Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760127AbZGIKfk (ORCPT ); Thu, 9 Jul 2009 06:35:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756032AbZGIKfd (ORCPT ); Thu, 9 Jul 2009 06:35:33 -0400 Received: from fxip-0047f.externet.hu ([88.209.222.127]:46047 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752333AbZGIKfc (ORCPT ); Thu, 9 Jul 2009 06:35:32 -0400 To: tj@kernel.org CC: miklos@szeredi.hu, linux-kernel@vger.kernel.org, fuse-devel@lists.sourceforge.net, akpm@linux-foundation.org, npiggin@suse.de In-reply-to: <4A55286A.6040202@kernel.org> (message from Tejun Heo on Thu, 09 Jul 2009 08:14:50 +0900) Subject: Re: [PATCH 4/4] FUSE: implement direct mmap References: <1245317073-24000-1-git-send-email-tj@kernel.org> <1245317073-24000-5-git-send-email-tj@kernel.org> <4A48EEDC.807@kernel.org> <4A4F3998.5020805@kernel.org> <4A55286A.6040202@kernel.org> Message-Id: From: Miklos Szeredi Date: Thu, 09 Jul 2009 12:35:26 +0200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1382 Lines: 34 On Thu, 09 Jul 2009, Tejun Heo wrote: > >> Using non-swappable memory would be fine for most device emulations > >> but mapping large amount of pages would be problematic. Hmmm... this > >> is difficult. It's a compromise among flexibility, scalability and > >> code complexity. > > > > What's the difficulty? > > The desire to avoid pinning all the mapped pages. :-) > > > Allocating pages, giving them an ID and mapping them into various page > > tables seems simple in contrast to trying to make a tmpfs file be a > > fuse file at the same time, which the VM is really not prepared for. > > If pinning all the pages are okay, the above should work fine. If the page allocation is privileged then I think it's okay. I have only vague ideas how this "direct mmap" could be used for other things than sound drivers. For example there's a significant push towards making network filesystems coherent. This is currently not well supported by fuse and adding coherency guarantees to mmap is especially tricky. But I'm not sure it really needs a special mmap interface, that's just one of the options. Thoughts? Thanks, Miklos -- 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/