netdev - Re: [RFC] net: ipv4 -- Introduce ifa limit per net

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Date:	Fri, 04 Mar 2016 16:08:30 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	gorcunov@...il.com, netdev@...r.kernel.org, solar@...nwall.com,
	vvs@...tuozzo.com, avagin@...tuozzo.com, xemul@...tuozzo.com,
	vdavydov@...tuozzo.com, khorenko@...tuozzo.com
Subject: Re: [RFC] net: ipv4 -- Introduce ifa limit per net

On ven., 2016-03-04 at 17:50 -0500, David Miller wrote:
> From: Cyrill Gorcunov <gorcunov@...il.com>
> Date: Sat, 5 Mar 2016 00:39:20 +0300
> 
> > Currenlty all the kernels (including vanilla) free ifa
> > list under rtln_lock() taken which takes a huge time
> > to release all entries when we stop the container.
> > Moreover it's allowed to create unlimited number
> > of addresses from inside of net-namespace if
> > CAP-NET_ADMIN granted (which is common for containers).
> > 
> > Lets introduce per-net limit (4096 by default)
> > of addresses, which can be tuned up via sysfs
> > entry /proc/sys/net/ipv4/ifa_limit.
> > 
> > Reported-by: Solar Designer <solar@...nwall.com>
> > Signed-off-by: Cyrill Gorcunov <gorcunov@...tuozzo.com>
> 
> Arbitrary limits are... arbitrary.
> 
> If the freeing loop is the issue, splice the list at teardown and
> process that list asynchronously via a workqueue or similar.
> 
> Thanks.

Also I wonder if the problem is not a quadratic behavior.

__inet_del_ifa() should probably take into account in_dev->dead  (no
promotion, no list scan...)