netdev - Re: [PATCH] inet: add bound ports statistic

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Date:   Wed, 28 Feb 2018 20:28:15 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     stephen@...workplumber.org, netdev@...r.kernel.org,
        sthemmin@...rosoft.com
Subject: Re: [PATCH] inet: add bound ports statistic

On Wed, 2018-02-28 at 22:32 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.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.