Date:	Mon, 21 Apr 2008 22:05:38 +0200 (CEST)
From:	Bodo Eggert <7eggert@....de>
To:	Daniel Hazelton <dhazelton@...er.net>
cc:	7eggert@....de, Adrian Bunk <bunk@...nel.org>,
	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>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: x86: 4kstacks default

On Sun, 20 Apr 2008, Daniel Hazelton wrote:
> On Sunday 20 April 2008 16:23:45 Bodo Eggert wrote:
> > Daniel Hazelton <dhazelton@...er.net> wrote:
> > > On Sunday 20 April 2008 08:27:14 Andi Kleen wrote:
> > >> Adrian Bunk <bunk@...nel.org> writes:

> > >> > 6k is known to work, and there aren't many problems known with 4k.
> > >> >
> > >> > And from a QA point of view the only way of getting 4k thoroughly
> > >> > tested
> > >>
> > >> But you have to first ask why do you want 4k tested? Does it serve
> > >> any useful purpose in itself? I don't think so. Or you're saying
> > >> it's important to support 50k kernel threads on 32bit kernels?
> > >
> > > Andi, you're the only one I've seen seriously pounding the "50k threads"
> > > thing - I don't think anyone is really fooled by the straw-man, so I'd
> > > suggest you drop it.
> > >
> > > The real issue is that you think (and are correct in thinking) that
> > > people are idiots. Yes, there will be breakages if the default is changed
> > > to 4k stacks - but if people are running new kernels on boxes that'll hit
> > > stack use problems (that *AREN'T* related to ndiswrapper) and haven't
> > > made sure that they've configured the kernel properly, then they deserve
> > > the outcome. It isn't the job of the Linux Kernel to protect the
> > > incompetent - nor is it the job of linux kernel developers to do such.
> >
> > It's the job of the kernel developers to mark experimental and broken
> > options, and to put a warning:
> >
> > "This will break stacking of drivers, especially if disk manager, xfs, RAID
> > and nfs are used. Yes, linux is broken by default, but only if you intend
> > to set up a reliable system, so this will be OK!"
> >
> > into the help text, instead of expecting each admin to read lkml.
> 
> Note that I've yet to meet a competent admin that creates brand new 
> configurations each time they build a new kernel for a machine.

Once is enough, and if you build a costom kernel, you'll certainly not 
want to start from the distribution's allmodconfig.

> Usually they 
> have a "default configuration" for each machine that gets updated each time a 
> new kernel is built. Usually they don't change working options. And since 
> changing things to 4K stacks default would cause a new option - the "8K 
> stacks" option to show up in a "make oldconfig" run - the admin would see it 
> and, hopefully, check the help text and see that it his system, with a deeply 
> stacked driver system (nfs+xfs+raid, for example) and set the 8K stacks 
> option to "Y".

The help text does not yet say anything about crashing.

> As I said, it isn't the job of the kernel or kernel developers to protect the 
> incompetent (or the lazy).

It's only incompetent if it's reasonable to expect a crashing kernel to
result from chosing the default values.
-- 
bus error. passengers dumped.
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