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

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Date:	Sun, 20 Sep 2009 15:04:21 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Pekka Enberg <penberg@...helsinki.fi>
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 Sun, Sep 20, 2009 at 11:45:54AM +0300, Pekka Enberg wrote:
> 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?
> 

I don't think it should be merged as-is. This patch might be treating
symptons so needs further thought. The second patch is a hatchet job and
as Christoph points out, it may be suffering a subtle list-corruption
bug.

> > 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
> >
> > --
> > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > the body to majordomo@...ck.org.  For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
> > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> >
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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