On Wed, 28 Feb 2018 20:28:15 -0800
Eric Dumazet <eric.duma...@gmail.com> wrote:
> On Wed, 2018-02-28 at 22:32 -0500, David Miller wrote:
> > From: Eric Dumazet <eric.duma...@gmail.com>
> > Date: Wed, 28 Feb 2018 18:28:02 -0800
> >
> > > How useful it is to report this information ?
> > >
> > > Given REUSEADDR and REUSEPORT, I really wonder what can be derived from
> > > this counter.
> > >
> > > It seems its semantic is weak.
> >
> > To me none of this really matters.
> >
> > What matters is that iproute2 reported this via slabinfo for longer
> > than a decade.
> >
> > It broke recently when SLAB started merging caches just like SLUB
> > always did.
>
>
> Linus himself removed some info that was much more useful in
> commit a5ad88ce8c7fae7d ("mm: get rid of 'vmalloc_info' from
> /proc/meminfo")
>
> # egrep "VmallocUsed|VmallocChunk" /proc/meminfo
> VmallocUsed: 0 kB
> VmallocChunk: 0 kB
>
> So I vote for not re-adding another loop in the kernel with no
> preemption point.
>
> Simply taking spinlocks like Stephen did is going to slow down the
> other threads, lets face it.
>
> This implementation has a high cost, and provides something that made
> no sense in the first place.
>
I went through a several possible alternatives.
1. Add a counter in the hash bucket head (like listen already has).
But not namespace aware
2. Add a percpu counter in network namespace (new struct tcp_netns)
Logical and adds place to move tcp open sockets as well.
But more expensive and several places in code don't have easy
access to namespace.
3. Counting entries in userspace; defeats the purpose of -s flag.
Agree it is not an urgent statistic, it is just it got broken; willing to
just drop it.
What about adding cond_resched between buckets like other places do?
