netdev - Re: [PATCH net-next 1/3] rhashtable: Add a function for in order insertion in buckets

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Message-ID: <20150715010806.GA30213@gondor.apana.org.au>
Date:	Wed, 15 Jul 2015 09:08:06 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Tom Herbert <tom@...bertland.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Thomas Graf <tgraf@...g.ch>, Kernel Team <kernel-team@...com>
Subject: Re: [PATCH net-next 1/3] rhashtable: Add a function for in order
 insertion in buckets

On Tue, Jul 14, 2015 at 05:59:53PM -0700, Tom Herbert wrote:
>
> Conceptually, I agree with you, but I would point out that we've had
> this model of intentional collisions for a while in socket lookup. I
> would assume that it's a goal to use rhashtable for socket tables, so
> we'll need some solution that works with that!

Why you couldn't have them hang off a node as I described earlier?

> > The other reason I wanted to have this logic outside of rhashtable
> > is because for IPsec, the wildcards may in fact change after a
> > "rehash".  For example we may move from a /32 granularity to a
> > /31 granlarity at the requst of the admin.  In that case you can't
> > just mix the chain from the old table with the new.
> >
> Where ordering elements in the table can't be sustained, scoring would
> be used (e.g. scoring function can be changed on the fly, but ordering
> rules can't be).

I'm not sure whether we're talking about the same thing here.

Let me describe the IPsec case more clearly.  We have wildcards
and non-wildcards.  Only the non-wildcards would be hashed.  The
wild cards are checked outside of the hash table.  The tricky bit
is that the admin can flip a switch and we may either have to move
previously wildcard entries that are no longer wildcards into the
hash table, or move non-wildcard entries out of the table and into
the wildcard list.

And of course we want to do this without imposing locking on the
reader :)

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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