netdev - Re: [RFC PATCH bpf-next v2 0/4] Implement bpf queue/stack maps

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Date:   Thu, 6 Sep 2018 23:27:07 -0700
From:   Joe Stringer <joe@...d.net.nz>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     mauricio.vasquez@...ito.it, ast@...nel.org, daniel@...earbox.net,
        netdev <netdev@...r.kernel.org>, Joe Stringer <joe@...d.net.nz>
Subject: Re: [RFC PATCH bpf-next v2 0/4] Implement bpf queue/stack maps

On Thu, 6 Sep 2018 at 17:13, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> bpf_map_pop_elem() is trying to do lookup_and_delete and preserve
> validity of value without races.
> With pcpu_freelist I don't think there is a solution.
> We can have this queue/stack map without prealloc and use kmalloc/kfree
> back and forth. Performance will not be as great, but for your use case,
> I suspect, it will be good enough.
> The key issue with kmalloc/kfree is unbounded time of rcu callbacks.
> If somebody starts doing push/pop for every packet, the rcu subsystem
> will struggle and nothing we can do about it.
>
> The only way I could think of to resolve this problem is to reuse
> the logic that Joe is working on for socket lookups inside the program.
> Joe,
> how is that going? Could you repost the latest patches?

I can rebase & send them out. Was just wanting to get a little more testing in.

Cheers,
Joe