linux-kernel - Re: [2/2] vmallocinfo: Add caller information

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Message-ID: <Pine.LNX.4.64.0804291204450.12689@schroedinger.engr.sgi.com>
Date:	Tue, 29 Apr 2008 12:09:51 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [2/2] vmallocinfo: Add caller information

On Mon, 28 Apr 2008, Arjan van de Ven wrote:

> > Hmmm... Why do we have CONFIG_FRAMEPOINTER then?
> 
> to make the backtraces more accurate.

Well so we display out of whack backtraces? There are also issues on 
platforms that do not have a stack in the classic sense (rotating register 
file on IA64 and Sparc64 f.e.). Determining a backtrace can be very 
expensive.

> > The current implementation of vmalloc_caller() follows what we have
> > done with kmalloc_track_caller. Its low overhead and always on.
> 
> stacktraces aren't entirely free, the cost is O(nr of modules) unfortunately ;(

The current implementation /proc/vmallocinfo avoids these issues and 
with just one caller address it can print one line per vmalloc request. 
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