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

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Message-ID: <Pine.LNX.4.64.0710091138250.32162@schroedinger.engr.sgi.com>
Date:	Tue, 9 Oct 2007 11:39:21 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
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 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 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.

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