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netfilter: conntrack: adopt safer max chain length

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Customers using GKE 1.25 and 1.26 are facing conntrack issues
root caused to commit c9c3b6811f ("netfilter: conntrack: make
max chain length random").

Even if we assume Uniform Hashing, a bucket often reachs 8 chained
items while the load factor of the hash table is smaller than 0.5

With a limit of 16, we reach load factors of 3.
With a limit of 32, we reach load factors of 11.
With a limit of 40, we reach load factors of 15.
With a limit of 50, we reach load factors of 24.

This patch changes MIN_CHAINLEN to 50, to minimize risks.

Ideally, we could in the future add a cushion based on expected
load factor (2 * nf_conntrack_max / nf_conntrack_buckets),
because some setups might expect unusual values.

Fixes: c9c3b6811f ("netfilter: conntrack: make max chain length random")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Eric Dumazet 2023-03-07 05:22:54 +00:00 committed by Pablo Neira Ayuso
parent 4a02426787
commit c77737b736
1 changed files with 2 additions and 2 deletions
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4
net/netfilter/nf_conntrack_core.c
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@ -96,8 +96,8 @@ static DEFINE_MUTEX(nf_conntrack_mutex);
#define GC_SCAN_MAX_DURATION msecs_to_jiffies(10)
#define GC_SCAN_EXPIRED_MAX (64000u / HZ)
#define MIN_CHAINLEN 8u
#define MAX_CHAINLEN (32u - MIN_CHAINLEN)
#define MIN_CHAINLEN 50u
#define MAX_CHAINLEN (80u - MIN_CHAINLEN)
static struct conntrack_gc_work conntrack_gc_work;