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

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Message-ID: <20150517013829.GB5161@gondor.apana.org.au>
Date:	Sun, 17 May 2015 09:38:29 +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 Sat, May 16, 2015 at 06:09:46PM -0400, David Miller wrote:
>
> Obviously something like 50 or 100 is too much.
> 
> Perhaps something between 5 and 10.

You are even more parsimonious than I :) Because the maximum chain
length grows at a rate of logN * loglogN, I had chosen the number
16 which should be sufficient even if you had a 2^32 table (which
you currently can't as we max out somewhere below that).

FWIW Thomas did some numbers on this and apparent 10 gets breached
in a 2^24 table at 100% utilisation.

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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