netdev - Re: [PATCH net-next 2/2] rhashtable: Quick initial growth of tables

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Date:	Fri, 1 May 2015 15:38:01 +0200
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, kaber@...sh.net
Subject: Re: [PATCH net-next 2/2] rhashtable: Quick initial growth of tables

On 05/01/15 at 12:37pm, Herbert Xu wrote:
> On Fri, May 01, 2015 at 06:30:25AM +0200, Thomas Graf wrote:
> >
> > Yes, that can happen. Since shrinks are ordered to the end of the
> > chain it is often the case that enough entries have been added so the
> > shrink is not carried out in the end. Obviously this is also not the
> > case if no entries are actually removed.
> 
> It's just a matter of logical consistency.  At 75% if you grow by
> a factor of 4, you get 18.75% utilisation which is way below the
> 30% shrink threshold.
> 
> > What about we apply quick growing on >100% utilization? It is a
> > clear indication that we are growing rapidly.
> 
> Even at 100%, a factor of 4 leads you to 25% which is less than 30%.
> 
> Perhaps we could lower the shrink thresholds? Alternatively, only
> grow quickly if automatic shrinking is disabled.  After all, the one
> case that's inspring all of this, netlink really wants to grow
> quickly as well as only shrink at specific points in time.

Lowering the shrink threshold in combination with quick growth
above 100% sounds good to me. The whole point of this is to detect
when we are likely to see a lot of inserts with only a few or no
removals.
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