linux-kernel - Re: [PATCH 2.6.21-rc6] [netfilter] early

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Date:	Fri, 06 Apr 2007 17:08:28 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Vasily Averin <vvs@...ru>
CC:	Eric Dumazet <dada1@...mosbay.com>,
	"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 2.6.21-rc6] [netfilter] early_drop imrovement

Vasily Averin wrote:
> No, I've not investigated this scenario. It looks like you are right and my
> patch can leads to a long delays.
> 
> In my experiments I've decreased ip_conntrack_max lower than number of hash
> buckets and got the "table full, dropping packet" errors in logs. I've looked on
> the conntrack list and found a huge number of conntracks that can be freed.
> However my hash bucket was empty and therefore I even did not have any chances
> to free something. That's why I would like to check the other hash buckets too.
> 
> Ok, let's limit the number of conntracks that can be checked inside
> early_drop(). What do you prefer: some round number (for example 100) or
> fraction of ip_conntrack_max (for example 1%)?


A (small) fraction sounds better. We could even consider keeping track
of the number of conntracks that can be evicted (not assured), so in a
DOS situation we could save unnecessary table scans. Not sure if its
worth the effort though.

Anyway, please base your patch on the net-2.6.22 tree, which doesn't
include ip_conntrack anymore.

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