linux-kernel - Re: [PATCH 1/3] slqb: Do not use DEFINE_PER

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Date:	Sun, 20 Sep 2009 11:45:54 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Nick Piggin <npiggin@...e.de>,
	Christoph Lameter <cl@...ux-foundation.org>,
	heiko.carstens@...ibm.com, sachinp@...ibm.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] slqb: Do not use DEFINE_PER_CPU for per-node data

On Fri, Sep 18, 2009 at 10:34 PM, Mel Gorman <mel@....ul.ie> wrote:
> SLQB used a seemingly nice hack to allocate per-node data for the statically
> initialised caches. Unfortunately, due to some unknown per-cpu
> optimisation, these regions are being reused by something else as the
> per-node data is getting randomly scrambled. This patch fixes the
> problem but it's not fully understood *why* it fixes the problem at the
> moment.

Ouch, that sounds bad. I guess it's architecture specific bug as x86
works ok? Lets CC Tejun.

Nick, are you okay with this patch being merged for now?

> Signed-off-by: Mel Gorman <mel@....ul.ie>
> ---
>  mm/slqb.c |   16 ++++++++--------
>  1 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/mm/slqb.c b/mm/slqb.c
> index 4ca85e2..4d72be2 100644
> --- a/mm/slqb.c
> +++ b/mm/slqb.c
> @@ -1944,16 +1944,16 @@ static void init_kmem_cache_node(struct kmem_cache *s,
>  static DEFINE_PER_CPU(struct kmem_cache_cpu, kmem_cache_cpus);
>  #endif
>  #ifdef CONFIG_NUMA
> -/* XXX: really need a DEFINE_PER_NODE for per-node data, but this is better than
> - * a static array */
> -static DEFINE_PER_CPU(struct kmem_cache_node, kmem_cache_nodes);
> +/* XXX: really need a DEFINE_PER_NODE for per-node data because a static
> + *      array is wasteful */
> +static struct kmem_cache_node kmem_cache_nodes[MAX_NUMNODES];
>  #endif
>
>  #ifdef CONFIG_SMP
>  static struct kmem_cache kmem_cpu_cache;
>  static DEFINE_PER_CPU(struct kmem_cache_cpu, kmem_cpu_cpus);
>  #ifdef CONFIG_NUMA
> -static DEFINE_PER_CPU(struct kmem_cache_node, kmem_cpu_nodes); /* XXX per-nid */
> +static struct kmem_cache_node kmem_cpu_nodes[MAX_NUMNODES]; /* XXX per-nid */
>  #endif
>  #endif
>
> @@ -1962,7 +1962,7 @@ static struct kmem_cache kmem_node_cache;
>  #ifdef CONFIG_SMP
>  static DEFINE_PER_CPU(struct kmem_cache_cpu, kmem_node_cpus);
>  #endif
> -static DEFINE_PER_CPU(struct kmem_cache_node, kmem_node_nodes); /*XXX per-nid */
> +static struct kmem_cache_node kmem_node_nodes[MAX_NUMNODES]; /*XXX per-nid */
>  #endif
>
>  #ifdef CONFIG_SMP
> @@ -2918,15 +2918,15 @@ void __init kmem_cache_init(void)
>        for_each_node_state(i, N_NORMAL_MEMORY) {
>                struct kmem_cache_node *n;
>
> -               n = &per_cpu(kmem_cache_nodes, i);
> +               n = &kmem_cache_nodes[i];
>                init_kmem_cache_node(&kmem_cache_cache, n);
>                kmem_cache_cache.node_slab[i] = n;
>  #ifdef CONFIG_SMP
> -               n = &per_cpu(kmem_cpu_nodes, i);
> +               n = &kmem_cpu_nodes[i];
>                init_kmem_cache_node(&kmem_cpu_cache, n);
>                kmem_cpu_cache.node_slab[i] = n;
>  #endif
> -               n = &per_cpu(kmem_node_nodes, i);
> +               n = &kmem_node_nodes[i];
>                init_kmem_cache_node(&kmem_node_cache, n);
>                kmem_node_cache.node_slab[i] = n;
>        }
> --
> 1.6.3.3
>
> --
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