netdev - Re: [PATCH net-next] bpf: Optimize lpm trie delete

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Date:   Wed, 20 Sep 2017 18:51:53 +0200
From:   Daniel Mack <daniel@...que.org>
To:     Craig Gallek <kraigatgoog@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next] bpf: Optimize lpm trie delete

Hi Craig,

Thanks, this looks much cleaner already :)

On 09/20/2017 06:22 PM, Craig Gallek wrote:
> diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
> index 9d58a576b2ae..b5a7d70ec8b5 100644
> --- a/kernel/bpf/lpm_trie.c
> +++ b/kernel/bpf/lpm_trie.c
> @@ -397,7 +397,7 @@ static int trie_delete_elem(struct bpf_map *map, void *_key)
>  	struct lpm_trie_node __rcu **trim;
>  	struct lpm_trie_node *node;
>  	unsigned long irq_flags;
> -	unsigned int next_bit;
> +	unsigned int next_bit = 0;

This default assignment seems wrong, and I guess you only added it to
squelch a compiler warning?

[...]

> +	/* If the node has one child, we may be able to collapse the tree
> +	 * while removing this node if the node's child is in the same
> +	 * 'next bit' slot as this node was in its parent or if the node
> +	 * itself is the root.
> +	 */
> +	if (trim == &trie->root) {
> +		next_bit = node->child[0] ? 0 : 1;
> +		rcu_assign_pointer(trie->root, node->child[next_bit]);
> +		kfree_rcu(node, rcu);

I don't think you should treat this 'root' case special.

Instead, move the 'next_bit' assignment outside of the condition ...

> +	} else if (rcu_access_pointer(node->child[next_bit])) {
> +		rcu_assign_pointer(*trim, node->child[next_bit]);
> +		kfree_rcu(node, rcu);

... and then this branch would handle the case just fine. Correct?

Otherwise, looks good to me!



Thanks,
Daniel