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From: Neil Brown <neilb@suse.de>
To: "Dan Merillat" <dan.merillat@gmail.com>
Date: Fri, 10 Aug 2007 14:59:50 +1000
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Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?
In-Reply-To: message from Dan Merillat on Friday August 10
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On Friday August 10, dan.merillat@gmail.com wrote:
> On 8/1/07, Neil Brown <neilb@suse.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