linux-kernel - Re: [PATCH 0/3] x86: Reduce memory usage for large count NR

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Date:	Tue, 22 Jan 2008 13:48:11 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	travis@....com
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Andi Kleen <ak@...e.de>,
	Christoph Lameter <clameter@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] x86: Reduce memory usage for large count NR_CPUs
	fixup V2 with git-x86

* travis@....com <travis@....com> wrote:

> Fixup change NR_CPUS patchset by rebasing on 2.6.24-rc8-mm1
> from 2.6.24-rc6-mm1) and adding changes suggested by reviews.
> 
> Based on 2.6.24-rc8-mm1 + latest (08/1/21) git-x86
> 
> Note there are two versions of this patchset:
> 	- 2.6.24-rc8-mm1
> 	- 2.6.24-rc8-mm1 + latest (08/1/21) git-x86

thanks, applied.

> Signed-off-by: Mike Travis <travis@....com>
> ---
> Fixup-V2:
>     - pulled the SMP_MAX patch as it's not strictly needed and some
>       more work on local cpumask_t variables needs to be done before
>       NR_CPUS is allowed to increase.

i'd still love to see CONFIG_SMP_MAX, so that we can have continuous 
randconfig testing of the large-SMP aspects of the x86 architecture, 
even on smaller systems.

What's the maximum that should work right now? 256 or perhaps even 512 
CPU ought to work fine i think?

and then once the on-stack usage problems are fixed, the NR_CPUS value 
in CONFIG_SMP_MAX can be increased. So SMP_MAX would also act as "this 
is how far we can go in the upstream kernel" documentation.

[ btw., the crash i remember was rather related to the NODES_SHIFT
  increase to 9, not from the NR_CPUSs increase. (the config i sent 
  still has NR_CPUS==8, because Kconfig did not pick up the right 
  NR_CPUs value dicatated by SMP_MAX.) If you resend the SMP_MAX patch 
  against latest x86.git i can retest this. ]

	Ingo
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