Date: Fri, 27 Feb 2015 15:30:08 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andi Kleen <ak@linux.intel.com>, Andi Kleen <andi@firstfloor.org>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        mathieu.desnoyers@efficios.com, oleg@redhat.com,
        paulmck@linux.vnet.ibm.com, mingo@kernel.org
Subject: Re: [RFC][PATCH] module: Optimize __module_address() using a latched
 RB-tree
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On Fri, Feb 27, 2015 at 10:32:39PM +1030, Rusty Russell wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
> > One of the users of this is __kernel_text_address() which is employed in
> > many stack unwinders; which in turn are used by perf-callchain (possibly
> > from NMI context).
> 
> Um, so the stack unwinders use "does this look like a kernel address"
> because we omit the frame pointer?

Not only because of that I think; also as a general robustness check.
I'm not sure people want their stack unwinder to go off into the woods.

> To keep that optimization, we add 220 non-trivial lines to module.c?

Can I make you feel better by writing more comments? I'm not sure we can
convince the arch people to take this test out. Its all over the place.

> Don't get me wrong, it's cute code, but I do wonder if at some point a
> grown up is going to come along and tell us to stop :)

Now where's the fun in that ;-)
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