netdev - Re: [PATCH net v5] net/ipv6: Add anycast addresses to a global hashtable

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Date:   Tue, 30 Oct 2018 07:10:58 -0400
From:   Jeff Barnhill <0xeffeff@...il.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net v5] net/ipv6: Add anycast addresses to a global hashtable

I originally started implementing it the way you suggested; however,
it seemed to complicate management of that structure because it isn't
currently using rcu.  Also, assuming that can be worked out, where
would I get the net from?  Would I need to store a copy in ifcaddr6,
or is there some way to access it during ipv6_chk_acast_addr()?  It
seems that if I don't add a copy of net, but instead access it through
aca_rt(?), then freeing the ifcaddr6 memory becomes problematic
(detaching it from idev, while read_rcu may still be accessing it).
On Mon, Oct 29, 2018 at 11:32 PM David Miller <davem@...emloft.net> wrote:
>
> From: Jeff Barnhill <0xeffeff@...il.com>
> Date: Sun, 28 Oct 2018 01:51:59 +0000
>
> > +struct ipv6_ac_addrlist {
> > +     struct in6_addr         acal_addr;
> > +     possible_net_t          acal_pnet;
> > +     refcount_t              acal_users;
> > +     struct hlist_node       acal_lst; /* inet6_acaddr_lst */
> > +     struct rcu_head         rcu;
> > +};
>
> Please just add the hlist to ifcaddr6 instead of duplicating so much
> information and reference counters here.
>
> This seems to waste a lot of memory unnecessary and add lots of
> unnecessary object allocate/setup/destroy logic.