linux-kernel - Re: [RFC 12/12] x86/dumpstack: Optimize save_stack

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Date:	Fri, 1 Jul 2016 08:06:08 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	xinhui <xinhui.pan@...ux.vnet.ibm.com>
Cc:	peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, npiggin@...e.de, walken@...gle.com,
	ak@...e.de
Subject: Re: [RFC 12/12] x86/dumpstack: Optimize save_stack_trace

On Thu, Jun 30, 2016 at 06:38:47PM +0800, xinhui wrote:
> >>>>+static int save_stack_end(void *data)
> >>>>+{
> >>>>+	struct stack_trace *trace = data;
> >>>>+	return trace->nr_entries >= trace->max_entries;
> >>>>+}
> >>>>+
> >>>>   static const struct stacktrace_ops save_stack_ops = {
> >>>>   	.stack		= save_stack_stack,
> >>>>   	.address	= save_stack_address,
> >>>then why not check the return value of ->address(), -1 indicate there is
> >>>no room to store any pointer.
> >>
> >>Hello,
> >>
> >>Indeed. It also looks good to me even though it has to propagate the condition
> >>between callback functions. I will modify it if it's better.
> >
> >Do you also think it would be better to make it propagate the result of
> >->address() rather than add a new callback, say, end_walk?
> >
> It's up to you. In my opinion, end_walk is better for reading.

I also prefer the way this patch works.

> >>
> >>Thank you.
> >>Byungchul
> >>
> >>>
> >>>>   	.walk_stack	= print_context_stack,
> >>>>+	.end_walk	= save_stack_end,
> >>>>   };
> >>>>
> >>>>   static const struct stacktrace_ops save_stack_ops_nosched = {
> >>>>
> >