linux-kernel - Re: Large stack usage in fs code (especially for PPC64)

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Message-ID: <20081118103726.GB31146@elte.hu>
Date:	Tue, 18 Nov 2008 11:37:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>, linuxppc-dev@...abs.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: Large stack usage in fs code (especially for PPC64)


* Christoph Hellwig <hch@...radead.org> wrote:

> On Tue, Nov 18, 2008 at 10:03:25AM +1100, Benjamin Herrenschmidt wrote:
> > On Mon, 2008-11-17 at 15:34 -0500, Steven Rostedt wrote:
> > > Note, I was using a default config that had CONFIG_IRQSTACKS off and
> > > CONFIG_PPC_64K_PAGES on.
> > 
> > For one, we definitely need to turn IRQSTACKS on by default ... In fact,
> > I'm pondering just removing the option.
> 
> It shouldn't be a user-visible option.  It shouldn't on x86 either, 
> but there it always gets into the ideological 4k stacks flameware so 
> people usually gave up after a while instead of doing the sensibke 
> 8k + irqstacks by default, 4k as an option..

yep, i tend to agree that 8k + irqstacks on both 32-bit and 64-bit 
would be the sane default. There's just too much gcc and other noise 
for us to have that cushion by default on 32-bit too. 64-bit is 
already there, on 32-bit we should decouple irqstacks from 4K stacks 
and just turn irqstacks on by default.

Life's too short to fight kernel stack overflows - and now we've got 
the stack-tracer that will record and show the frame of the worst-ever 
kernel stack situation the system was in since bootup. (see Steve's 
tracer output in this thread)

	Ingo
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