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

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Message-ID: <20150116204921.GA14833@gondor.apana.org.au>
Date:	Sat, 17 Jan 2015 07:49:21 +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 Fri, Jan 16, 2015 at 07:35:57PM +0000, Patrick McHardy wrote:
> 
> Well, rhashtable (or generally resizing) will make it a lot worse.
> Usually we at worst miss entries which were added during the dump,
> which is made up by the notifications.
> 
> With resizing we might miss anything, its completely undeterministic.

Correct.  If you want to have a stable dump you will need to have
data structure outside the hash table.  For example, with xfrm_state
we do it with a linked list.

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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