netdev - Re: [v2 PATCH 7/10] rhashtable: Disable automatic shrinking

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Message-ID: <20150323093632.GD16023@casper.infradead.org>
Date:	Mon, 23 Mar 2015 09:36:32 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Patrick McHardy <kaber@...sh.net>,
	Josh Triplett <josh@...htriplett.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	netdev@...r.kernel.org
Subject: Re: [v2 PATCH 7/10] rhashtable: Disable automatic shrinking

On 03/23/15 at 08:28pm, Herbert Xu wrote:
> On Mon, Mar 23, 2015 at 08:33:19AM +0000, Thomas Graf wrote:
> >
> > I'm not claiming you always want shrinking but what gain is there by
> > removing integrated support? Can you show numbers that the additional
> > branch actually hurts?
> 
> You never want automatic shrinking unless all your users are
> trusted.  I doubt there would be many rhashtable users where
> this would apply.  Even nft_hash is quite tenuous.

Why?

> Besdies, if you really want automatic shrinking, you could always
> do it in the caller of rhashtable_remove.  That way only you
> would pay for the cost and not everybody else.

Same can be said for growing. Why do we differ between the two?
Would you expect users requiring shrinking() to call
rhashtable_shrink() after every remove? Should they encode their
own logic based on rhashtable internals?
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