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

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Date:	Tue, 22 Jan 2008 07:10:06 -0800
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
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

Ingo Molnar wrote:
> * 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?

I'm attempting to gather stack (and memory) usage for increased cpu counts
right now.  But I'll have another set of basic changes before the cpumask_t
changes can be done.

Thanks,
Mike

> 
> 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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