buf, "%lu\n", trace_buf_size >> 10);


My point is:
  - pure number output can hadle easily.
  - nobody need to know internal memory saving logic.