[Devel] Re: [PATCH 17/23] kmem controller charge/uncharge infrastructure

[David Rientjes]

On Sun, 22 Apr 2012, Glauber Costa wrote:

> +/*
> + * Return the kmem_cache we're supposed to use for a slab allocation.
> + * If we are in interrupt context or otherwise have an allocation that
> + * can't fail, we return the original cache.
> + * Otherwise, we will try to use the current memcg's version of the cache.
> + *
> + * If the cache does not exist yet, if we are the first user of it,
> + * we either create it immediately, if possible, or create it asynchronously
> + * in a workqueue.
> + * In the latter case, we will let the current allocation go through with
> + * the original cache.
> + *
> + * This function returns with rcu_read_lock() held.
> + */
> +struct kmem_cache *__mem_cgroup_get_kmem_cache(struct kmem_cache *cachep,
> +					     gfp_t gfp)
> +{
> +	struct mem_cgroup *memcg;
> +	int idx;
> +
> +	gfp |=  cachep->allocflags;
> +
> +	if ((current->mm == NULL))
> +		return cachep;
> +
> +	if (cachep->memcg_params.memcg)
> +		return cachep;
> +
> +	idx = cachep->memcg_params.id;
> +	VM_BUG_ON(idx == -1);
> +
> +	memcg = mem_cgroup_from_task(current);
> +	if (!mem_cgroup_kmem_enabled(memcg))
> +		return cachep;
> +
> +	if (rcu_access_pointer(memcg->slabs[idx]) == NULL) {
> +		memcg_create_cache_enqueue(memcg, cachep);
> +		return cachep;
> +	}
> +
> +	return rcu_dereference(memcg->slabs[idx]);
> +}
> +EXPORT_SYMBOL(__mem_cgroup_get_kmem_cache);
> +
> +void mem_cgroup_remove_child_kmem_cache(struct kmem_cache *cachep, int id)
> +{
> +	rcu_assign_pointer(cachep->memcg_params.memcg->slabs[id], NULL);
> +}
> +
> +bool __mem_cgroup_charge_kmem(gfp_t gfp, size_t size)
> +{
> +	struct mem_cgroup *memcg;
> +	bool ret = true;
> +
> +	rcu_read_lock();
> +	memcg = mem_cgroup_from_task(current);

This seems horribly inconsistent with memcg charging of user memory since 
it charges to p->mm->owner and you're charging to p.  So a thread attached 
to a memcg can charge user memory to one memcg while charging slab to 
another memcg?

> +
> +	if (!mem_cgroup_kmem_enabled(memcg))
> +		goto out;
> +
> +	mem_cgroup_get(memcg);
> +	ret = memcg_charge_kmem(memcg, gfp, size) == 0;
> +	if (ret)
> +		mem_cgroup_put(memcg);
> +out:
> +	rcu_read_unlock();
> +	return ret;
> +}
> +EXPORT_SYMBOL(__mem_cgroup_charge_kmem);
> +
> +void __mem_cgroup_uncharge_kmem(size_t size)
> +{
> +	struct mem_cgroup *memcg;
> +
> +	rcu_read_lock();
> +	memcg = mem_cgroup_from_task(current);
> +
> +	if (!mem_cgroup_kmem_enabled(memcg))
> +		goto out;
> +
> +	mem_cgroup_put(memcg);
> +	memcg_uncharge_kmem(memcg, size);
> +out:
> +	rcu_read_unlock();
> +}
> +EXPORT_SYMBOL(__mem_cgroup_uncharge_kmem);