netdev - Re: [v3 PATCH 9/9] rhashtable: Add immediate rehash during insertion

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Date:	Mon, 23 Mar 2015 21:56:32 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Patrick McHardy <kaber@...sh.net>,
	Josh Triplett <josh@...htriplett.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	netdev@...r.kernel.org
Subject: Re: [v3 PATCH 9/9] rhashtable: Add immediate rehash during insertion

On 03/24/15 at 08:44am, Herbert Xu wrote:
> I specifically made it this way because I don't think the users
> should be touching the actual limit.  This is something that you
> always want to enable unless you're in the situation of netfilter
> where you don't care.
> 
> If you did care then 16 is sort of intrinsic to the 32-bit hash
> that we're using.  Going below doesn't make much sense because
> you may run into false warnings due to double rehashes (that's
> how I discovered 4 was uesless, very quickly :) Remember the
> rehash is only there to detect pathological cases where people
> are actively attacking us.  Otherwise the 100% utilisation check
> will kick in.
> 
> Going above 16 means that you're hashing multiple objects with
> the same key.  Then you'd want to disable this altogether.
> 
> The rhashtable already has too many knobs and I don't want to
> add anything unnecessary to rhashtable_params.

OK. I can certinaly live with this. You are certinaly right that
simplicity isn't a bad move here. Thanks for being patience and
answering all the questions.

Acked-by: Thomas Graf <tgraf@...g.ch>
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