linux-kernel - Re: [PATCH v3 12/28] slab: pass memcg parameter to kmem_cache

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Date:	Tue, 29 May 2012 09:27:52 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, kamezawa.hiroyu@...fujitsu.com,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, devel@...nvz.org,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v3 12/28] slab: pass memcg parameter to
 kmem_cache_create

On Fri, 25 May 2012, Glauber Costa wrote:

> index 06e4a3e..7c0cdd6 100644
> --- a/include/linux/slab_def.h
> +++ b/include/linux/slab_def.h
> @@ -102,6 +102,13 @@ struct kmem_cache {
>  	 */
>  };
>
> +static inline void store_orig_align(struct kmem_cache *cachep, int orig_align)
> +{
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> +	cachep->memcg_params.orig_align = orig_align;
> +#endif
> +}
> +

Why do you need to store the original alignment? Is the calculated
alignment not enough?

> +++ b/mm/slab.c
> @@ -1729,6 +1729,31 @@ void __init kmem_cache_init_late(void)
>  	 */
>  }
>
> +static int __init memcg_slab_register_all(void)
> +{
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> +	struct kmem_cache *cachep;
> +	struct cache_sizes *sizes;
> +
> +	sizes = malloc_sizes;
> +
> +	while (sizes->cs_size != ULONG_MAX) {
> +		if (sizes->cs_cachep)
> +			mem_cgroup_register_cache(NULL, sizes->cs_cachep);
> +		if (sizes->cs_dmacachep)
> +			mem_cgroup_register_cache(NULL, sizes->cs_dmacachep);
> +		sizes++;
> +	}
> +
> +	mutex_lock(&cache_chain_mutex);
> +	list_for_each_entry(cachep, &cache_chain, next)
> +		mem_cgroup_register_cache(NULL, cachep);
> +
> +	mutex_unlock(&cache_chain_mutex);
> +#endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
> +	return 0;
> +}

Ok this only duplicates the kmalloc arrays. Why not the others?

> @@ -2331,7 +2350,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>  			continue;
>  		}
>
> -		if (!strcmp(pc->name, name)) {
> +		if (!memcg && !strcmp(pc->name, name)) {
>  			printk(KERN_ERR
>  			       "kmem_cache_create: duplicate cache %s\n", name);
>  			dump_stack();

This implementation means that duplicate cache detection will no longer
work within a cgroup?

> @@ -2543,7 +2564,12 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>  	cachep->ctor = ctor;
>  	cachep->name = name;
>
> +	if (g_cpucache_up >= FULL)
> +		mem_cgroup_register_cache(memcg, cachep);

What happens if a cgroup was active during creation of slab xxy but
then a process running in a different cgroup uses that slab to allocate
memory? Is it charged to the first cgroup?
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