Re: [PATCH v5 16/18] x86/sgx: Limit process EPC usage with misc cgroup controller

[Huang, Kai]

> +/**
> + * sgx_epc_cgroup_lru_empty() - check if a cgroup tree has no pages on its lrus
> + * @root:	root of the tree to check
> + *
> + * Return: %true if all cgroups under the specified root have empty LRU lists.
> + * Used to avoid livelocks due to a cgroup having a non-zero charge count but
> + * no pages on its LRUs, e.g. due to a dead enclave waiting to be released or
> + * because all pages in the cgroup are unreclaimable.
> + */
> +bool sgx_epc_cgroup_lru_empty(struct sgx_epc_cgroup *root)
> +{
> +	struct cgroup_subsys_state *css_root;
> +	struct cgroup_subsys_state *pos;
> +	struct sgx_epc_cgroup *epc_cg;
> +	bool ret = true;
> +
> +	/*
> +	 * Caller ensure css_root ref acquired
> +	 */
> +	css_root = root ? &root->cg->css : &(misc_cg_root()->css);
> +
> +	rcu_read_lock();
> +	css_for_each_descendant_pre(pos, css_root) {
> +		if (!css_tryget(pos))
> +			break;
> +
> +		rcu_read_unlock();
> +
> +		epc_cg = sgx_epc_cgroup_from_misc_cg(css_misc(pos));
> +
> +		spin_lock(&epc_cg->lru.lock);
> +		ret = list_empty(&epc_cg->lru.reclaimable);
> +		spin_unlock(&epc_cg->lru.lock);
> +
> +		rcu_read_lock();
> +		css_put(pos);
> +		if (!ret)
> +			break;
> +	}
> +
> +	rcu_read_unlock();
> +
> +	return ret;
> +}
> 

[...]

> 
>  static inline bool sgx_can_reclaim(void)
>  {
> +	if (IS_ENABLED(CONFIG_CGROUP_SGX_EPC))
> +		return !sgx_epc_cgroup_lru_empty(NULL);
> +

Is it better to keep a root sgx_epc_cgroup and pass the root instead of NULL?

>  	return !list_empty(&sgx_global_lru.reclaimable);
>  }
>