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Date: Thu, 19 Jul 2007 13:24:36 +0200
From: Andrea Arcangeli <andrea@suse.de>
To: Matt Mackall <mpm@selenic.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Rene Herman <rene.herman@gmail.com>,
       Ray Lee <ray-lk@madrabbit.org>, Bodo Eggert <7eggert@gmx.de>,
       Jeremy Fitzhardinge <jeremy@goop.org>,
       Jesper Juhl <jesper.juhl@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       William Lee Irwin III <wli@holomorphy.com>, David Chinner <dgc@sgi.com>,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?
Message-ID: <20070719112436.GG29728@v2.random>
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On Wed, Jul 18, 2007 at 08:37:25PM -0500, Matt Mackall wrote:
> Turn on irqstacks when using 8k stacks

Indeed.

> Detect when usage with 8k stacks would overrun a 4k stack when doing
>  our stack switch and do a WARN_ONCE
> Fix up the damn bugs

I don't think they're necessarily bugs. IMHO the WARN_ON is better off
at 7k level like it is today with the current STACK_WARN. 4k for a
stack for common code really is small. I doubt you're going to find
obvious culprits that way, more likely you'll have to mangle the code
to call kmalloc for fairly small structures which isn't necessarily a
good thing in the long term. It comes to mind the folio ptes array
that Hugh allocated on the stack in his large PAGE_SIZE patch of jul
2001, that thing like any other local array, would need to be
kmalloced with a 4k stack. With 4k I'm afraid you better not use the
stack for anything but pointers, especially if you run in common code
that may invoke I/O like that.