linux-kernel - Re: [Bugme-new] [Bug 13690] New: nodes_clear cause hugepage unusable on non-NUMA machine

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Date:	Thu, 2 Jul 2009 10:11:30 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	alex.shi@...el.com, Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	"bugzilla-daemon@...zilla.kernel.org" 
	<bugzilla-daemon@...zilla.kernel.org>,
	"bugme-daemon@...zilla.kernel.org" <bugme-daemon@...zilla.kernel.org>,
	Mel Gorman <mel@....ul.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	yanmin.zhang@...el.com, tim.c.chen@...el.com
Subject: Re: [Bugme-new] [Bug 13690] New: nodes_clear cause hugepage unusable
 on non-NUMA machine

On Thu, 2 Jul 2009, Yinghai Lu wrote:

> Index: linux-2.6/arch/x86/mm/init_64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/init_64.c
> +++ linux-2.6/arch/x86/mm/init_64.c
> @@ -598,8 +598,14 @@ void __init paging_init(void)
>
>  	sparse_memory_present_with_active_regions(MAX_NUMNODES);
>  	sparse_init();
> -	/* clear the default setting with node 0 */
> +#if MAX_NUMNODES > 1
> +	/*
> +	 * clear the default setting with node 0
> +	 * note: don't clear it, node_set_state will do nothing
> +	 *	 (aka set it back) when numa support is not compiled in
> +	 */
>  	nodes_clear(node_states[N_NORMAL_MEMORY]);

The problem was that nodes_clear() does not fall back to a noop on !NUMA.
The node_set/clear_states() operations do become noops.

Could we make it more consistent by using only operations of the same
type? F.e. Add a node_clearall_states() in include/linux/nodemask.h that
falls back to a noop on !NUMA like the node_*_states operation?

Another options is to restore node_states[N_NORMAL_MEMORY] to its
initial condition. See the definition of node_states in page_alloc.c.
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