netdev - Re: [PATCH 7/9] rhashtable: Per bucket locks & deferred expansion/shrinking

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Message-ID: <20150117101309.GA19585@gondor.apana.org.au>
Date:	Sat, 17 Jan 2015 21:13:10 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Thomas Graf <tgraf@...g.ch>,
	David Laight <David.Laight@...LAB.COM>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"john.r.fastabend@...el.com" <john.r.fastabend@...el.com>,
	"josh@...htriplett.org" <josh@...htriplett.org>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH 7/9] rhashtable: Per bucket locks & deferred
 expansion/shrinking

On Sat, Jan 17, 2015 at 09:51:46AM +0000, Patrick McHardy wrote:
> 
> I agree, however at least in the case of nftables you can easily do the same thing by adding millions of rules.

I think that's a problem in itself.  If a single packet can kill
the CPU through millions of rules, then namespaces would be a joke.
There has to be a limit to the number of rules or the processing
has to be deferred into thread context (thus subject to scheduler
control) at some point.

> It doesn't make things worse.

So I don't think that's a valid justification for ignoring this
hash table problem.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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