linux-kernel - Re: [RFC PATCH v4] Unified trace buffer

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Date:	Thu, 25 Sep 2008 21:52:45 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC PATCH v4] Unified trace buffer

Hi Steven,

Steven Rostedt wrote:
> This version has been cleaned up a bit. I've been running it as
> a back end to ftrace, and it has been handling pretty well.

Thank you for your great work.
It seems good to me(especially, encapsulating events :)).

I have one request of enhancement.

 > +static struct ring_buffer_per_cpu *
 > +ring_buffer_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
 > +{
[...]
 > +	cpu_buffer->pages = kzalloc_node(ALIGN(sizeof(void *) * pages,
 > +					       cache_line_size()), GFP_KERNEL,
 > +					 cpu_to_node(cpu));

Here, you are using a slab object for page managing array,
the largest object size is 128KB(x86-64), so it can contain
16K pages = 64MB.

As I had improved relayfs, in some rare case(on 64bit arch),
we'd like to use larger buffer than 64MB.

http://sourceware.org/ml/systemtap/2008-q2/msg00103.html

So, I think similar hack can be applicable.

Would it be acceptable for the next version?

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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