linux-kernel - Re: [PATCH nf-2.6.22] [netfilter] early

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Message-ID: <461789CF.8000106@cosmosbay.com>
Date:	Sat, 07 Apr 2007 14:08:47 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Vasily Averin <vvs@...ru>
CC:	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netfilter-devel@...ts.netfilter.org, rusty@...tcorp.com.au,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org
Subject: Re: [PATCH nf-2.6.22] [netfilter] early_drop imrovement

Vasily Averin a e'crit :
> When the number of conntracks is reached nf_conntrack_max limit, early_drop() is
> called and tries to free one of already used conntracks in one of the hash
> buckets. If it does not find any conntracks that may be freed, it
> leads to transmission errors.
> However it is not fair because of current hash bucket may be empty but the
> neighbour ones can have the number of conntracks that can be freed. On the other
> hand the number of checked conntracks is not limited and it can cause a long delay.
> The following patch limits the number of checked conntracks by average number of
> conntracks in one hash bucket and allows to search conntracks in other hash buckets.

Hi Vasily

> 
>  			atomic_inc(&ct->ct_general.use);
>  			break;
>  		}
> +		if (!--(*cnt)) {
> +			dropped = 1;
> +			break;
> +		}


> +	cnt = (nf_conntrack_max/nf_conntrack_htable_size) + 1;

I am sorry but this wont help in the case you mentioned in an earlier mail :

If nf_conntrack_max  < nf_conntrack_htable_size, cnt will be set to 1.

Then in __early_drop() you endup in breaking the list_for_each_entry_reverse() 
loop after the first element was tested ! Not what you intended I'm afraid, 
because you wont event scan the whole chain as before your patch :(

I believe you should not test --cnt in __early_drop() but in the caller.

(That is not counting the number of found cells, but the number of hash chains 
you tried)


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