netdev - Re: rhashtable: Add cap on number of elements in hash table

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Message-ID: <20150518223526.GA25597@gondor.apana.org.au>
Date:	Tue, 19 May 2015 06:35:26 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	johannes@...solutions.net, netdev@...r.kernel.org, kaber@...sh.net,
	tgraf@...g.ch, johannes.berg@...el.com
Subject: Re: rhashtable: Add cap on number of elements in hash table

On Mon, May 18, 2015 at 04:12:01PM -0400, David Miller wrote:
>
> Ok, this of course depends upon the distribution of the input data
> and the strength/suitability of the hash function.
> 
> I'm a little bit disappointed in what Thomas found.  I would expect
> the distribution to be at least a little bit better.

Just to make it clear this is not a problem with uneven distribution.
The same thing would happen with any hash function.  It's essentially
a generalised birthday paradox.

Of course the average chain length is still what you expect it to
be, it's only the maximum chain length that grows at logN loglogN.

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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