linux-kernel - Re: [PATCH v3] mm: make expand_downwards symmetrical to expand

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Date:	Wed, 20 Apr 2011 10:34:23 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	linux-parisc@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Ingo Molnar <mingo@...e.hu>, x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH v3] mm: make expand_downwards symmetrical to expand_upwards

Hi!

On Wed, Apr 20, 2011 at 4:23 AM, KOSAKI Motohiro
>> <kosaki.motohiro@...fujitsu.com> wrote:
>> > I'm worry about this patch. A lot of mm code assume !NUMA systems
>> > only have node 0. Not only SLUB.
>>
>> So is that a valid assumption or not? Christoph seems to think it is
>> and James seems to think it's not. Which way should we aim to fix it?
>> Would be nice if other people chimed in as we already know what James
>> and Christoph think.

On Wed, Apr 20, 2011 at 10:15 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
> I'm sorry. I don't know it really. The fact was gone into historical myst. ;-)
>
> Now, CONFIG_NUMA has mainly five meanings.
>
> 1) system may has !0 node id.
> 2) compile mm/mempolicy.c (ie enable mempolicy APIs)
> 3) Allocator (kmalloc, vmalloc, alloc_page, et al) awake NUMA topology.
> 4) enable zone-reclaim feature
> 5) scheduler makes per-node load balancing scheduler domain
>
> Anyway, we have to fix this issue.  I'm digging which fixing way has least risk.
>
>
> btw, x86 don't have an issue. Probably it's a reason why this issue was neglected
> long time.
>
> arch/x86/Kconfig
> -------------------------------------
> config ARCH_DISCONTIGMEM_ENABLE
>        def_bool y
>        depends on NUMA && X86_32

That part makes me think the best option is to make parisc do
CONFIG_NUMA as well regardless of the historical intent was.

                        Pekka
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