Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758306AbXEaGOV (ORCPT ); Thu, 31 May 2007 02:14:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759394AbXEaGOM (ORCPT ); Thu, 31 May 2007 02:14:12 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:53749 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757235AbXEaGOK (ORCPT ); Thu, 31 May 2007 02:14:10 -0400 Date: Thu, 31 May 2007 08:13:03 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Davide Libenzi , Ulrich Drepper , Jeff Garzik , Zach Brown , Linux Kernel Mailing List , Arjan van de Ven , Christoph Hellwig , Andrew Morton , Alan Cox , Evgeniy Polyakov , "David S. Miller" , Suparna Bhattacharya , Jens Axboe , Thomas Gleixner Subject: Re: Syslets, Threadlets, generic AIO support, v6 Message-ID: <20070531061303.GA4436@elte.hu> References: <465CA654.5000505@garzik.org> <20070530072055.GA3077@elte.hu> <465D286E.2080807@redhat.com> <20070530084252.GA15708@elte.hu> <465DE992.6070803@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2077 Lines: 45 * Linus Torvalds wrote: > > I agree. What would be a good interface to allocate fds in such > > area? We don't want to replicate syscalls, so maybe a special new > > dup function? > > I'd do it with something like "newfd = dup2(fd, NONLINEAR_FD)" or > similar, and just have NONLINEAR_FD be some magic value (for example, > make it be 0x40000000 - the bit that says "private, nonlinear" in the > first place). > > But what's gotten lost in the current discussion is that we probably > don't actually _need_ such a private space. I'm just saying that if > the *choice* is between memory-mapped interfaces and a private > fd-space, we should probably go for the latter. "Everything is a file" > is the UNIX way, after all. But there's little reason to introduce > private fd's otherwise. it's both a flexibility and a speedup thing as well: flexibility: for libraries to be able to open files and keep them open comes up regularly. For example currently glibc is quite wasteful in a number of common networking related functions (Ulrich, please correct me if i'm wrong), which could be optimized if glibc could just keep a netlink channel fd open and could poll() it for changes and cache the results if there are no changes (or something like that). speedup: i suggested O_ANY 6 years ago as a speedup to Apache - non-linear fds are cheaper to allocate/map: http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg23820.html (i definitely remember having written code for that too, but i cannot find that in the archives. hm.) In theory we could avoid _all_ fd-bitmap overhead as well and use a per-process list/pool of struct file buffers plus a maximum-fd field as the 'non-linear fd allocator' (at the price of only deallocating them at process exit time). Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/