Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261738AbUCWAwQ (ORCPT ); Mon, 22 Mar 2004 19:52:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261760AbUCWAwQ (ORCPT ); Mon, 22 Mar 2004 19:52:16 -0500 Received: from waste.org ([209.173.204.2]:1933 "EHLO waste.org") by vger.kernel.org with ESMTP id S261738AbUCWAwK (ORCPT ); Mon, 22 Mar 2004 19:52:10 -0500 Date: Mon, 22 Mar 2004 18:52:04 -0600 From: Matt Mackall To: Matt Miller Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] 2.6: mmap complement, fdmap Message-ID: <20040323005204.GF8366@waste.org> References: <20040322190047.GC8366@waste.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.3.28i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1914 Lines: 44 On Mon, Mar 22, 2004 at 01:26:01PM -0600, Matt Miller wrote: > > > > a) what the hell for? > > > > > > It's targetted mainly as a performance enhancer. Some of the specific > > > scenarios where it would be useful are: > > > > > > a) When one cannot afford to take the performance hit of synchronizing > > > a memory range to disk due to disk size limitations or speed > > > requirements. > > > b) Some things can benefit from the ability to interface with > > memory as a > > > file. > > > > > > The specific reason for implementing this was to allow for > > loading dynamic > > > libraries in the context of a process without having to write them to > > > disk. > > > > How about tmpfs/ramfs instead? Open a file on tmpfs and mmap it and > > you've got the same thing without any of the nasty corner cases. > > Because tmpfs does not allow you to map a file descriptor to a specific > memory > range inside a process. tmpfs allows you to open a file that exists only > in memory, yes, but it does not accomplish what fdmap tries to accomplish. > fdmap allows you to access arbitrary memory ranges as if they were a file. > tmpfs allows you to access a file that happens to only exist in memory. > You do not control the address range that tmpfs/ramfs map to. You don't? Is this not what the first argument of mmap provides? I'm afraid I can't see how it matters, as you'd have to populate said map afterwards anyway. Point is, mmap() is already its own complement and what you're proposing is a hairy solution in search of a problem as the VFS maintainer already pointed out. -- Matt Mackall : http://www.selenic.com : Linux development and consulting - 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/