netdev - Re: [PATCH v5] netfilter: nfnetlink_queue: optimize verdict lookup with hash table

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Message-ID: <CAFn2buDeCxJp3OHDifc5yX0pQndmLCKc=PShT+6Jq3-uy8C-OA@mail.gmail.com>
Date: Tue, 13 Jan 2026 20:32:56 -0500
From: Scott Mitchell <scott.k.mitch1@...il.com>
To: Pablo Neira Ayuso <pablo@...filter.org>
Cc: kadlec@...filter.org, fw@...len.de, phil@....cc, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, horms@...nel.org, 
	netfilter-devel@...r.kernel.org, coreteam@...filter.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot@...kaller.appspotmail.com
Subject: Re: [PATCH v5] netfilter: nfnetlink_queue: optimize verdict lookup
 with hash table

> > +     NFQA_CFG_HASH_SIZE,             /* __u32 hash table size (rounded to power of 2) */
>
> This should use the rhashtable implementation, I don't find a good
> reason why this is not used in first place for this enhancement.

Thank you for the review! I can make the changes. Before implementing,
I have a few questions to ensure I understand the preferred approach:

1. For the "perns" allocation comment - which approach did you have in mind:
  a) Shared rhashtable in nfnl_queue_net (initialized in
nfnl_queue_net_init) with key={queue_num, packet_id}
  b) Per-instance rhashtable in nfqnl_instance, with lock refactoring
so initialization happens outside rcu_read_lock
2. The lock refactoring (GFP_ATOMIC → GFP_KERNEL) is independent of
the hash structure choice, correct? We could fix that separately?
3. Can you help me understand the trade-offs you considered for
rhashtable vs hlist_head? Removing the API makes sense, and I want to
better understand how to weigh that against runtime overhead (RCU,
locks, atomic ops) for future design decisions.

I'll use a custom hashfn to preserve the current mask-based hashing
for the incrementing IDs.