Re: [PATCH v3] mm: SLAB Out-of-memory diagnostics

[Eric Dumazet]

On Fri, 2012-03-09 at 17:27 -0300, Rafael Aquini wrote:
> Following the example at mm/slub.c, add out-of-memory diagnostics to the
> SLAB allocator to help on debugging certain OOM conditions.
> 
> An example print out looks like this:
> 
>   <snip page allocator out-of-memory message>
>   SLAB: Unable to allocate memory on node 0 (gfp=0x11200)
>     cache: bio-0, object size: 192, order: 0
>     node 0: slabs: 3/3, objs: 60/60, free: 0

Should probably be :

   node: 0 slabs: 3/3, objs: 60/60, free: 0


> 
> Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
> ---
> v2:
> * drop the sysctl knob to override __GFP_NOWARN allocation flag (Pekka, David)
> 
> v3:
> * adjust the print output to match slub's warning printout (WANG Cong)
> 
>  mm/slab.c |   51 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 50 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index f0bd785..cda1ff6 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1731,6 +1731,52 @@ static int __init cpucache_init(void)
>  }
>  __initcall(cpucache_init);
>  
> +static noinline void
> +slab_out_of_memory(struct kmem_cache *cachep, gfp_t gfpflags, int nodeid)
> +{
> +	struct kmem_list3 *l3;
> +	struct slab *slabp;
> +	unsigned long flags;
> +	int node;
> +
> +	printk(KERN_WARNING
> +		"SLAB: Unable to allocate memory on node %d (gfp=0x%x)\n",
> +		nodeid, gfpflags);
> +	printk(KERN_WARNING "  cache: %s, object size: %d, order: %d\n",
> +		cachep->name, cachep->buffer_size, cachep->gfporder);
> +
> +	for_each_online_node(node) {
> +		unsigned long active_objs = 0, num_objs = 0, free_objects = 0;
> +		unsigned long active_slabs = 0, num_slabs = 0;
> +
> +		l3 = cachep->nodelists[node];
> +		if (!l3)
> +			continue;
> +
> +		spin_lock_irqsave(&l3->list_lock, flags);
> +		list_for_each_entry(slabp, &l3->slabs_full, list) {
> +			active_objs += cachep->num;
> +			active_slabs++;
> +		}
> +		list_for_each_entry(slabp, &l3->slabs_partial, list) {
> +			active_objs += slabp->inuse;
> +			active_slabs++;
> +		}
> +		list_for_each_entry(slabp, &l3->slabs_free, list)
> +			num_slabs++;
> +
> +		free_objects += l3->free_objects;
> +		spin_unlock_irqrestore(&l3->list_lock, flags);
> +
> +		num_slabs += active_slabs;
> +		num_objs = num_slabs * cachep->num;
> +		printk(KERN_WARNING
> +			"  node %d: slabs: %ld/%ld, objs: %ld/%ld, free: %ld\n",

Probably should be :
		"  node: %d slabs: %ld/%ld, objs: %ld/%ld, free: %ld\n",

> +			node, active_slabs, num_slabs, active_objs, num_objs,
> +			free_objects);
> +	}
> +}
> +
>  /*
>   * Interface to system's page allocator. No need to hold the cache-lock.
>   *
> @@ -1757,8 +1803,11 @@ static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid)
>  		flags |= __GFP_RECLAIMABLE;
>  
>  	page = alloc_pages_exact_node(nodeid, flags | __GFP_NOTRACK, cachep->gfporder);
> -	if (!page)
> +	if (!page) {
> +		if (!(flags & __GFP_NOWARN) && printk_ratelimit())
> +			slab_out_of_memory(cachep, flags, nodeid);
>  		return NULL;
> +	}
>  
>  	nr_pages = (1 << cachep->gfporder);
>  	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)


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