Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752973Ab2KTBYA (ORCPT ); Mon, 19 Nov 2012 20:24:00 -0500 Received: from moutng.kundenserver.de ([212.227.126.186]:55925 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751786Ab2KTBX6 (ORCPT ); Mon, 19 Nov 2012 20:23:58 -0500 Message-ID: <50AADBA8.4090507@vlnb.net> Date: Mon, 19 Nov 2012 20:23:52 -0500 From: Vladislav Bolkhovitin User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.2.28) Gecko/20120313 Mnenhy/0.8.5 Thunderbird/3.1.20 MIME-Version: 1.0 To: Chris Friesen CC: Ryan Johnson , General Discussion of SQLite Database , Nico Williams , linux-fsdevel@vger.kernel.org, "Theodore Ts'o" , linux-kernel , Richard Hipp Subject: Re: [sqlite] light weight write barriers References: <5086F5A7.9090406@vlnb.net> <20121025051445.GA9860@thunk.org> <508B3EED.2080003@vlnb.net> <20121027044456.GA2764@thunk.org> <5090532D.4050902@vlnb.net> <20121031095404.0ac18a4b@pyramind.ukuu.org.uk> <5092D90F.7020105@vlnb.net> <20121101212418.140e3a82@pyramind.ukuu.org.uk> <50931601.4060102@symas.com> <20121102123359.2479a7dc@pyramind.ukuu.org.uk> <50A1C15E.2080605@vlnb.net> <20121113174000.6457a68b@pyramind.ukuu.org.uk> <50A442AF.9020407@vlnb.net> <50A52133.9050204@cs.utoronto.ca> <50A56E43.3040805@genband.com> <50A71A7B.3040407@vlnb.net> In-Reply-To: <50A71A7B.3040407@vlnb.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V02:K0:VcMVmIowIEoxJbuobj0G4e2wcEua80B+RqBcCoT02qW RtgdUrIqjd6Phq9FG6TKG3+5Yenp6lQBGj4YIMI1DcUa3wvzwN LEyN7yHQ27or55VSymLtwpBlJiLz9RBZ98duPd5DMpYpaKV7Vn P5JtpLxqGzWdCSVS4V5JtaVJ1oLmOf8BHVE+XEGq5z15jCmTIN Yk+DpAjJbiwuf7xJknAHUbn1Gu/i8dJIW0k3xVHhddRIc34JIU d4qj06n+svm3+baPQCKIjKYdgSM69HXqfW3eSAgzrJzZg563Jx ZcjN+WGBI1sZpXmaa1lziA1k9BiuBM21kV8sj8svufOcQlTP44 +FXmhI1UF3RSbhJtSveU= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2311 Lines: 49 Vladislav Bolkhovitin, on 11/17/2012 12:02 AM wrote: >>> The easiest way to implement this fsync would involve three things: >>> 1. Schedule writes for all dirty pages in the fs cache that belong to >>> the affected file, wait for the device to report success, issue a cache >>> flush to the device (or request ordering commands, if available) to make >>> it tell the truth, and wait for the device to report success. AFAIK this >>> already happens, but without taking advantage of any request ordering >>> commands. >>> 2. The requesting thread returns as soon as the kernel has identified >>> all data that will be written back. This is new, but pretty similar to >>> what AIO already does. >>> 3. No write is allowed to enqueue any requests at the device that >>> involve the same file, until all outstanding fsync complete [3]. This is >>> new. >> >> This sounds interesting as a way to expose some useful semantics to userspace. >> >> I assume we'd need to come up with a new syscall or something since it doesn't >> match the behaviour of posix fsync(). > > This is how I would export cache sync and requests ordering abstractions to the > user space: > > For async IO (io_submit() and friends) I would extend struct iocb by flags, which > would allow to set the required capabilities, i.e. if this request is FUA, or full > cache sync, immediate [1] or not, ORDERED or not, or all at the same time, per > each iocb. > > For the regular read()/write() I would add to "flags" parameter of > sync_file_range() one more flag: if this sync is immediate or not. > > To enforce ordering rules I would add one more command to fcntl(). It would make > the latest submitted write in this fd ORDERED. Correction. To avoid possible races better that the new fcntl() command would specify that N subsequent read()/write()/sync() calls as ORDERED. For instance, in the simplest case of N=1, one next after fcntl() write() would be handled as ORDERED. (Unfortunately, it doesn't look like this old read()/write() interface has space for a more elegant solution) Vlad -- 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/