netdev - Re: [PATCH] net: limit a number of namespaces which can be cleaned up concurrently

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Message-Id: <20161014.100913.2270132305131797982.davem@davemloft.net>
Date:   Fri, 14 Oct 2016 10:09:13 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     ebiederm@...ssion.com
Cc:     avagin@...tuozzo.com, avagin@...nvz.org, netdev@...r.kernel.org,
        containers@...ts.linux-foundation.org
Subject: Re: [PATCH] net: limit a number of namespaces which can be cleaned
 up concurrently

From: ebiederm@...ssion.com (Eric W. Biederman)
Date: Thu, 13 Oct 2016 22:06:28 -0500

> Oh that is a surprise.  We can definitely skip genenerating uevents for
> network namespaces that are exiting because by definition no one can see
> those network namespaces.  If a socket existed that could see those
> uevents it would hold a reference to the network namespace and as such
> the network namespace could not exit.
> 
> That sounds like it is worth investigating a little more deeply.
> 
> I am surprised that allocation and freeing is so heavy we are spending
> lots of time doing that.  On the other hand kobj_bcast_filter is very
> dumb and very late so I expect something can be moved earlier and make
> that code cheaper with the tiniest bit of work.

I definitely would rather see the uevents removed to kill ~%99 of the
namespace removal overhead rather than limiting.