linux-kernel - Re: [PATCH V3] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack

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Message-Id: <20250410130531.17824-1-xiafei_xupt@163.com>
Date: Thu, 10 Apr 2025 21:05:31 +0800
From: lvxiafei <xiafei_xupt@....com>
To: fw@...len.de
Cc: coreteam@...filter.org,
	davem@...emloft.net,
	edumazet@...gle.com,
	horms@...nel.org,
	kadlec@...filter.org,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	lvxiafei@...setime.com,
	netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org,
	pabeni@...hat.com,
	pablo@...filter.org,
	xiafei_xupt@....com
Subject: Re: [PATCH V3] netfilter: netns nf_conntrack: per-netns net.netfilter.nf_conntrack_max sysctl

Florian Westphal <fw@...len.de> wrote:
> I suggest to remove nf_conntrack_max as a global variable,
> make net.nf_conntrack_max use init_net.nf_conntrack_max too internally,
> so in the init_net both sysctls remain the same.

The nf_conntrack_max global variable is a system calculated
value and should not be removed.
nf_conntrack_max = max_factor * nf_conntrack_htable_size;

> When a new conntrack is allocated, then:
>
> If the limit in the init_net is lower than the netns, then
> that limit applies, so it provides upper cap.
>
> If the limit in the init_net is higher, the lower pernet limit
> is applied.
>
> If the init_net has 0 setting, no limit is applied.

If the init_net has 0 setting, it should depend on the
limit of other netns.

The netns Limit Behavior:
+------------------------+--------------------+-----------------------+
| init_net.ct.sysctl_max | net->ct.sysctl_max | netns Limit Behavior  |
+------------------------+--------------------+-----------------------+
| 0                      | 0                  | No limit              |
+------------------------+--------------------+-----------------------+
| 0                      | Non-zero           | net->ct.sysctl_max    |
+------------------------+--------------------+-----------------------+
| Non-zero               | 0                  | init_net.ct.sysctl_max|
+------------------------+--------------------+-----------------------+
| Non-zero               | Non-zero           | min                   |
+------------------------+--------------------+-----------------------+

net_ct_sysctl_max = likely(a && b) ? min(a, b) : max(a, b);
or
net_ct_sysctl_max = unlikely(a == 0 || b == 0) ? max(a, b) : min(a, b);

if (net_ct_sysctl_max && unlikely(ct_count > net_ct_sysctl_max)) { ...