linux-kernel - Re: [PATCH] Fix boot problem in situations where the boot CPU is running on a memoryless node

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Message-ID: <Pine.LNX.4.64.0801231611160.20050@sbz-30.cs.Helsinki.FI>
Date:	Wed, 23 Jan 2008 16:18:19 +0200 (EET)
From:	Pekka J Enberg <penberg@...helsinki.fi>
To:	Mel Gorman <mel@....ul.ie>
cc:	akpm@...ux-foundation.org, Christoph Lameter <clameter@....com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	hanth Aravamudan <nacc@...ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	lee.schermerhorn@...com, Linux MM <linux-mm@...ck.org>,
	Olaf Hering <olaf@...fle.de>
Subject: Re: [PATCH] Fix boot problem in situations where the boot CPU is
 running on a memoryless node

Hi Mel,

On Wed, 23 Jan 2008, Mel Gorman wrote:
> diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.24-rc8-005-revert-memoryless-slab/mm/slab.c linux-2.6.24-rc8-010_handle_missing_l3/mm/slab.c
> --- linux-2.6.24-rc8-005-revert-memoryless-slab/mm/slab.c	2008-01-22 17:46:32.000000000 +0000
> +++ linux-2.6.24-rc8-010_handle_missing_l3/mm/slab.c	2008-01-22 18:42:53.000000000 +0000
> @@ -2775,6 +2775,11 @@ static int cache_grow(struct kmem_cache 
>  	/* Take the l3 list lock to change the colour_next on this node */
>  	check_irq_off();
>  	l3 = cachep->nodelists[nodeid];
> +	if (!l3) {
> +		nodeid = numa_node_id();
> +		l3 = cachep->nodelists[nodeid];
> +	}
> +	BUG_ON(!l3);
>  	spin_lock(&l3->list_lock);
>  
>  	/* Get colour for the slab, and cal the next value. */
> @@ -3317,6 +3322,10 @@ static void *____cache_alloc_node(struct
>  	int x;
>  
>  	l3 = cachep->nodelists[nodeid];
> +	if (!l3) {
> +		nodeid = numa_node_id();
> +		l3 = cachep->nodelists[nodeid];
> +	}

What guarantees that current node ->nodelists is never NULL?

I still think Christoph's kmem_getpages() patch is correct (to fix 
cache_grow() oops) but I overlooked the fact that none the callers of 
____cache_alloc_node() deal with bootstrapping (with the exception of 
__cache_alloc_node() that even has a comment about it).

But what I am really wondering about is, why wasn't the 
N_NORMAL_MEMORY revert enough? I assume this used to work before so what 
more do we need to revert for 2.6.24?

			Pekka
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