netdev - Re: [PATCH v2 net-next 4/6] bpf: Add BPF_MAP_TYPE_LRU

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Message-ID: <20161114205222.GA1655@ast-mbp.thefacebook.com>
Date:   Mon, 14 Nov 2016 12:52:23 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 net-next 4/6] bpf: Add BPF_MAP_TYPE_LRU_HASH

On Fri, Nov 11, 2016 at 10:55:09AM -0800, Martin KaFai Lau wrote:
> Provide a LRU version of the existing BPF_MAP_TYPE_HASH.
> 
> Signed-off-by: Martin KaFai Lau <kafai@...com>
...
> +/* Instead of having one common LRU list in the
> + * BPF_MAP_TYPE_LRU_HASH map, use a percpu LRU list
> + * which can scale and perform better.
> + * Note, the LRU nodes (including free nodes) cannot be moved
> + * across different LRU lists.
> + */
> +#define BPF_F_NO_COMMON_LRU	(1U << 1)

I couldn't come up with better name, so I think it's good :)

> +	if (lru && !capable(CAP_SYS_ADMIN))
> +		/* LRU implementation is much complicated than other
> +		 * maps.  Hence, limit to CAP_SYS_ADMIN for now.
> +		 */
> +		return ERR_PTR(-EPERM);

+1
good call.

> +	if (!percpu && !lru) {
> +		/* lru itself can remove the least used element, so
> +		 * there is no need for an extra elem during map_update.
> +		 */

yeah. that's an important comment, otherwise
@@ -48,11 +52,19 @@ struct htab_elem {
 	union {
 		struct rcu_head rcu;
 		enum extra_elem_state state;
+		struct bpf_lru_node lru_node;
 	};
wouldn't be correct.

Acked-by: Alexei Starovoitov <ast@...nel.org>