[Devel] Re: [NETFILTER] early_drop() imrovement (v3)

[Patrick McHardy]

Vasily Averin wrote:
> +static int early_drop(const struct nf_conntrack_tuple *orig)
> +{
> +	unsigned int i, hash, cnt;
> +	int ret = 0;
> +
> +	hash = hash_conntrack(orig);
> +	cnt = NF_CT_PER_BUCKET;
> +
> +	for (i = 0;
> +		!ret && cnt && i < nf_conntrack_htable_size;
> +			++i, hash = ++hash % nf_conntrack_htable_size)
> +		ret = __early_drop(&nf_conntrack_hash[hash], &cnt);

Formatting is a bit ugly, looks much nicer as:

        for (i = 0; i < nf_conntrack_htable_size; i++) {

                ret = __early_drop(&nf_conntrack_hash[hash], &cnt);
                if (ret || !cnt)
                        break;
                hash = ++hash % nf_conntrack_htable_size;
        }

> @@ -1226,7 +1243,7 @@ int __init nf_conntrack_init(void)
>  		if (nf_conntrack_htable_size < 16)
>  			nf_conntrack_htable_size = 16;
>  	}
> -	nf_conntrack_max = 8 * nf_conntrack_htable_size;
> +	nf_conntrack_max = NF_CT_PER_BUCKET * nf_conntrack_htable_size;


I don't like the NF_CT_PER_BUCKET constant. First of all, each
conntrack is hashed twice, so its really only 1/2 of the average
conntracks per bucket. Secondly, its only a default and many
people use nf_conntrack_max = nf_conntrack_htable_size / 2, so
using this constant for early_drop seems wrong.

Perhaps make it 2 * nf_conntrack_max / nf_conntrack_htable_size
or even add a nf_conntrack_eviction_range sysctl.