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

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Message-ID: <20161010140424.GB21057@breakpoint.cc>
Date:   Mon, 10 Oct 2016 16:04:24 +0200
From:   Florian Westphal <fw@...len.de>
To:     Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:     davem@...emloft.net, pablo@...filter.org, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, fw@...len.de
Subject: Re: [PATCH net 2/2] conntrack: enable to tune gc parameters

Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
> After commit b87a2f9199ea ("netfilter: conntrack: add gc worker to remove
> timed-out entries"), netlink conntrack deletion events may be sent with a
> huge delay. It could be interesting to let the user tweak gc parameters
> depending on its use case.

Hmm, care to elaborate?

I am not against doing this but I'd like to hear/read your use case.

The expectation is that in almot all cases eviction will happen from
packet path.  The gc worker is jusdt there for case where a busy system
goes idle.

> +nf_conntrack_gc_max_evicts - INTEGER
> +	The maximum number of entries to be evicted during a run of gc.
> +	This sysctl is only writeable in the initial net namespace.

Hmmm, do you have any advice on sizing this one?

I think a better change might be (instead of adding htis knob) to
resched the gc worker for immediate re-executaion in case the entire
"budget" was used.  What do you think?


diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -983,7 +983,7 @@ static void gc_worker(struct work_struct *work)
                return;
 
        ratio = scanned ? expired_count * 100 / scanned : 0;
-       if (ratio >= 90)
+       if (ratio >= 90 || expired_count == GC_MAX_EVICTS)
                next_run = 0;