From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: Supporting more devices with dev_alloc_name() Date: Thu, 25 Oct 2012 11:16:44 -0700 Message-ID: <20121025111644.301dc9d8@nehalam.linuxnetplumber.net> References: <20121025165632.GC7857@raven> <1351187443.6537.184.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Tom Parkin , netdev To: Eric Dumazet Return-path: Received: from mail.vyatta.com ([76.74.103.46]:50630 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758172Ab2JYSRc (ORCPT ); Thu, 25 Oct 2012 14:17:32 -0400 In-Reply-To: <1351187443.6537.184.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 25 Oct 2012 19:50:43 +0200 Eric Dumazet wrote: > On Thu, 2012-10-25 at 17:56 +0100, Tom Parkin wrote: > > Hi list, > > > > I've recently been trying to create large-scale L2TPv3 configurations > > of up to 50,000 Ethernet pseudowires. > > > > One of the limitations I've hit has been to do with dev_alloc_name(). > > By default, l2tp_eth uses "l2tpeth%d" for device names, which is > > expanded by dev_alloc_name() into l2tpeth1, l2tpeth2, etc. However, > > the algorithm dev_alloc_name() uses to derive the next free number for > > this scheme is bounded by the number of bits in a single page. For > > kernels/platforms with a 4kB page, this limits these "autoderived" > > names to 32k. > > > > In my testing I've been able to work around this by specifying > > interface names during the bringup of the l2tpeth interfaces, thereby > > bypassing dev_alloc_name() altogether. Using this approach I am able > > to comfortably create 50k interfaces, even on fairly modest hardware. > > But it seems a shame to have to do this; it would be much nicer if > > the kernel were able to autogenerate names for more devices. > > > > Is this something that would be worth my working on a patch for, or > > would the increased code complexity be too great an overhead to > > consider for such outlandish use-cases? > > This issue was raised some ago, for the dummy device > > modprobe dummy numdummies=33000 > > I guess each format (eg eth%d) could be attached/associated to an idr, > so that we can find the lowest available index very fast. You could try vzalloc() instead of get_zeroed_page which would allow for bigger bitmap.