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

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Date:	Thu, 04 Oct 2007 14:08:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <ak@...e.de>
Cc:	Christoph Lameter <clameter@....com>, 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 Thu, 2007-10-04 at 13:56 +0200, Andi Kleen wrote:
> On Thursday 04 October 2007 05:59:48 Christoph Lameter wrote:
> > Peter Zijlstra has recently demonstrated that we can have order 1 allocation
> > failures under memory pressure with small memory configurations. The
> > x86_64 stack has a size of 8k and thus requires a order 1 allocation.
> 
> We've known for ages that it is possible. But it has been always so rare
> that it was ignored.
> 
> Is there any evidence this is more common now than it used to be?

The order-1 allocation failures where GFP_ATOMIC, because SLUB uses !0
order for everything. Kernel stack allocation is GFP_KERNEL I presume.
Also, I use 4k stacks on all my machines.

Maybe the cpumask thing needs an extended api, one that falls back to
kmalloc if NR_CPUS >> sane.

That way that cannot be an argument to inflate stacks.

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