On Mon, 3 Feb 2014 19:54:37 +0400 Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> wrote:
> The way memcg_create_kmem_cache() creates the name for a memcg cache
> looks rather strange: it first formats the name in the static buffer
> tmp_name protected by a mutex, then passes the pointer to the buffer to
> kmem_cache_create_memcg(), which finally duplicates it to the cache
> name.
>
> Let's clean this up by moving memcg cache name creation to a separate
> function to be called by kmem_cache_create_memcg(), and estimating the
> length of the name string before copying anything to it so that we won't
> need a temporary buffer.
>
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3193,6 +3193,37 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
> return 0;
> }
>
> +static int memcg_print_cache_name(char *buf, size_t size,
> + struct mem_cgroup *memcg, struct kmem_cache *root_cache)
> +{
> + int ret;
> +
> + rcu_read_lock();
> + ret = snprintf(buf, size, "%s(%d:%s)", root_cache->name,
> + memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup));
> + rcu_read_unlock();
> + return ret;
> +}
> +
> +char *memcg_create_cache_name(struct mem_cgroup *memcg,
> + struct kmem_cache *root_cache)
> +{
> + int len;
> + char *name;
> +
> + /*
> + * We cannot use kasprintf() here, because cgroup_name() must be called
> + * under RCU protection.
> + */
> + len = memcg_print_cache_name(NULL, 0, memcg, root_cache);
> +
> + name = kmalloc(len + 1, GFP_KERNEL);
> + if (name)
> + memcg_print_cache_name(name, len + 1, memcg, root_cache);
but but but this assumes that cgroup_name(memcg->css.cgroup) did not
change between the two calls to memcg_print_cache_name(). If that is
the case then the locking was unneeded anyway.
> + return name;
> +}
> +
> int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s,
> struct kmem_cache *root_cache)
> {
> @@ -3397,44 +3428,6 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
> schedule_work(&cachep->memcg_params->destroy);
> }
>
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