netdev - Re: [PATCH net-next] rhashtable: remove insecure_max

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Message-ID: <20170425141749.GD11322@breakpoint.cc>
Date:   Tue, 25 Apr 2017 16:17:49 +0200
From:   Florian Westphal <fw@...len.de>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] rhashtable: remove insecure_max_entries param

Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Tue, Apr 25, 2017 at 01:23:56PM +0200, Florian Westphal wrote:
> >
> > What extra cost?
> > 
> > The only change is that ht->nelems has to be right-shifted by one,
> > I don't think that warrants extra space in struct rhashtable, its
> > already way too large (I think we can reduce its size further).
> 
> I see at least one hole on 64-bit which means that you can fit
> it into struct rhashtable for free.

I'd rather close that hole by removing more stuff from rhastable and
rhashtable_params structs instead.

F.e. why do we need to have two key_len (one in params, one in
struct rhashtable)?

Or why does rhashtable use size_t in rhashtable_params to e.g. store
a key offset? Just using 'unsigned int' instead would shrink
rhashtable_params by 16 bytes.

I'd have less of an issue with this if we'd be talking about
something computationally expensive, but this is about storing
an extra value inside a struct just to avoid one "shr" in insert path...