Re: [PATCH 13/23] slub: create duplicate cache

[Frederic Weisbecker <fweisbec@gmail.com>]

On Sun, Apr 22, 2012 at 08:53:30PM -0300, Glauber Costa wrote:
> This patch provides kmem_cache_dup(), that duplicates
> a cache for a memcg, preserving its creation properties.
> Object size, alignment and flags are all respected.
> 
> When a duplicate cache is created, the parent cache cannot
> be destructed during the child lifetime. To assure this,
> its reference count is increased if the cache creation
> succeeds.
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> ---
>  include/linux/memcontrol.h |    3 +++
>  include/linux/slab.h       |    3 +++
>  mm/memcontrol.c            |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  mm/slub.c                  |   37 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 87 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 99e14b9..493ecdd 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -445,6 +445,9 @@ int memcg_css_id(struct mem_cgroup *memcg);
>  void mem_cgroup_register_cache(struct mem_cgroup *memcg,
>  				      struct kmem_cache *s);
>  void mem_cgroup_release_cache(struct kmem_cache *cachep);
> +extern char *mem_cgroup_cache_name(struct mem_cgroup *memcg,
> +				   struct kmem_cache *cachep);
> +
>  #else
>  static inline void mem_cgroup_register_cache(struct mem_cgroup *memcg,
>  					     struct kmem_cache *s)
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index c7a7e05..909b508 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -323,6 +323,9 @@ extern void *__kmalloc_track_caller(size_t, gfp_t, unsigned long);
>  
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>  #define MAX_KMEM_CACHE_TYPES 400
> +extern struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
> +					 struct kmem_cache *cachep);
> +void kmem_cache_drop_ref(struct kmem_cache *cachep);
>  #else
>  #define MAX_KMEM_CACHE_TYPES 0
>  #endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0015ed0..e881d83 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -467,6 +467,50 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
>  EXPORT_SYMBOL(tcp_proto_cgroup);
>  #endif /* CONFIG_INET */
>  
> +/*
> + * This is to prevent races againt the kmalloc cache creations.
> + * Should never be used outside the core memcg code. Therefore,
> + * copy it here, instead of letting it in lib/
> + */
> +static char *kasprintf_no_account(gfp_t gfp, const char *fmt, ...)
> +{
> +	unsigned int len;
> +	char *p = NULL;
> +	va_list ap, aq;
> +
> +	va_start(ap, fmt);
> +	va_copy(aq, ap);
> +	len = vsnprintf(NULL, 0, fmt, aq);
> +	va_end(aq);
> +
> +	p = kmalloc_no_account(len+1, gfp);

I can't seem to find kmalloc_no_account() in this patch or may be
I missed it in a previous one?

> +	if (!p)
> +		goto out;
> +
> +	vsnprintf(p, len+1, fmt, ap);
> +
> +out:
> +	va_end(ap);
> +	return p;
> +}
> +
> +char *mem_cgroup_cache_name(struct mem_cgroup *memcg, struct kmem_cache *cachep)
> +{
> +	char *name;
> +	struct dentry *dentry = memcg->css.cgroup->dentry;
> +
> +	BUG_ON(dentry == NULL);
> +
> +	/* Preallocate the space for "dead" at the end */
> +	name = kasprintf_no_account(GFP_KERNEL, "%s(%d:%s)dead",
> +	    cachep->name, css_id(&memcg->css), dentry->d_name.name);
> +
> +	if (name)
> +		/* Remove "dead" */
> +		name[strlen(name) - 4] = '\0';

Why this space for "dead" ? I can't seem to find a reference to that in
the kernel. Is it something I'm missing because of my lack of slab knowledge
or is it something needed in a further patch? In which case this should be
explained in the changelog.

> +	return name;
> +}
> +
>  /* Bitmap used for allocating the cache id numbers. */
>  static DECLARE_BITMAP(cache_types, MAX_KMEM_CACHE_TYPES);
>  
> diff --git a/mm/slub.c b/mm/slub.c
> index 86e40cc..2285a96 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3993,6 +3993,43 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
>  }
>  EXPORT_SYMBOL(kmem_cache_create);
>  
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> +struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
> +				  struct kmem_cache *s)
> +{
> +	char *name;
> +	struct kmem_cache *new;
> +
> +	name = mem_cgroup_cache_name(memcg, s);
> +	if (!name)
> +		return NULL;
> +
> +	new = kmem_cache_create_memcg(memcg, name, s->objsize, s->align,
> +				      s->allocflags, s->ctor);
> +
> +	/*
> +	 * We increase the reference counter in the parent cache, to
> +	 * prevent it from being deleted. If kmem_cache_destroy() is
> +	 * called for the root cache before we call it for a child cache,
> +	 * it will be queued for destruction when we finally drop the
> +	 * reference on the child cache.
> +	 */
> +	if (new) {
> +		down_write(&slub_lock);
> +		s->refcount++;
> +		up_write(&slub_lock);
> +	}
> +
> +	return new;
> +}
> +
> +void kmem_cache_drop_ref(struct kmem_cache *s)
> +{
> +	BUG_ON(s->memcg_params.id != -1);
> +	kmem_cache_destroy(s);
> +}
> +#endif
> +
>  #ifdef CONFIG_SMP
>  /*
>   * Use the cpu notifier to insure that the cpu slabs are flushed when
> -- 
> 1.7.7.6
> 
> --
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