Subject: Re: [PATCH 06/26] netfilter: conntrack: align nf_conn on cacheline boundary

From: Florian Westphal <[email-masked]>
Date: Wed, 6 Jul 2016 17:01:25 +0200

David Laight <[email-masked]> wrote:
> From: Pablo Neira Ayuso
> > Sent: 06 July 2016 15:24
> > From: Florian Westphal <[email-masked]>
> > 
> > increases struct size by 32 bytes (288 -> 320), but it is the right thing,
> > else any attempt to (re-)arrange nf_conn members by cacheline won't work.
> ...
> >  	nf_conntrack_cachep = kmem_cache_create("nf_conntrack",
> >  						sizeof(struct nf_conn), 0,
> > -						SLAB_DESTROY_BY_RCU, NULL);
> > +						SLAB_DESTROY_BY_RCU | SLAB_HWCACHE_ALIGN, NULL);
> 
> What happens on systems with cache lines that are longer than 64 bytes?

Sorry, I don't have a secret decoder ring.

HWCACHE_ALIGN is used for several other net slab caches, including
skbuff, so why is this a problem here?