linux-kernel - Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

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Message-ID: <18107.61638.897455.3076@notabene.brown>
Date:	Fri, 10 Aug 2007 14:59:50 +1000
From:	Neil Brown <neilb@...e.de>
To:	"Dan Merillat" <dan.merillat@...il.com>
Cc:	"Eric Sandeen" <sandeen@...deen.net>,
	"Satyam Sharma" <satyam.sharma@...il.com>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Andrea Arcangeli" <andrea@...e.de>,
	"Matt Mackall" <mpm@...enic.com>,
	"Rene Herman" <rene.herman@...il.com>,
	"Ray Lee" <ray-lk@...rabbit.org>, "Bodo Eggert" <7eggert@....de>,
	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	"Jesper Juhl" <jesper.juhl@...il.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"William Lee Irwin III" <wli@...omorphy.com>,
	"David Chinner" <dgc@....com>,
	"Arjan van de Ven" <arjan@...radead.org>
Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

On Friday August 10, dan.merillat@...il.com wrote:
> On 8/1/07, Neil Brown <neilb@...e.de> wrote:
> 
> > No, this does not use indefinite stack.
> >
> > loop will schedule each request to be handled by a kernel thread, so
> > requests to 'loop' are serialised, never stacked.
> >
> > In 2.6.22, generic_make_request detects and serialises recursive calls,
> > so unlimited recursion is not possible there either.
> 
> Is that saying "before 2.6.22, a read/write on a deeply layered device
> would use a lot of stack?"

before 2.6.22, a stack of dm and/or md devices (not loop, and not
md/raid0 or md/linear) would use more stack the more devices were
involved.  If you made a very deep stack, you could push the stack
over any limit you chose.

I won't say "a lot of stack" as I haven't measured the exact amount,
just "more stack as you add more devices".

NeilBrown
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