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

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Message-ID: <20150116183626.GS30132@acer.localdomain>
Date:	Fri, 16 Jan 2015 18:36:26 +0000
From:	Patrick McHardy <kaber@...sh.net>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	David Laight <David.Laight@...LAB.COM>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"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 16.01, Thomas Graf wrote:
> On 01/16/15 at 04:43pm, David Laight wrote:
> > The walker is unlikely to see items that get inserted early in the hash
> > table even without a resize.
> 
> I don't follow, you have to explain this statement.
> 
> Walkers which don't want to see duplicates or miss entries should
> just take the mutex.

Well, we do have a problem with interrupted dumps. As you know once
the netlink message buffer is full, we return to userspace and
continue dumping during the next read. Expanding obviously changes
the order since we rehash from bucket N to N and 2N, so this will
indeed cause duplicate (doesn't matter) and missed entries.
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