netdev - Re: [PATCH] conntrack: Reduce conntrack count in nf_conntrack

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Date:	Tue, 24 Mar 2009 16:17:30 +0100
From:	Maxime Bizon <mbizon@...ebox.fr>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>,
	avorontsov@...mvista.com, Patrick McHardy <kaber@...sh.net>,
	netdev@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] conntrack: Reduce conntrack count in
	nf_conntrack_free()


On Tue, 2009-03-24 at 13:07 +0100, Eric Dumazet wrote:

Hi Eric,

> We use RCU to defer freeing of conntrack structures. In DOS situation,
> RCU might accumulate about 10.000 elements per CPU in its internal
> queues. To get accurate conntrack counts (at the expense of slightly
> more RAM used), we might consider conntrack counter not taking into
> account "about to be freed elements, waiting in RCU queues". We thus
> decrement it in nf_conntrack_free(), not in the RCU callback.

Your patch fixes the problem on my board too (embedded mips router
250Mhz), thanks.

Yet I'm concerned about what you said concerning RAM usage. I have a
very small amount on memory left on my board (less than 4M), and I tuned
ip route cache size and nf_conntrack_max to make sure I won't go OOM.

With your patch, does it mean 10000 conntrack entries can be allocated
while nf_conntrack_max is say only 2048 ?

Regards,

-- 
Maxime


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