netdev - Re: debug: nt_conntrack and KVM crash

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Date:	Mon, 1 Feb 2010 12:25:24 +0200
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jon Masters <jonathan@...masters.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: debug: nt_conntrack and KVM crash

On Mon, Feb 1, 2010 at 12:12 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le lundi 01 février 2010 à 11:36 +0200, Alexey Dobriyan a écrit :
>> On Mon, Feb 1, 2010 at 11:32 AM, Jon Masters <jonathan@...masters.org> wrote:
>> > I hacked up a per-namespace version of hashtables (this needs doing
>> > anyway, since the global stuff is just waiting to break)
>>
>> Which ones? Conntrack hashtables are per-netns.
>
> It seems they are, but this is not a complete work :

They are per-netns.

It's not "complete", because right now there is no point in doing more.
nf_conntrack_max was rejected given the absense of per-netns kernel
memory consumption limiting.

> 1) Global settings (shared by all netns)

Only hashtable size which is module parameter and
there is no generic way to limit kernel memory (like beancounters).

> 2) nf_conntrack_cachep is shared, it should be not shared.

There is no need for it to be shared, unless you measured something.

> 3) nf_conntrack_untracked shared by all netns, it should be local.
>
> nf_conntrack_cleanup_net() can block forever because of this.
>
> while (atomic_read(&nf_conntrack_untracked.ct_general.use) > 1)
>        schedule();

This is known, yes, thinking on it, as naive way was agreed to suck.
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