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

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Message-ID: <20150116160354.GI30132@acer.localdomain>
Date:	Fri, 16 Jan 2015 16:03:55 +0000
From:	Patrick McHardy <kaber@...sh.net>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	kernel@...r.kernel.org, herbert@...dor.apana.org.au,
	paulmck@...ux.vnet.ibm.com, edumazet@...gle.com,
	john.r.fastabend@...el.com, josh@...htriplett.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 03:34pm, Patrick McHardy wrote:
> > On 15.12, Thomas Graf wrote:
> > > In the event of an expansion or shrinking, the new bucket table allocated
> > > is exposed as a so called future table as soon as the resize process
> > > starts.  Lookups, deletions, and insertions will briefly use both tables.
> > > The future table becomes the main table after an RCU grace period and
> > > initial linking of the old to the new table was performed. Optimization
> > > of the chains to make use of the new number of buckets follows only the
> > > new table is in use.
> > 
> > AFAICT nft_hash_walk() will miss new entries during this period.
> > Am I missing anything here?
> 
> A walker may not see insertions that occur after the walker was started
> if resizing is enabled. Is that a problem for nftables?

No, that would be Ok. The case I'm wondering about is:

- insertion
- resize starts
- another insertion
- walker, resize not finished yet
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