linux-kernel - Re: x86: 4kstacks default

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Date:	Mon, 21 Apr 2008 09:30:01 +0600
From:	"Alexander E. Patrakov" <patrakov@...il.com>
To:	Adrian Bunk <bunk@...nel.org>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Eric Sandeen <sandeen@...deen.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Shawn Bohrer <shawn.bohrer@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: x86: 4kstacks default

Adrian Bunk wrote:
> On Sun, Apr 20, 2008 at 08:41:27AM -0700, Arjan van de Ven wrote:
>> ...
>> yes. Adrian is waay off in the weeds on this one. Nobody but him is suggesting to remove
>> 8Kb stacks. I think everyone else agrees that having both options is valuable; and there
>> are better ways to find+fix stack bloat than removing this config option.
> 
> I'm not arguing for removing the option immediately, but long-term we 
> shouldn't need it.
> 
> This comes from my experience of removing obsolete drivers for hardware 
> for which also a more recent driver exists:
> As long as there is some workaround (e.g. using an older driver or
> 8k stacks) the workaround will be used instead of the getting proper 
> bug reports and fixes.
> 
> As far as I know all problems that are known with 4k stacks are some 
> nested things with XFS in the trace.

This "as far as I know" is a problem itself. Is it possible to implement (e.g., 
using some form of memory protection in hardware, but I am not an expert here) 
an option with 8k stacks that, however, spams the log if the actual usage goes 
above 4k, and have this as a default for some time? If 4k stacks are the goal 
that is almost achieved, then this debugging option should have zero impact on 
performance.

-- 
Alexander E. Patrakov
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