netdev - Re: [PATCH net 2/2] conntrack: enable to tune gc parameters

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Date:   Fri, 14 Oct 2016 12:53:27 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Florian Westphal <fw@...len.de>
Cc:     Nicolas Dichtel <nicolas.dichtel@...nd.com>, davem@...emloft.net,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH net 2/2] conntrack: enable to tune gc parameters

On Fri, Oct 14, 2016 at 12:37:26PM +0200, Florian Westphal wrote:
> Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
> > Le 13/10/2016 à 22:43, Florian Westphal a écrit :
[...]
> > > (Or cause too many useless scans)
> > > 
> > > Another idea worth trying might be to get rid of the max cap and
> > > instead break early in case too many jiffies expired.
> > > 
> > > I don't want to add sysctl knobs for this unless absolutely needed; its already
> > > possible to 'force' eviction cycle by running 'conntrack -L'.
> > > 
> > Sure, but this is not a "real" solution, just a workaround.
> > We need to find a way to deliver conntrack deletion events in a reasonable
> > delay, whatever the traffic on the machine is.
> 
> Agree, but that depends on what 'reasonable' means and what kind of
> uneeded cpu churn we're willing to add.
> 
> We can add a sysctl for this but we should use a low default to not do
> too much unneeded work.
> 
> So what about your original patch, but only add
> 
> nf_conntrack_gc_interval
> 
> (and also add instant-resched in case entire budget was consumed)?

I would prefer not to expose sysctl knobs, if we don't really know
what good default values are good, then we cannot expect our users to
know this for us.

I would go tune this in a way that this resembles to the previous
behaviour.