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

Peter Zijlstra
2007-10-04T12:08:28Z

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.