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

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Message-ID: <20150116191831.GA26730@casper.infradead.org>
Date:	Fri, 16 Jan 2015 19:18:31 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Patrick McHardy <kaber@...sh.net>
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 01/16/15 at 06:36pm, Patrick McHardy wrote:
> 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.

Right,but that's a Netlink dump issue and not specific to rhashtable.
Putting the sequence number check in place should be sufficient
for sets, right?
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