netdev - Re: [PATCH v2 net-next 5/6] bpf: Add BPF_MAP_TYPE_LRU_PERCPU

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Date:   Mon, 14 Nov 2016 17:34:38 -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 5/6] bpf: Add BPF_MAP_TYPE_LRU_PERCPU_HASH

On Fri, Nov 11, 2016 at 10:55:10AM -0800, Martin KaFai Lau wrote:
> Provide a LRU version of the existing BPF_MAP_TYPE_PERCPU_HASH
> 
> Signed-off-by: Martin KaFai Lau <kafai@...com>
...
> +	/* For LRU, we need to alloc before taking bucket's
> +	 * spinlock because LRU's elem alloc may need
> +	 * to remove older elem from htab and this removal
> +	 * operation will need a bucket lock.
> +	 */
> +	if (map_flags != BPF_EXIST) {
> +		l_new = prealloc_lru_pop(htab, key, hash);
> +		if (!l_new)
> +			return -ENOMEM;
> +	}
> +
> +	/* bpf_map_update_elem() can be called in_irq() */
> +	raw_spin_lock_irqsave(&b->lock, flags);
> +
> +	l_old = lookup_elem_raw(head, hash, key, key_size);
> +
> +	ret = check_flags(htab, l_old, map_flags);
> +	if (ret)
> +		goto err;
> +
> +	if (l_old) {
> +		bpf_lru_node_set_ref(&l_old->lru_node);
> +
> +		/* per-cpu hash map can update value in-place */
> +		pcpu_copy_value(htab, htab_elem_get_ptr(l_old, key_size),
> +				value, onallcpus);
> +	} else {
> +		pcpu_copy_value(htab, htab_elem_get_ptr(l_new, key_size),
> +				value, onallcpus);
> +		hlist_add_head_rcu(&l_new->hash_node, head);
> +		l_new = NULL;
> +	}
> +	ret = 0;
> +err:
> +	raw_spin_unlock_irqrestore(&b->lock, flags);
> +	if (l_new)
> +		bpf_lru_push_free(&htab->lru, &l_new->lru_node);
> +	return ret;
> +}

definitely tricky code, but all looks correct.
Acked-by: Alexei Starovoitov <ast@...nel.org>