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Date: Thu, 12 Mar 2026 13:36:40 +0100
From: Florian Westphal <fw@strlen.de>
To: Prasanna S Panchamukhi <panchamukhi@arista.com>
Cc: netfilter-devel@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Simon Horman <horms@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Pablo Neira Ayuso <pablo@netfilter.org>, Phil Sutter <phil@nwl.cc>,
	netdev@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, coreteam@netfilter.org
Subject: Re: [PATCH net-next] netfilter: conntrack: expose
 gc_scan_interval_max via sysctl
Message-ID: <abKzWIhVz_SeiSOa@strlen.de>
References: <20260311194058.13860-1-panchamukhi@arista.com>
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In-Reply-To: <20260311194058.13860-1-panchamukhi@arista.com>

Prasanna S Panchamukhi <panchamukhi@arista.com> wrote:
> The conntrack garbage collection worker uses an adaptive algorithm that
> adjusts the scan interval based on the average timeout of tracked
> entries.  The upper bound of this interval is hardcoded as
> GC_SCAN_INTERVAL_MAX (60 seconds).
> 
> Expose the upper bound as a new sysctl,
> net.netfilter.nf_conntrack_gc_scan_interval_max, so it can be tuned at
> runtime without rebuilding the kernel.  The default remains 60 seconds
> to preserve existing behavior.  The sysctl is global and read-only in
> non-init network namespaces, consistent with nf_conntrack_max and
> nf_conntrack_buckets.

This was proposed before, see:

https://lore.kernel.org/netfilter-devel/aO-id5W6Tr7frdHN@strlen.de/
https://lore.kernel.org/netfilter-devel/aRsuU57juCvsMBKE@strlen.de/

I did not hear back wrt. the horizon cache.

I'm not 100% opposed to this, but I do wonder if we really can't do
better than the current avg strategy.