Date: Tue, 9 Oct 2007 11:39:21 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
cc: Rik van Riel <riel@redhat.com>, Andi Kleen <ak@suse.de>,
       akpm@linux-foundation.org, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, travis@sgi.com
Subject: Re: [13/18] x86_64: Allow fallback for the stack
In-Reply-To: <200710082255.05598.nickpiggin@yahoo.com.au>
Message-ID: <Pine.LNX.4.64.0710091138250.32162@schroedinger.engr.sgi.com>
References: <20071004035935.042951211@sgi.com> <200710071735.41386.nickpiggin@yahoo.com.au>
 <Pine.LNX.4.64.0710081032030.26382@schroedinger.engr.sgi.com>
 <200710082255.05598.nickpiggin@yahoo.com.au>
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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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