From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754182AbZHJWwO (ORCPT ); Mon, 10 Aug 2009 18:52:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754124AbZHJWwM (ORCPT ); Mon, 10 Aug 2009 18:52:12 -0400 Received: from mx2.redhat.com ([66.187.237.31]:46640 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753847AbZHJWwL (ORCPT ); Mon, 10 Aug 2009 18:52:11 -0400 Message-ID: <4A80A37C.9000808@redhat.com> Date: Mon, 10 Aug 2009 12:47:24 -1000 From: Zachary Amsden User-Agent: Thunderbird 2.0.0.19 (X11/20090317) MIME-Version: 1.0 To: Pavel Machek CC: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, axboe@kernel.dk, hch@infradead.org, akpm@linux-foundation.org, Paul.Clements@steeleye.com, tytso@mit.edu Subject: Re: [PATCH] Allow userspace block device implementation References: <4A6D79F6.3050509@redhat.com> <20090807180841.GC1728@ucw.cz> In-Reply-To: <20090807180841.GC1728@ucw.cz> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Pavel Machek wrote: > Hi! Hey! > And yes, I believe that's show stopper. OTOH if you _can_ solve > that... then you have some rather significant advantage over nbd. > > (But guaranteeing progress for dirty writeout will be tricky even with > mlocked userland, AFAICT...) Actually, impossible, even with mlocked userland (*) which is what led me to abandon going any further with it. The problem is, to commit any data, one must make a system call, thus consuming more resources. It's merely a toy, nothing more. Sometimes it might be a useful toy, as nbd, but nbd, being in kernel, has at least a better chance of solving the swap problem. (*) strictly speaking, it is possible to guarantee progress of the device for read/write only to a finite region of mlocked memory and an infinite region (limited only by size of off_t) of read-only data computable with finite mlocked space. Obviously, neither of these (swap-to-ram), and (swap-over-ro-media) are actually useful for swap. Zach