netdev - Re: [v1 PATCH 1/14] rhashtable: Remove shift from bucket

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Message-ID: <20150317110041.GA11385@gondor.apana.org.au>
Date:	Tue, 17 Mar 2015 22:00:41 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"tgraf@...g.ch" <tgraf@...g.ch>
Cc:	David Laight <David.Laight@...LAB.COM>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [v1 PATCH 1/14] rhashtable: Remove shift from bucket_table

On Tue, Mar 17, 2015 at 10:56:57AM +0000, tgraf@...g.ch wrote:
>
> Given the discussions, the grow decision will likely change to
> a max bucket length limit anyway.

Actually no.  In my pathces the chain length is only used to
force an immediate rehash.  Growing is still based on the number
of elements.

The reason is that the maximum (not average) chain length actually
grows with the hash table size, even at 75% utilisation.

So unless we want ever decreasing utilisation as the table grows,
we have to cope with a few chains with many elements.  The limit
I'm currently using is 16 which shouldn't be hit even if you had
a 2^32 table (which you currently cannot).

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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