linux-kernel - Re: [13/18] x86_64: Allow fallback for the stack

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Date:	Tue, 9 Oct 2007 18:46:22 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <clameter@....com>
Cc:	Rik van Riel <riel@...hat.com>, Andi Kleen <ak@...e.de>,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, travis@....com
Subject: Re: [13/18] x86_64: Allow fallback for the stack

On Wednesday 10 October 2007 04:39, Christoph Lameter wrote:
> On Mon, 8 Oct 2007, Nick Piggin wrote:
> > The tight memory restrictions on stack usage do not come about because
> > of the difficulty in increasing the stack size :) It is because we want
> > to keep stack sizes small!
> >
> > Increasing the stack size 4K uses another 4MB of memory for every 1000
> > threads you have, right?
> >
> > It would take a lot of good reason to move away from the general
> > direction we've been taking over the past years that 4/8K stacks are a
> > good idea for regular 32 and 64 bit builds in general.
>
> We already use 32k stacks on IA64. So the memory argument fail there.

I'm talking about generic code.


> > > I have some concerns about the medium NUMA systems (a few dozen of
> > > nodes) also running out of stack since more data is placed on the stack
> > > through the policy layer and since we may end up with a couple of
> > > stacked filesystems. Most of the current NUMA systems on x86_64 are
> > > basically two nodes on one motherboard. The use of NUMA controls is
> > > likely limited there and the complexity of the filesystems is also not
> > > high.
> >
> > The solution has until now always been to fix the problems so they don't
> > use so much stack. Maybe a bigger stack is OK for you for 1024+ CPU
> > systems, but I don't think you'd be able to make that assumption for most
> > normal systems.
>
> Yes that is why I made the stack size configurable.

Fine. I just don't see why you need this fallback.
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